J A G U A R S E R V I C E T R A I N I N G

JAGUAR ENGINE MANAGEMENT SYSTEMS:

AJ16 OBD II; AJ6 OBD I; V12 OBD I/II

SELF STUDY

SELF-STUDY TRAINING COURSE 801S

This publication is intended for instructional purposes only. Always refer to the appropriate
Jaguar Service publication for specific details and procedures.

All rights reserved. All material contained herein is based on the latest information available at the time of
publication. The right is reserved to make changes at any time without notice.

Publication T801S
© 2000 Jaguar Cars
PRINTED IN USA
 Service Training

INTRODUCTION
Welcome to the Jaguar Engine Management Systems Self-Study Course. This course is intended to
provide an overview of Jaguar Engine Management Systems prior to your attending the instructor-
led Jaguar Service Training Course: V6/V8 Engine Management. The contents of this self-study
book also serve as your archival information for earlier Jaguar engine management systems.

This course and the accompanying test must be completed prior to attending the Jaguar Service
Training Course: V6/V8 Engine Management unless you have already completed the instructor-led
Service Training Course 801.

To complete this course:

• Thoroughly review the material in this manual, which is categorized by system version.
• Once you have invested adequate study time, review the Student Proficiency Test at the end of
this manual.
• Fill out the answer sheet, making sure you include your name, your Social Security number
and your Dealer Name.
• When complete, fax or mail your answer sheet to:
Jaguar Cars Service Training Department
ATTN: Service Training Administrator
555 MacArthur Boulevard
Mahwah, New Jersey 07430
FAX: (201) 818-9074

Thank you for your participation.

J A G U A R S E R V I C E T R A I N I N G

JAGUAR ENGINE MANAGEMENT SYSTEMS:

CONTROL FUNDAMENTALS

1 ENGINE MANAGEMENT SYSTEMS

CONTROL OVERVIEW

2 JAGUAR ENGINE MANAGEMENT

SYSTEMS

CONTROL
FUNDAMENTALS

Service Training Course 801S

JAGUAR EMS: CONTROL FUNDAMENTALS
Service Training

ENGINE MANAGEMENT SYSTEM (EMS) CONTROL OVERVIEW

The primary purpose of engine management is to provide comprehensive engine control, which will produce a low lev-
el of vehicle powertrain emissions that meets clean air quality standards.

Powertrain emission sources:

• Engine exhaust emission
• Evaporative emissions from the fuel system and engine crankcase

In addition to emission control, the EMS must deliver:

• High quality engine operation
• Powertrain performance
• Vehicle drive quality

Clean air quality standards are interpreted into motor vehicle emission legislation that is known as On Board Diagnos-
tics (OBD).
The first level OBD applied through vehicle model year 1994 and is known as OBD I.
The second level OBD applied to vehicle model year 1995 and remains in effect today. This standard is known
as OBD II.
OBD standards are constantly evolving to produce a continuing reduction in vehicle powertrain emissions. As these
standards evolve, engine management systems must become more comprehensive and more capable in order to meet
the ever more stringent standards.

NOTES

1.2 Student Guide

JAGUAR EMS: CONTROL FUNDAMENTALS
Service Training

Engine Control Module (ECM)

The engine management system is centered around a digital engine control module (ECM). The ECM receives input sig-
nals from engine sensors to evaluate engine operating conditions. In addition, the ECM communicates with other
powertrain systems and vehicle systems. The ECM then processes the sensor information and the information received
from other systems using programmed software strategies and issues control output signals to the engine and emission
control functional systems.

At its very basic level of control the ECM:

• takes engine speed and load input signals
• applies correction factor inputs and emissions control feedback signals
• processes the signals to access pre-programmed software strategies
• outputs control signals to the various engine and emission components.

During this process, the ECM employs diagnostic tests to monitor and report engine management system faults. Faults are
stored in ECM memory as codes. Technician access to the fault codes and data is gained through a diagnostic data link.

BASIC ENGINE MANAGEMENT CONTROL

INPUTS PROCESSING OUTPUTS

ECM
ENGINE SPEED

ENGINE LOAD FUEL INJECTION CONTROL

INPUT SIGNAL PROCESSING
ENGINE CORRECTION FACTORS IGNITION CONTROL
CONTROL OUTPUTS
EMISSIONS CONTROL FEEDBACK EMISSION CONTROL
DIAGNOSTIC MONITORING

POWERTRAIN DIAGNOSTIC DATA LINK

VEHICLE

TPTEC.115

NOTES

Student Guide 1.3

JAGUAR EMS: CONTROL FUNDAMENTALS
Service Training

1.4 Student Guide

J A G U A R S E R V I C E T R A I N I N G

JAGUAR ENGINE MANAGEMENT SYSTEMS:

CONTROL FUNDAMENTALS

1 ENGINE MANAGEMENT SYSTEMS

CONTROL OVERVIEW

2 JAGUAR ENGINE MANAGEMENT

SYSTEMS

CONTROL
FUNDAMENTALS

Important note regarding the information contained in this section:

The systems and components described herein are intended only to give the reader a
foundation on which to build a complete understanding of current Jaguar engine manage-
ment systems. Therefore, the information is based on out of production systems, which
have less comprehensive control functions.

Certain sub systems, components, and functions may not apply directly to a specific
engine management system, or may be added or deleted for the sake of clarity.

For a complete understanding of a specific Jaguar engine management system, refer to the
publication(s) describing that system.

Service Training Course 801S

JAGUAR EMS: CONTROL FUNDAMENTALS
Service Training

JAGUAR ENGINE MANAGEMENT SYSTEMS

Jaguar engine management systems achieve reduced powertrain emissions by combining ECM control with other
mechanical and vacuum operated systems. These systems can generally be recognized by a mechanical throttle sys-
tem. The combined systems include the following:

• Fuel injection control – grouped fuel injection

• Ignition control – timing
• Idle intake air control
• Control of emission related systems and components such as:
– Evaporative emissions canister purge valve
– Exhaust gas recirculation
– Air injection
• Interface (hard wire) with other powertrain components such as:
– Engine cranking
– Transmission control module (TCM)
– A/C compressor clutch
– Instrument pack
• Interface (hard wire) with other vehicle systems such as:
– Instrument pack
• Engine related mechanical and vacuum operated systems considered part of engine management:
– Throttle body and air intake system
– Ignition distributor
– Exhaust system / catalytic converter(s)
– Fuel tank, piping and evaporative emission equipment
– Fuel pressure regulator and fuel rail
• Adaptive learning:
– Idle fuel metering
• On-board diagnostic monitoring and reporting:
– Diagnostic monitoring
– Engine default operation
– Diagnostic data link

NOTES

2.2 Student Guide

JAGUAR EMS: CONTROL FUNDAMENTALS
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JAGUAR ENGINE MANAGEMENT SYSTEM

INPUTS PROCESSING OUTPUTS

ENGINE SENSORS ECM ENGINE CONTROL

ENGINE SPEED FUEL PUMP
CRANKSHAFT POSITION GROUPED FUEL INJECTION
ENGINE LOAD IGNITION TIMING
ENGINE TEMPERATURE IDLE SPEED
INTAKE AIR TEMPERATURE EVAPORATIVE EMISSION
PURGE VALVE
DRIVER DEMAND
EXHAUST GAS RECIRCULATION
EXHAUST OXYGEN CONTENT
AIR INJECTION
EGR FEEDBACK
ENGINE SPEED LIMIT
ENGINE DEFAULT OPERATION

INPUT SIGNAL PROCESSING

CONTROL OUTPUTS
POWERTRAIN POWERTRAIN
ADAPTIVE LEARNING
TRANSMISSION TRANSMISSION
CONTROL MODULE DIAGNOSTIC MONITORING CONTROL MODULE
• PARK / NEUTRAL • ENGINE SPEED
• SHIFT IN PROGRESS • ENGINE LOAD
A/C COMPRESSOR CLUTCH • DRIVER DEMAND

ENGINE CRANKING

VEHICLE VEHICLE
INSTRUMENT PACK INSTRUMENT PACK
• VEHICLE SPEED • ENGINE SPEED
• FUEL QUANTITY • FUEL USED
INERTIA SWITCH • OBD FAULT WARNING
DIAGNOSTIC DATA LINK

TPTEC.116

Student Guide 2.3

JAGUAR EMS: CONTROL FUNDAMENTALS
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JAGUAR ENGINE MANAGEMENT SYSTEMS

Engine Control Module Inputs ECM INPUTS

Engine speed / crankshaft position

The crankshaft position sensor (CKP Sensor) is an inductive pulse generator that supplies the
ECM with both an engine speed and crankshaft position alternating voltage signal. The sensor is
located either on the timing cover or at the rear of the engine.
The reluctor, mounted on the crankshaft, has a number of “teeth” with one or two removed to
form a gap, which creates a missing pulse. The missing pulse allows the ECM to determine the
crankshaft position for fuel injector pulse synchronization.
Engine speed is one of the two main factors in determining fuel injector pulse duration (fuel
metering) and ignition timing.

Engine load
Engine load is the other main factor in determining fuel injector pulse duration (fuel metering)
and ignition timing.
Single throttle engines use a mass air flow sensor (MAF Sensor), located in the air intake before
the throttle body to measure the volume of air entering the engine. The MAF sensor is a “hot
wire” type sensor, which produces a voltage input signal to the ECM. The voltage input signal
allows the ECM to determine intake air volume, which it interprets as engine load.
Two throttle engines (V12) use one or two manifold absolute pressure sensors (MAP Sensor),
which sense engine intake manifold absolute pressure. The sensors connect to the intake mani-
folds downstream from the throttle valves so that manifold absolute pressure changes (opening /
closing throttle valve) act on the MAP sensor element. The MAP sensors produce a voltage input
signal to the ECM. The voltage input signal allows the ECM to determine engine load.
ECM
Engine temperature
Engine temperature is determined from the coolant temperature. The engine coolant tempera-
ture sensor (ECT Sensor) is a negative temperature coefficient (NTC) thermistor, located in the
engine coolant system. Its resistance decreases with an increase in coolant temperature. The
varying resistance creates a voltage drop that is sensed by the ECM.

Driver demand
Driver demand is determined from throttle valve position and the rate of change in throttle valve
position (open / close). The throttle position sensor (TP Sensor) is a rotary potentiometer con-
nected to the throttle valve shaft that supplies the ECM with a throttle position voltage signal.

Exhaust oxygen content

The exhaust system utilizes a three-way catalytic converter to significantly reduce exhaust emis-
sion. Catalytic converters require optimum combustion to operate efficiently. Optimum
combustion is defined as “stoichiometric”, a air : fuel ratio that is neither “lean” or “rich” for the
prevailing engine operating condition. In order to maintain the air : fuel ratio as close to stoichi-
ometric as possible, an exhaust gas oxygen content sensor (O2 Sensor) is used to provide the
ECM with a feedback signal in the form of an air : fuel ratio lean / rich “voltage swing”. The ECM
uses the feedback signal to shift the injector pulse duration toward rich or lean as required to
achieve stoichiometric. Two different types of sensors are used to produce a voltage swing: zir-
conium dioxide sensors and titanium dioxide sensors.

2.4 Student Guide

JAGUAR EMS: CONTROL FUNDAMENTALS
Service Training

ECM INPUTS

Intake air temperature

The intake air temperature sensor (IAT Sensor) is a a negative temperature coefficient (NTC) ther-
mistor located in the engine air intake system. Its resistance decreases with an increase in intake
air temperature. The varying resistance creates a voltage drop that is sensed by the ECM.

Exhaust gas recirculation feedback

A feedback signal from the EGR system enables the ECM to monitor the flow of exhaust gas into
the engine intake manifold.

Transmission
The ECM receives a transmission Park / Neutral signal (ground / open). The transmission control
module signals the ECM before shifting so that the ECM can momentarily reduce engine torque.

A/C compressor clutch

The ECM receives a compressor clutch engaged signal (B+ / ground) that is used for idle speed
compensation.

Engine cranking
When the engine is cranked (starter engaged), the ECM receives a cranking signal from the starter ECM
relay.

Instrument pack
The instrument pack provides the ECM with vehicle speed and fuel quantity signals.

Inertia switch
If the vehicle is impacted from the front or rear, an inertia switch switches off all ignition switched
power supply, thus de-energizing the fuel pump relay and de-activating the fuel pump.

Student Guide 2.5

JAGUAR EMS: CONTROL FUNDAMENTALS
Service Training

JAGUAR ENGINE MANAGEMENT SYSTEMS

Engine Control Module Input Processing
JAGUAR ENGINE MANAGEMENT SYSTEM

INPUTS PROCESSING OUTPUTS

ENGINE SENSORS ECM ENGINE CONTROL

ENGINE SPEED FUEL PUMP
CRANKSHAFT POSITION GROUPED FUEL INJECTION
ENGINE LOAD IGNITION TIMING
ENGINE TEMPERATURE IDLE SPEED
INTAKE AIR TEMPERATURE EVAPORATIVE EMISSION
PURGE VALVE
DRIVER DEMAND
EXHAUST GAS RECIRCULATION
EXHAUST OXYGEN CONTENT
AIR INJECTION
EGR FEEDBACK
ENGINE SPEED LIMIT
ENGINE DEFAULT OPERATION

INPUT SIGNAL PROCESSING

CONTROL OUTPUTS
POWERTRAIN POWERTRAIN
ADAPTIVE LEARNING
TRANSMISSION TRANSMISSION
CONTROL MODULE DIAGNOSTIC MONITORING CONTROL MODULE
• PARK / NEUTRAL • ENGINE SPEED
• SHIFT IN PROGRESS • ENGINE LOAD
A/C COMPRESSOR CLUTCH • DRIVER DEMAND

ENGINE CRANKING

VEHICLE VEHICLE
INSTRUMENT PACK INSTRUMENT PACK
• VEHICLE SPEED • ENGINE SPEED
• FUEL QUANTITY • FUEL USED
INERTIA SWITCH • OBD FAULT WARNING
DIAGNOSTIC DATA LINK

TPTEC.116

2.6 Student Guide

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ECM PROCESSING
Using programmed strategies, the ECM processes the input signals to determine the engine management control out-
puts necessary to achieve the specified emission level and engine performance during all phases of engine operation
including:
• Start and warm-up
• Normal operation
• Idle
• Acceleration / deceleration
• Diagnostic monitoring / default operation

The inputs are used for the following purposes:

• Engine speed and load Fuel injector pulse duration; ignition timing; engine speed limiting.
• Crankshaft position Fuel injector pulse timing.
• Engine coolant temperature Fuel injector pulse duration; ignition timing correction; idle speed stabilization;
air injection activation.
• Intake air temperature Ignition timing correction.
• Driver demand Fuel injector pulse duration; ignition timing correction; fuel cut-off (throttle over-run, wide
open throttle before engine start).
• Exhaust oxygen content “Closed loop” fuel metering (injector pulse duration) control.
• Exhaust gas recirculation feedback EGR diagnostic monitoring.
• Transmission Park / Neutral Idle speed stabilization.
• Transmission shift Engine torque reduction (momentarily retarding ignition timing).
• A/C compressor clutch Idle speed stabilization.
• Engine cranking Start-up injector pulse duration; start-up ignition timing; start-up idle air flow.
• Vehicle speed Idle speed control functions.
• Fuel quantity Fuel metering diagnostics canceled when the fuel level falls below a specified level.

Adaptive learning
The ECM “adapts” the “base line” idle fuel metering strategy as the engine “ages”.

Diagnostic monitoring
Sensor inputs and feedbacks are processed and used for diagnostic monitoring. Detected faults are logged in memory
as diagnostic trouble codes (DTCs); engine default strategies are implemented as dictated by the fault(s).

NOTES

Student Guide 2.7

JAGUAR EMS: CONTROL FUNDAMENTALS
Service Training

JAGUAR ENGINE MANAGEMENT SYSTEMS

Engine Control Module Outputs
ECM OUTPUTS

Fuel pump / fuel pressure

When the ignition is switched ON and the engine cranks, the ECM operates the fuel pump via the
fuel pump relay. Fuel pressure in the engine fuel rail is maintained within a specified pressure
range by a fuel pressure regulator that senses intake manifold vacuum.

Fuel injection
The fuel injectors are solenoid operated precision valves, which when activated, atomize gaso-
line. The ECM achieves the required air : fuel ratio by varying the fuel injector pulse duration
(length of time the injectors are activated). All fuel injectors are pulsed simultaneously, normally
once per engine revolution (twice per engine cycle).

Ignition
The ignition system employs a conventional distributor drive, rotor and cap for spark distribu-
tion. Spark timing is output from the ECM to an ignition module, which in turn switches the
ignition coil primary circuit and controls ignition dwell. Momentary timing retard provides
engine torque reduction for transmission shift quality enhancement.

Idle speed
The mechanical throttle body incorporates a motorized idle speed control valve and bypass air
ECM circuit. The ECM drives the idle speed motor open or closed to achieve the target idle speed. In
certain systems a supplementary air valve, driven by the ECM, is used to augment idle air flow at
low engine temperature.

Evaporative emission purge valve

The evaporative emission control system incorporates a charcoal canister, which absorbs fuel
vapors from the fuel delivery system while the engine is running. A solenoid operated purge
valve is driven by the ECM to open and allow the canister to be purged of vapor build-up by vent-
ing to the engine air intake system. Canister purge is controlled by the ECM from a programmed
strategy.

Exhaust gas recirculation

Exhaust gas recirculation (EGR) is used to lower combustion temperature during peak periods
thereby reducing the level of “oxides of nitrogen” (NOx) in the exhaust gas. Exhaust gas is
allowed to flow into the intake manifold by a solenoid operated vacuum solenoid valve driven by
the ECM. The ECM controls EGR from a programmed strategy.

2.8 Student Guide

JAGUAR EMS: CONTROL FUNDAMENTALS
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ECM OUTPUTS

Air injection
Air injection into the exhaust manifold is used to reduce the time necessary for the catalytic con-
verter to reach its operating temperature. When activated by the ECM, the engine driven air
pump clutch engages the pump and air flow commences. Simultaneously, the ECM opens a sole-
noid operated vacuum valve, which opens an air injection cut-off valve allowing air flow to the
exhaust manifold. The ECM controls air injection from a programmed strategy.
Certain engine management systems have air injection systems with electrically driven and con-
trolled air pumps replacing the engine driven pumps.

Engine speed limit

The ECM limits the maximum engine speed by fuel injection cut-off.

Engine default operation

Engine sensor input defaults are substituted by the ECM in the case of sensor signals faults. These
defaults allow the vehicle to be operated until the fault(s) can be repaired.

Transmission
The transmission control module receives engine speed, load and driver demand signals for use
in calculating transmission shift quality values.
ECM
Instrument pack
The instrument pack receives an engine speed and fuel used signals for tachometer and trip com-
puter operation. In the case of an OBD detected fault, the ECM provides the instrument pack
with a signal to illuminate the CHECK ENGINE malfunction indicator lamp (MIL).

Diagnostic data link

A serial data link and data link connector (DLC) allow technician interface with the ECM and the
transmission control module.

Student Guide 2.9

JAGUAR EMS: CONTROL FUNDAMENTALS
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JAGUAR ENGINE MANAGEMENT SYSTEMS

OBD Emission Compliance
Vehicle Model Engine ECM Version
Range Year Family Identification Enh.
I II Tier 0 Tier 1 TLEV LEV ULEV EVAP ORVR
XJ6 1990 - 94 AJ6 4.0 Lucas 15 CU X X
1995 - 97 AJ16 4.0 Sagem/Lucas X X X
GEMS 6
XJ8 1998 AJ26 4.0 Denso X X X X
1999 - 00 AJ27 4.0 Denso X X (99) X (00) X X
XJ12 1992 V12 5.3 Lucas 26 CU X X
1993 - 94 V12 5.3 Lucas-Marelli X X
1995 - 96 V12 6.0 Denso X X
XJR 1998 - 99 AJ26 (V8) SC 4.0 Denso X X X X
2000 AJ27 (V8) SC 4.0 Denso X X X X
XJS 1993 - 94 AJ6 (V6) 4.0 Lucas 15 CU X X
XJR-S 1993 V12 6.0 Zytec X X
XK8 1997 - 98 AJ26 (V8) 4.0 Denso X X X X (98)
1999 - 00 AJ27 (V8) 4.0 Denso X X (99) X (00) X X
XKR 2000 - AJ27 (V8) SC 4.0 Denso X X X X
S-TYPE 2000 - 01 AJ V6 3.0 PTEC X X (00) X (01) X X
AJ V8 4.0 PTEC X X (00) X (01) X X

Jaguar Engine Management Systems: Expanded Systems

Later developments in engine management control technology resulted in expanded Jaguar engine management sys-
tems. In addition to the earlier EMS control functions, expanded systems include the following:
• Electronic throttle control
• Fuel injection control with sequential fuel injection; air assisted fuel injection
• Ignition control – firing order; timing; dwell
• Ignition knock control
• Catalyst monitoring
• Variable valve timing
• Variable intake
• Enhanced evaporative emission control
• Cruise control
• Individual cylinder intervention
• ABS/TC interface
• Security interface
• Network communication

These systems are covered in detail in their respective course sections when you attend Jaguar Service Training Course
880 – V6/V8 Engine Management.

2.10 Student Guide

J A G U A R S E R V I C E T R A I N I N G

JAGUAR ENGINE MANAGEMENT SYSTEMS:

ON BOARD DIAGNOSTICS REVIEW

1 ON BOARD DIAGNOSTICS REVIEW

ON-BOARD
DIAGNOSTICS

Service Training Course 801S

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
z Service Training

NATIONAL LOW EMISSION VEHICLE PROGRAM

The California Air Resource Board (CARB) initiated the Low Emission Vehicle program mandating a staged reduc-
tion in vehicle emissions for vehicles sold in the state of California. The EPA adopted this strategy for national
compliance which became the National Low Emission Vehicle Program (NLEV).

The NLEV program has been used voluntarily by the northeastern states of the US to address increasing smog
problems. The NLEV program became law in 1999 and requires all vehicles sold in northeastern states comply
with the NLEV standards. Complete national phase in will be realized by 2004.

The NLEV program requires that vehicle manufactures reduce total emission levels through a series of stages over
a specified time period. The total number of vehicles a manufacturer schedules to build for the given year is also
factored into the equation. The stages of compliance for internal combustion engines are identified as:

TLEV = Transitional Low Emission Vehicle O

Grams per mile @ 50 F - (Cold engine start)
LEV = Low Emission Vehicle
ULEV = Ultra Low Emission Vehicle Compliance NMHC CO NOx
Level
The vehicle components and control systems must maintain TLEV 0.250 3.4 0.4
set emission levels through the life span of the vehicle LEV 0.131 3.4 0.2
(accumulated mileage).
ULEV 0.040 1.7 0.2
Tailpipe emissions are categorized as: Grams per mile @ 50,000 Miles

• NMHC = Non Methane Hydrocarbon Compliance NMHC CO NOx

Level
• CO = Carbon Monoxide
• NOx = Oxides of Nitrogen TLEV 0.125 3.4 0.4
LEV 0.100 3.4 0.3
Prior to the NLEV program the most stringent national com- ULEV 0.055 2.1 0.3
pliancy was Tier 1. The benefit of exhaust emission reduc-
tions that NLEV program provides compared with Tier 1 Grams per mile @ 100,000 Miles
standards are as follows:
Compliance NMHC CO NOx
Level
• TLEV - 50% cleaner TLEV 0.156 4.2 0.6
• LEV - 70% cleaner
• ULEV - 84% cleaner LEV 0.125 4.2 0.4
ULEV 0.075 3.4 0.4
OBD.01

Student Guide OBD.3

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Service Training

AUTOMOBILE EMISSION SOURCES

Tailpipe emissions are not the only contributor of pollutants from an automobile. The vehicle contributes to air
pollution by emitting Hydrocarbon based gasses identified as Non Methane Organic Gasses (NMOG) and Volatile
Organic Compounds (VOC). NMOG and VOC emissions are classified to stationary emission sources which escape
to atmosphere and contribute to poor air quality.

NMOG and VOC are released from a vehicle through evaporation and outgassing from the fuel system evaporative
system, evaporating engine oil, windshield washer fluid, paints and solvents. Gradual outgassing of petroleum
based vehicle components such as plastics, rubber materials and compounds also contribute to VOC generation.

OBD.02

The EPA has addressed outgassing or release of VOC to atmosphere by categorizing and mandating the following:

• Minimize generation of VOC outgassing caused by component materials.

• Running Loss Compliance (Integrate Non Return Fuel Systems).
• Monitor the vehicle evaporative system for leaks (OBD II Compliance).
• On-board Refueling Vapor Recovery (ORVR) Compliance.

The combination of the NLEV program and On Board Diagnostics results in a future national vehicle fleet that is
cleaner and has the capability of detecting and alerting the driver of mechanical and electrical malfunctions prior to
failure.

OBD.4 Student Guide

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ON BOARD DIAGNOSTICS I
A large portion of technology used in engine control systems is due to the legislative requirement of complying with
emission regulations to reduce air pollution. Engine control system self monitoring provides an alert system to the
driver in the event of a malfunction in the emission control functions of the system. The self monitoring capabilities
are called On Board Diagnostics.

The California Air Resources Board (CARB) established regulations for vehicles that would be sold in California
beginning with the 1988 model year. These regulations are known as On Board Diagnostics - version 1 (OBD I).
The Environmental Protection Agency (EPA) adopted the California program for all manufactures selling vehicles in
the US starting with the 1988 model year.

However, Jaguar vehicles did not have an instrument cluster check engine light until the 1990
model year. 1988 & 89 vehicles have the check engine light function incorporated with the CHECK
VCM. Diagnostic fault codes are also provided with the VCM. ENG
OBD I monitoring requirements included: OBD.03

• Correct function of the Engine Control Module (ECM)

• Fuel metering system
• Exhaust gas recirculation system
• Emission related components

To achieve this the OBD I system monitors all sensors used for fuel, EGR, and other emission controls for opens and
shorts in the components or their circuits. Fuel trim, EGR and oxygen sensors were also monitored for functionality.
Any malfunctions required:

• The Malfunction Indicator Light (MIL) to light while the malfunction was present.

• A Diagnostic Trouble Code (DTC) to be set in the Engine Control Module which is accessed with the PDU or
WDS.

• A procedure for activating flashing codes of the MIL to provide fault information to all technicians for diagno-
sis. This procedure is not necessary for Jaguar Dealers since the JDS/PDU/WDS are used for fault code access.

Visit the CARB web site @ http://arbis.arb.ca.gov/msprog/obdprog/obdprog.htm for more information on the
organization

Student Guide OBD.5

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ON BOARD DIAGNOSTICS II
Overview
In their continuing efforts to improve vehicle emission levels and on board monitoring capabilities, CARB imple-
mented a more stringent program for their state requirements know as On Board Diagnostics, version 2 (OBD II).

OBD II implements further refinements in the ability to monitor the proper function of a vehicle drivetrain ensuring
emission levels do not exceed accepted levels. Drivetrain systems that affect emission levels if impaired include:

• Engine Management
• Transmission Control
• Traction Control

The Environmental Protection Agency (EPA) adopted the CARB program and made it a federal requirement based
on the Clean Air Act amendment of 1990. The EPA required a complete phase in of OBD II compliance for all vehi-
cles sold in the US by 1996 model year. All Jaguar vehicles sold in the US were compliant by 1995.

The complete compliance document is titled, 1968.1 Malfunction and Diagnostic System Requirements. Visit the EPA
web site at www.epa.gov for detailed information.

In preparation of mandating OBD II, the EPA and CARB consulted the SAE (Society of Automotive Engineers) to
establish common standards for all vehicle manufactures ensuring consistency from one manufacture to the next.
These standards include:

• J 1930 - common acronyms of system components.

• J 1850 - common Diagnostic Equipment Communication Protocol.
• J 1962 - common Data Link Connector (DLC), and guidelines for its location in the vehicle.
• J 1978 - recommended practices for common OBD II Scan Tool
• J 1979 - common generic scan tool software.
• J 2190 - common Diagnostic Test Modes.
• J 2012 - common Diagnostic Trouble Codes.

The standards simplify diagnosis by mandating a common scan tool communication protocol and Data Link Con-
nector, accessing information, providing standard component names, test modes and diagnostic trouble codes
(DTCs) for all vehicles.

Visit the SAE web site at www.sae.org for detailed information on these standards.

OBD.6 Student Guide

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
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OBD II TERMS

When introduced, OBD II brought with it many new terms for service personnel to become familiar with. Knowing
what these terms mean is necessary in order to carry out diagnosis of vehicle systems. An overview of the terms
are provided on the following pages.

• Drive Cycle, Warm Up Cycle, Trip and the Federal Test Procedure (FTP) (See pages 8 & 9)
• MIL Activation Criteria (See pages 10 & 11)
• Data Link Connector (DLC) (See page 12)
• Diagnostic Trouble Codes (DTC) (See page 14)
• Readiness Codes (See page 15)
• Freeze Frame Data (See page 15)

OBD II MONITOR REQUIRMENTS

To facilitate the expanded monitoring requirements of OBD II, emission related vehicle systems require additional
software capabilities and components such as:

• Post catalytic converter oxygen sensors

• Fuel tank pressure sensor
• Evaporative Fuel System Shut off valve
• Differential Pressure Feedback EGR sensor

The additional components and software programming allows the Engine Control Module to comply with OBD II
regulations and monitor the following functions and systems:

• Comprehensive Component Monitor (See Page 17)

• Heated Oxygen Sensor Monitor (See Page 18)
• Catalytic Converter Efficiency Monitor (See Page 20)
• Engine Misfire Detection Monitor (See Page 22)
• Evaporative Emission Systems Monitor (See Page 25)
• Secondary Air Injection System Monitor (See Page 28)
• Fuel System Monitor (See Page 29)
• Exhaust Gas Recirculation System Monitor (See Page 30)
• Engine Coolant Thermostat Monitor (See Page 32)

Student Guide OBD.7

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Warm up, Drive Cycles & Trips

To conclusively test the function of an emission component or system function the vehicle must be operated under
varied running conditions which is known as a Drive Cycle. Segments of the Drive Cycle are also identified such as
Warm Up Cycle and Trip.

During the Drive Cycle the ECM activates the various emission systems to monitor their function. If faults are
detected during the monitoring stages, the ECM will store the event in its memory. If it happens a second time on
the next successive drive cycle, the driver is alerted via the CHECK ENGINE MIL.

Drive Cycle parameters are based on the Federal Test Procedure (FTP). The FTP is a set driving cycle established by
CARB that allows the engine to warm up and the vehicle to drive through varied engine speed and load conditions
ensuring the emission systems are activated and monitored.

Warm-up Cycle: operation of the vehicle to the point of warming the coolant by at least 40°F higher than the last
engine off and reaching at least 160°F.

Drive Cycle: takes the warm-up cycle one step further by operating the vehicle to the point whereby it will go into
closed loop control and include the operating conditions that are necessary to initiate or even complete a specific
OBD II monitor. These specific Drive Cycles are provided in the DTC summary publications.

Trip: Beginning with an engine off period, after the engine is started, the vehicle must travel a specified distance to
allow the following five OBD II monitors to complete all of their tests:

1. Misfires
2. Fuel System
3. Comprehensive components
4. EGR
5. HO2S

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OBD II Drive Cycle

This is a very specific combination of driving conditions that have been set out by the Federal Clean Air Act adher-
ing to Federal Test Procedure 75 (FTP 75). Completion of all the conditions of this cycle ensures that all monitors
have completed their required tests. This cycle is the most comprehensive of all the cycles.

FEDERAL TEST PROCEDURE 75 (FTP 75)

1 2 3 4 5 6 7 8 9 10 11 12 13
60

50
VEHICLE SPEED

40

30

20

10

IDLE
TIME
OBD.04

In order for all monitors to take place the following must happen:
Connect the Scan Tool or PDU to the DLC. Switch ignition on. Start the engine. Once started, the engine must not
be turned off at any time during the drive cycle.
1. Allow the engine to idle or drive the vehicle for at least 4 minutes until it is warmed up to a temperature of
180°F.
2. Idle for 45 seconds.
3. Accelerate to 45 MPH at 1/4 throttle (elapsed time is about 10 seconds).
4. Once 45 MPH is realized, decelerate vehicle speed to approximately 35 MPH
5. Drive at a speed between 30 and 40 MPH, maintaining a steady throttle position for at least one minute.
6. Decelerate to a speed above 20 MPH.
7. Drive until at least four minutes are spent between 20 and 45 MPH. Do not operate at WOT.
8. Decelerate and idle for at least 10 seconds.
9. Accelerate to 55 MPH at 1/2 throttle (elapsed time should be about 10 seconds).
10. Cruise at a speed between 45 and 55 MPH, maintaining a steady throttle position for at least 80 seconds. Do
not exceed posted speed limit.
11. Decelerate vehicle and stop.
12. Bring vehicle down to idle.
13. Check scan tool for on-board system readiness test results and any DTCs.

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Check Engine Light (MIL)

MIL activation changed with the introduction of OBD II. The MIL is activated when the ignition is switched to the
ON position before cranking which serves as a bulb check function of the instrument cluster.

The ECM determines the activation criteria of the MIL. It signals the ECM via the SCP or CAN
networks on to signal the instrument cluster starting with the 1997 model year vehicles. On CHECK
pre 97 models, the MIL is signaled on via a dedicated circuit. ENG
Illumination of the MIL is in accordance with the FTP which requires activation when: OBD.03

• A malfunction of a component that can affect the emission performance of the vehicle occurs and causes emis-
sions to exceed 1.5 times the standards required by the FTP.
• An OBD II monitored input signal is out of range, open or shorted (Comprehensive Component Monitoring).
• Misfire faults occur.
• A leak is detected in the evaporative fuel system.
• The oxygen sensors observe no purge flow from the purge valve/evaporative system.
• Engine control module fails to enter closed-loop operation within a specified time period.
• Engine or transmission control enters a limp home mode.
• Jaguar defined specifications are exceeded.

To prevent erroneous illumination, if a fault is detected once, it must also be detected a second time on the next
consecutive driving cycle. At the point in which the fault is conclusively confirmed in the drive cycle, the MIL is
then activated. However, faults that are monitored as catalyst damaging will cause the MIL to illuminate immedi-
ately.

OBD.05

Jaguar vehicle instrument clusters also inform the operator with additional information via RED and AMBER MILs
along with Message Center information. Refer to the DTC summary guides.

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The table illustrates example scenarios of when and how the MIL is activated (on and off) based on drive cycle fault
detection.

DRIVE CYCLE DRIVE CYCLE DRIVE CYCLE DRIVE CYCLE DRIVE CYCLE *DRIVE CYCLE
#1 #2 #3 #4 #5 # 43

FAULT CODE

FAULT CODE

FAULT CODE

FAULT CODE

FAULT CODE

FAULT CODE
FUNCTION

FUNCTION

FUNCTION

FUNCTION

FUNCTION

FUNCTION
MIL MIL MIL MIL MIL MIL

CHECKED

CHECKED

CHECKED

CHECKED

CHECKED

CHECKED

ERASED
STATUS STATUS STATUS STATUS STATUS STATUS
TEXT

SET

SET

SET

SET

SET
NO. CHECK
ENG
CHECK
ENG
CHECK
ENG
CHECK
ENG
CHECK
ENG
CHECK
ENG

1. YES YES OFF

2. YES YES OFF YES YES ON

3. YES YES OFF NO NO OFF YES YES ON

4. YES YES OFF YES NO OFF YES NO OFF YES YES OFF YES YES ON

5. YES YES OFF YES YES ON YES NO ON YES NO ON YES NO OFF

FAULT
6. YES YES OFF YES YES ON YES NO ON YES NO ON YES NO OFF YES ERASED
CODE OFF

OBD.06

1. A fault code stored in the control module upon the first occurrence of a fault in the system being checked.

2. The MIL will not be illuminated until the completion of the second consecutive driving cycle where the previ-
ously faulted system is again monitored and a fault is still present.

3. If the second drive cycle was not complete and the specific functions was not checked as shown in the example
the engine control module counts the third drive cycle as the next consecutive drive cycle. The MIL is illumi-
nated if the function is checked and the fault is still present.

4. If there is an intermittent fault present and does not cause a fault to be set through multiple drive cycles, two
complete consecutive drive cycles with the fault present are required for the MIL to be illuminated.

5. Once the MIL is illuminated it will remain illuminated unless the specific function has been checked without
fault through three complete consecutive drive cycles.

6. The fault code will also be cleared from memory automatically if the specific function is checked through 40*
consecutive drive cycles without the fault being detected or with the use of a scan tool, PDU or WDS.

* = With catalyst damaging faults it requires 80 consecutive drive cycles without the fault being re-detected
for the MIL to be switched off (or with scan tool, PDU/WDS).

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Data Link Connector (DLC)

To comply with SAE specification J 1962, the DLC has a standardized shape for connection with all generic scan
tools and the PDU/WDS.

Communication between the engine/powertrain control

1 2 3 4 5 6 7 8
modules and the diagnostic equipment is carried out via
specific communication ports in the DLC based on diag-
nosis or programming.

9 10 11 12 13 14 15 16

VEHICLE SIDE (FEMALE) OBD.07

PIN Description Application

1. Ignition Switch Ignition Switch Position II (RUN)

2. J1850 Communication Protocol SCP BUS (+)

3. Airbag Diagnostic Link Serial Communication for Airbag Diagnostics (XK Only)

4. Chassis Ground –

5. Signal Ground –

6. CAN_H CAN data link (high) (XK/XJ Only)

7. ISO-9141 Diag. Communication Diagnostic communication serial data link to vehicle modules All Models

8. Ignition Switch Ignition Switch Position I “ACC” (XK/XJ Only)

9. Battery Power (switched) Vehicle battery power via Ignition switch or Ignition Control (XK/XJ Only)
10. J1850 Common Protocol SCP BUS (–)

11. Vacant Not utilized at this time

12. Flash EEPROM (XK/XJ Only) Flash programming communication port

13. Flash EEPROM (XK/XJ) Flash programming power link (power supply to module for programming)

13. Flash EEPROM (S-TYPE) Flash programming communication port

14. CAN_L CAN data link (low) (XK/XJ Only)

15. ISO-9141 Diag. Comm. Diagnostic communication serial data link to vehicle modules (XK/XJ)

16. Battery Power Vehicle Battery power available at all times (unswitched)

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Generic Diagnostic Software and Scan Tool

To comply with SAE specifications J 1978 and 1979, OBD II compliant ECMs must be capable of communicating
with a generic OBD II diagnostic scan tool and software to provide commonality for all manufactures. This man-
dated requirement allows independent service shops the capability of diagnosing emission related faults without
purchasing manufacture specific proprietary equipment.

The generic scan tool software is divided into the following 6 modes:

Mode 1. Parameter Identification (PID), access to live data, digital and GDS 500E
analog values for inputs and outputs etc. This is similar to the Datalogger
feature of the PDU/WDS.

Mode 2. Freeze Frame Data Access. Snapshot of captured data for all
emissions related values at the time of a recognized fault.

Mode 3. This enables all scan tools to retrieve stored DTCs. The DTC can
be displayed alone or with descriptive text.

Mode 4. Ability to clear emission-related diagnostic information (DTCs

and Freeze Frame Data).

Mode 5. Monitoring of the Oxygen Sensors to determine Catalytic Con- OBD.08

verter Efficiency.

Mode 6. Provides activation of certain ECM output devices to selectively PDU

control certain outputs to determine real time functionality.

Jaguar Diagnostic Equipment

The Jaguar PDU/WDS are capable of performing all the mandatory func-
tions included in the six modes of diagnosis.

They also provide fault descriptions of Jaguar specific DTCs (P1XXX). This
is not a requirement of generic software.
OBD.09
The WDS also provides the following features not found on generic scan
tools:
WDS
• Manufacturer specific guided diagnostics
• Vehicle control system configuration
• Digital multimeter and dual trace oscilloscope
• Driveshaft balancer
• Vibration analyzer
• JTIS access

OBD.10

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OBD II Diagnostic Trouble Codes (DTC):

• SAE specification J 2012 established the Diagnostic Trouble Codes (DTC) used for OBD II systems.

• The DTCs are designed to be identified by their alpha/numeric structure.

• The SAE has designated the emission related DTCs to start with the letter “P” for powertrain related systems.

• Jaguar also follows the SAE convention for other non OBD II monitored systems such as Chassis and Body. Their
Alpha structure is identified “B” and “C” respectively.

• The source digit indicates that this particular code is one that will be found on all manufacturers products as
noted by the second digit is 0. When there is a 1 in this position, the code would be specific only to a Jaguar
specific component or function.

P - Powertrain P 0 3 0 7
B - Body
C - Chassis
Source:
0 - SAE
1 - Jaguar
System:
0 - Total System 4 - Auxiliary Emission Control
1 - Fuel/Air Metering 5 - Vehicle Speed & Idle Control
2 - Fuel/Air Metering 6 - Module Inputs/Outputs
3 - Auxiliary Emission Control 7 & 8 - Transmission
Sequentially numbered to identify individual fault (00-99) P12

Therefore the DTC P0307 indicates:

P- Powertrain problem
0 - SAE sanctioned
3 - Related to an ignition system/misfire
07 - The misfire has been detected at cylinder # 7.

The PDU and WDS are used to access all Jaguar vehicle system DTCs. A generic scan tool (i.e.: GDS 500E) can also
be used to access OBD II specific DTCs (SAE sanctioned only).

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Readiness Code
The readiness codes provide status (yes/no) of the system having completed all of the required monitoring func-
tions. Each OBD II required monitor displays “readiness” in the PDU Toolbox and with an aftermarket scan tool.
The code is binary (1/0).

0 = Test completed or Not Applicable, 1 = Test not completed.

The readiness code was established to prevent disconnecting the battery or clearing the fault memory to manipu-
late the results of the emissions test procedure.

Interpretation of the Readiness Code (SAE J1979)

• The complete readiness code is equal

to one byte (eight bits).
1 0 1 1 0 1 1 0
• Every bit represents one complete Catalyst Efficiency Monitor
test and is displayed by the scan tool,
Catalyst Heating (= 0, N/A at this time)
as required by CARB/EPA.
EVAP System Monitor
• When the complete, applicable Secondary Air Delivery Monitor
readiness codes equal 0 then all tests Air Conditioning Monitor (= 0, N/A at this time)
have been completed and the system 02 Sensor Monitor
has established its readiness (all mon- 02 Sensor Monitor
itors completed).
EGR Monitor
P13-1

System readiness via DTCs:

• System readiness is also displayed by

DTCs in the ECM fault memory. ECM System Readiness System Readiness
System Not Complete Since Complete Since
Last Memory Clear Last Memory Clear
• The DTCs are displayed with the
PDU, WDS or a generic scan tool Denso P1000 P1111
(i.e.: GDS 500). PTEC P1000 —
P13-2

Freeze Frame Data

When a DTC is logged, a freeze frame of engine operating
parameters are also memorized and available for display with FSS#1 ( # 1 )
the PDU/WDS or a generic scan tool.
FSS#2 ( # 2 )
This information is helpful for diagnosing what was occurring CLV . %
with the vehicle and its environment when the DTC was flagged.
*ECT
This information is also required when filling out the OBD II *STFT-B1 . %
Report form (see page 18).
*LTFT-B1 . %
*STFT-B2 . %
*LTFT-B2 . %
P13-3

Student Guide OBD.15

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OBD II Report Form

When servicing a vehicle with Engine or Transmission Control malfunctions, remember to fill out a OBD II Report
Form (S93). The form must be filled out with the pertinent information and sent to the Product Investigations
Department in Mahwah, New Jersey. Jaguar Cars pays 1/2 hour per individual form submittal.

• Fax number = 1 973-818-9763.

Record the applicable data on the form including the part number of the affected control module and the diagnos-
tic software currently loaded in your PDU/WDS. DTCs and FREEZE FRAME DATA must be extracted from the PCM,
ECM and/or TCM with the PDU/WDS or generic scan tool.

The data compiled from these forms provides a national focus on product technical issues and an expedited resolve
ultimately improving customer satisfaction.

OBD II REPORT S,93

Date of Issue: 3/2000 S,93 page 1 of ____

Dealer Name ___________________________________________ Dealer No. ___________________ Date ____________

OBD II Report ((continued
continued
continued))
VIN Mileage _____________________________________
Date of Issue: 3/2000 S,93 page 2 of ____

Engine Control Module (ECM) part no. Powertrain Control ModuleFREEZE

(PCM) part
FRAMEno. RECORD NUMBER ONE FREEZE FRAME RECORD NUMBER TWO

Field ref. Record Field ref. Record

Transmission Control Module (TCM) part no. PDU Software Issue no.
SUPP
SUPP SUPP
This work is being carried out because (check all applicable boxes the briefly describe the complaint
FCFF below): FCFF
The CHECK ENGINE MIL was illuminated. The TRANSMISSION MIL was illuminated.
FSS#1 ( # 1 ) FSS#1 ( # 1 )
Customer complaint — no MIL illuminated. Jaguar Cars Technical Services instruction
SS #2
FSS ( # 2 ) FSS
SS #2 ( # 2 )
The following DTCs (diagnostic trouble codes) have been logged in the ECM and / or TCM, or PCM. (check one)
CLV
CL . % CL
CLV . %
ECM TCM PCM
(Engine Control Module) (Transmission Control Module) (Powertrain Control Module)
*ECT ºC *ECT ºC
*STFT-B1
*STFT-B1 . % *STFT-B1
*STFT-B1 . %
*L
*LTFT
TFT-B1
-B1 . % *LTFT-B1
*LTFT-B1 . %
*STFT-B2
*STFT-B2 . % *STFT-B2
*STFT-B2 . %
*L
*LTFT
TFT-B2
-B2 . % *LTFT-B2
*LTFT-B2 . %
FRP KPa FRP KPa
IMAP
IMAP KPa IMAP KPa
RPM RPM RPM RPM
Record a brief description of the customer complaint and any additional information below.
VS km/h
km/h/ /MPH
MPH(circle
(circleone)
one) VS km/h / MPH (circle one)
______________________________________________________________________________________________________
IAT
______________________________________________________________________________________________________ ºC IAT ºC
MAF
______________________________________________________________________________________________________
MAF g/sec MAF g/sec
______________________________________________________________________________________________________ ATP
TP %
ATP
TP %
______________________________________________________________________________________________________
TPA
TP % TP
TPA %

From PDU, access FREEZE FRAME. AES

TAES s TAES
AES s
NOTE: More than one FREEZE FRAME record may be stored in memory. GP
GPA GPA
FR
Page through FREEZE FRAME and determine the number of FREEZE FRAMES that are stored inFRT
memory. ºC FR
FRT ºC
ERC ERC
Record the number of FREEZE FRAMES that are stored.

Record the FREEZE FRAME DATA in the appropriate fields of the following pages.
Write the TOTAL number of completed S,93 pages in the top right of each page.
Fax or copy and mail the completed report to Jaguar Product Investigations.

continued on next page

OBD.11

FORM DISTRIBUTION:

PRODUCT INVESTIGATIONS DEALER COPY

continued on next page

OBD.12

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Monitored Systems
Comprehensive Component Monitor

As part of the OBD II requirements, all engine management input and output control components are monitored
for shorts to power and ground and for open circuits. Additionally, engine management input signals are moni-
tored for plausible signal range.

The comprehensive component monitor is continual through each drive cycle.

Detected faults of this type are logged when first detected. On the next trip, if the fault is still present the fault is
logged and the MIL is illuminated.

– OBD.13

• Intake Air Temperature (P0112, P0113),

• Engine Coolant Temperature (P0117, P0118),
• Cylinder Head Temperature (P1289, P1290),
• Mass Air Flow (P0102, P0103)

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Oxygen Sensor Monitor

As part of the OBD II requirements, all oxygen sensors must be monitored for:

• electrically integrity (comprehensive component monitor)

• heater operation
• signal switching and response time.

Electrical Integrity: All oxygen sensors and their integrated heaters are monitored by the comprehensive compo-
nent monitor function of OBD II which includes detection of opens or shorts in the sensor/heater circuits and devi-
ations in the sensor’s ability to produce a plausible signal. The comprehensive component monitor is continual
through each drive cycle.

Heater Operation: All Heated Oxygen Sensors are also monitored for correct heater function. This monitor is
achieved through current monitoring when the heaters are switched on. The ECM performs this monitor once per
drive cycle.

An oxygen sensor heater fault is determined by turning the heater on and off and monitoring the corresponding
voltage change in the heater output driver in the ECM. A current monitoring circuit monitors the heater current
once per drive cycle. If the current does not exceed a predetermined value, the heater is assumed to be degraded
or malfunctioning.

ECM

MONITOR
O2 SENSOR
HEATING

MONITOR

OBD.14

Oxygen sensor signal switching time and response rate monitor:

The oxygen sensor signal is a direct correlation to sensed amount of oxygen in the exhaust gas. This input is
required to maintain accurate closed loop fuel injection and to monitor the efficiency of the catalytic converters
(post catalyst sensor).

As the sensors age or become contaminated, the speed at which they respond to changes in the detected oxygen
levels in the exhaust gas diminishes. To meet OBD II requirements, the ECM must determine if the sensor response
and switch rate is acceptable to maintain efficient oxygen monitoring.

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Switch Time Monitoring:

The transition (switching) time from lean to rich and rich to lean is measured and compared to a predetermined
value dependent on engine speed and air mass/load. A sampling of 10 signal switches is monitored and compared
to a predetermined time value to determine how quickly the sensor signal changes from lean to rich and rich to
lean.

Since switching time fluctuations can occur, the measured results are averaged over the total number of sampled
switches. If the maximum time value is exceeded, the fault is logged in the ECM. Whenever switching time is
again monitored and the maximum time value is again exceeded, the CHECK ENGINE MIL is illuminated and a
DTC is stored.

Switch time can also be affected by malfunctions in the fuel delivery system.

SWITCH TIME RESPONSE TIME

LEAN RICH
TO RICH TO LEAN
SIGNAL VOLTAGE

TIME
OBD.15

Response Time Monitoring:

The response rate of the oxygen sensor signal is also dependant on engine speed and load. For the ECM to deter-
mine that the oxygen sensor signal is cycling correctly, the length of time a signal remains at rest in either the lean
or rich condition is measured and compared with a predetermined value. If the maximum at rest threshold is
exceeded, the CHECK ENGINE MIL will be illuminate following the same criteria as with Switch Time Monitoring.

The typical monitor conditions are:

• Short term fuel trim (SHRTFT) is +/- 30%.

• Engine coolant temperature (ECT) is between 150˚ F (65.5 ˚C) and 240˚ F (115.5 ˚C).
• Intake air temperature (IAT) is less than 140˚ F (60 ˚C).
• Engine load is between 20 and 50 percent.
• Vehicle speed is between 30 MPH and 65 MPH.
• Engine rpm is between 1,000 and 2,200 rpm.
• Minimum time of 10 seconds in closed loop operation.

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Catalyst Efficiency Monitor

• The Catalyst Efficiency Monitor uses an oxygen sensor before and after a catalyst to confirm efficiency based on
oxygen storage capacity. Under normal closed-loop fuel conditions, catalysts have significant oxygen storage
which makes the switching frequency of the rear HO2S quite slow compared with the switching frequency of
the front HO2S.

• As catalyst efficiency deteriorates due to age, contamination or damage its ability to store oxygen declines and
the post-catalyst HO2S signal begins to switch more rapidly, approaching the switching frequency of the pre-
catalyst HO2S.
• In order to assess catalyst oxygen storage, the monitor counts upstream and downstream HO2S switches during
closed-loop fuel conditions after the engine is warmed-up and catalyst temperature is within limits.

INPUT: OUTPUT:
CO2 (Carbon Monoxide) N2 (Nitrogen)
HC (Hydrocarbon) H2O (Water)
NOx (Oxides of Nitrogen) CO2 (Carbon Dioxide)
O2 (Oxygen) O2 (Oxygen [trace amounts])

O2 O2
O2

O2 O2
O2

UPSTREAM OXYGEN STORAGE DOWNTREAM

OXYGEN SENSOR (CATALYST) OXYGEN SENSOR

OK NOT OK

RICH (LESS O2) RICH (VERY LITTLE O2) RICH (LESS O2)
VOLTAGE

VOLTAGE

VOLTAGE

LEAN (MORE O2) LEAN LEAN (MORE O2)

TIME TIME TIME
OBD.16

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• When the switch rate exceeds a threshold value (typically 0.75 switch ratio) during successive drive cycles, a
code is stored and the MIL illuminates.

• The catalyst efficiency is monitored once per trip while the vehicle is in closed loop operation. The evaluation
period of the sensor signals is performed over a predefined number of oscillation cycles.

• The catalyst monitoring process is stopped once the predetermined number of cycles are completed until the
next drive cycle.

• Refer to the DTC Summary Guide for troubleshooting procedures.

Catalyst Efficiency Monitor: Before the catalyst efficiency is monitored, the following conditions must be met:

• Oxygen sensor monitor completed and OK

• Evaporative System monitor completed and OK
• No DTCs stored for IAT, VSS, ECT, CPS and TP
• Intake air temperature between 20 and 180 degrees F.
• Part load throttle position
• Elapsed time since engine start up minimum 5.5 minutes
• Engine load minimum 10%
• Vehicle speed between 5 & 70 MPH

Student Guide OBD.21

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Misfire Monitor
To comply with OBD II regulations, the ECM must monitor for engine misfire events to prevent damage to the cata-
lyst and excessive tailpipe emissions. The ECM must also identify which cylinder(s) is/are causing the misfire and its
severity within two categories:

• Type A - Catalyst damaging (severe misfire)

• Type B - Emissions compliant relevant (mild misfire)

To achieve this, the ECM monitors crankshaft torque acceleration during the firing down stroke of each cylinder.
Misfires are detected by recognizing changes in the velocity of the crankshaft. Crankshaft velocity is determined by
measuring the amount of time it takes the crankshaft to travel a specified crank angle. Acceleration is the change in
velocity.

By comparing the crankshaft acceleration contributed by the combustion of each cylinder the Misfire Monitor can
determine if any of the cylinders are not producing the expected acceleration. A cylinder that lacks combustion
exhibits a lower acceleration compared to the others.

• To do this, the ECM divides the 360o crankshaft circumference into segments. It continually monitors engine
speed via the crankshaft position sensor and reluctor ring.

9 PULSES PER SEGMENT (ie: AJ27)

1 2 3 4

EXAMPLE:
RPM = 2800
Segment 1 = X ms time
Segment 2 = X ms time
Segment 3 = X+3 ms time
Segment 4 = X ms time
RELUCTOR RING
AND CRANKSHAFT MISFIRE CONSIDERED IN
POSITION SENSOR SEGMENT 3

OBD.17

• The sensor’s input pulses are counted and compared to a programmed time value for the given engine speed.
• If the combustion process in all cylinders is functioning correctly, the period duration for each segment is the
same.

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• During constant/stable engine speeds, if the period duration of one (or more) segment is detected as longer
than all the other segments, a cylinder specific misfire is “considered”. The measured time values are also cor-
rected based on engine load and engine temperature.

• Additionally, the ECM evaluates the suspect misfiring event for noise. Mechanical noise, such as rough road
conditions derived from ABS/IVD road speed sensor frequency irregularities or high rpm/light load conditions,
will produce piston acceleration variations. Misfire events of this type are considered noise. Noise-free deviant
acceleration exceeding a given threshold is labeled a misfire.

• If the expected period duration is greater than the permissible programmed value, and noise is conclusively fac-
tored out, the ECM will set a misfire DTC and illuminate the MIL based on the misfire severity; (Type A) or
(Type B).

Type A Misfires (Catalyst damaging)

• Evaluation of Type A misfires are concluded within 200 crankshaft revolutions. At the end of the evaluation
period, the total misfire rate and the misfire rate for each individual cylinder is computed. The monitor com-
pares the actual percentage of misfires to a threshold percent obtained from a speed/load table.

• If the misfire percentage is above the threshold and the catalyst temperature model indicates that the catalyst is
being damaged, the MIL blinks at a rate of once per second while the misfire is present.

• For XK and XJ vehicles through model year 1997, the MIL flashes when a Type A catalyst
damaging misfire is present on the first drive cycle and the MIL will stay on.

• Starting with 1998 model year, the regulations changed to allow the Misfire Monitor to CHECK
act like all other OBD II monitors. This means that the MIL will still flash but does not ENG
stay on until there is a fault on the second drive cycle. This regulation change was
intended to reduce MIL illumination due to unrepeatable misfires.

• S-TYPE vehicles follow the 1998 regulations. These systems will also inhibit fuel injection on up to two mis-
firing cylinders to prevent catalyst damage. The PCM reactivates injection for the misfiring cylinders during
the drive cycle to see if the condition was still exists.

Type B Misfires
Evaluation of Type B misfires are concluded within 1000 crankshaft revolutions. At the end of the evaluation
period, the monitor then compares the actual percentage of misfires to a threshold value. If the percent misfire is
above the emission threshold value, the MIL is illuminated on the second drive cycle.

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Misfire detection is an ongoing monitor that continues through the entire driving cycle.

The following conditions must be met for the misfire monitor to start:

• No DTCs stored for CKP or CMP

• Elapsed time since engine start up between 0 and 5 seconds.
• Engine temperature between 20 and 250 degrees F.
• Engine RPM range between idle and 2500.

The Misfire Monitor can be temporarily disabled for select conditions including:

• Closed throttle deceleration (see reluctor ring adaptation).

• Traction Control Regulation
• Rough Road Recognition
• Fuel cutoff due to vehicle speed or engine rpm limiting mode.

Reluctor Ring Adaptation

The ECM must also ‘learn’ and correct for mechanical irregularities in the reluctor
ring gap spacing when the engine is new or when the control module has been dis-
connected. Slight irregularities are detected and learned.

The learning process requires three 60 to 40 MPH closed throttle engine decelera-
OBD.18
tions with out applying the brakes. The learned corrections improve the high-rpm
capability of the monitor. The misfire monitor is not active until a profile has been
learned to prevent erroneous MIL activation.

Service Note. If the reluctor ring (torque converter flex plate/ starter ring gear) is replaced, disconnect the power
source to the ECM to clear the existing learned values.

OBD.24 Student Guide

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
z
Service Training

EVAP System Monitor

OBD II regulation requires monitoring the function of evaporative system purging and the sealed integrity of the
entire fuel system (evaporative system leak diagnosis).

Purge Flow Monitoring

The ECM detects purge flow two ways: if closed loop fuel metering indicates a large correction when purge is
enabled, or if the idle air control valve corrects for increased air flow when purging is enabled, the ECM has confir-
mation that purging is taking place.

If, during these functional conditions, the additional air introduced into the system is not detected on successive
drive cycles, the ECM will flag a DTC and illuminate the MIL.

INTAKE
MANIFOLD

VENT
FILTER

PURGE FLOW PURGE FLOW

EVAPORATIVE
CANISTER
CLOSE VALVE EVAPORATIVE MANIFOLD VACUUM
CANISTER
PURGE VALVE

SINGLE DUAL
EVAPORATIVE EVAPORATIVE
CANISTER CANISTER
PWM PURGE
CONTROL
STRATEGY
FUEL TANK PRESSURE OBD II
FUEL TANK LEAK
GRADE VENT PRESSURE CHECK
VALVE SENSOR

POWERTRAIN
CONTROL MODULE

FUEL TANK
OBD.19

Student Guide OBD.25

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
zService Training

EVAP System Leak Check Monitoring

The evaporative system leak test is done in four phases:
Phase 1 - Initial vacuum pulldown:
• The test starts out with a closed Evaporative Purge Valve. The ECM goes into open loop injection and closes the
Canister Close Valve to seal the system from ambient air. The ECM monitors a slight generation of vapor in the
system via the Fuel Tank Pressure Sensor. The slight positive pressure value is recorded.
• The EVAP purge valve is opened to pull a vacuum on the system. The ECM detects the vacuum via the Fuel
Tank Pressure Sensor input. The rate at which the vacuum signal changes is based on fuel tank level and must
be within a predetermined value.
• If the sensor signal does not change or is very slight, the ECM determines a large system leak which is most
likely caused by a fuel cap that was not installed properly, disconnected or kinked vapor lines (intake side of
purge valve), a Canister Close Valve that is stuck open or a purge valve that is mechanically stuck closed.
• If the vacuum signal is excessive, a vacuum malfunction is indicated. This could be caused by kinked vapor
lines (EVAP system side of purge valve) or the purge valve is stuck open.
Phase 2 - Vacuum stabilization, hold and decay:
• If the target vacuum signal is achieved in phase 1, the EVAP purge valve is closed and vacuum is allowed to sta-
bilize. This initial vacuum signal is noted in memory.
• Next, the vacuum is held for a calibrated time and the vacuum level is again recorded at the end of this time
period. The starting and ending vacuum signals are compared to determine if the change in held vacuum
exceeds the test criteria.
• The monitor will abort if there is an excessive change in load, fuel tank pressure or fuel level input since these
are all indicators of fuel tank instability (fuel slosh). If the monitor aborts, it will attempt to run again once con-
ditions are detected as stable.
• If the vacuum bleed-up is not exceeded, the small leak test is considered a pass.
• If the vacuum bleed-up is exceeded on two successive monitoring events, a 0.040” dia. leak is likely and a final
vapor generation check is done to verify the leak, phases 3-4.
Phase 3 - Vacuum release:
The vapor generation check is done by opening the canister close valve to release the stored vacuum.
Phase 4 - Vapor generation:
The pressure is monitored over a short period of time to determine if tank pressure remains low or if it rises due to
excessive vapor generation. If the pressure rise due to vapor generation is above the threshold limit for absolute
pressure and change in pressure, a P0442 DTC is stored.

EVAP System Leak Check Monitor Diagnostic Preconditions

Before the system is tested, the following conditions must be met:
• Oxygen sensor monitor completed and OK
• No DTCs stored for MAF, IAT, VSS, ECT, CKP and TP
• More than six hours elapsed time since completion of last drive cycle.
• Fuel level between 15% & 80%.
• Intake air temperature between 40° and 110° F.
• Vehicle elevation no higher than 8,000 feet.
• Elapsed time since engine start up between 5.5 and 30 minutes
• Engine load between 20% and 70%.
• Vehicle speed between 40 & 70 MPH

OBD.26 Student Guide

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
z
Service Training

OBD.20

Evaporative System Leak Troubleshooting

When a leak is confirmed via DTC, use the evaporative system

leak tester to determine the location of the leak on the vehicle.

• Refer to TSB 05.1-29 for complete instructions.

OBD.21

Student Guide OBD.27

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
zService Training

Secondary Air Monitor (AIR) – AJ 16 & 6.0 Liter V12 Engines Only
To reduce exhaust gas emission pollutants, the Secondary Air Injection system is required on the AJ 16 and 6.0 liter
V12 engines during cold start conditions. When cold, fuel injector on time is increased providing cold start enrich-
ment to start the engine. However, the rich mixture contributes to high levels of hydrocarbons during warm up.

Secondary air injection;

• accelerates oxidation of hydrocarbons during cold start
• reduces catalytic converter warm up time (light off achieved earlier)

The secondary air injection system adds air to the hydrocarbon enriched exhaust gas ensuring its continued com-
bustion.

AIR PUMP
This quickly heats the catalyst
up as the burning gas mixture
flows through the catalytic
converter.

To comply with OBD II regula- CHECK

VALVE
AIR CLEANER

tions, the secondary air injec-

tion system is monitored for
proper function.

The ECM monitors the sys-

tem’s electrical integrity
through comprehensive com- AIR PUMP
RELAY
ponent monitoring. It also 12V DC
ECM
confirms that air is actually
injected into the exhaust sys-
tem via oxygen sensor feed-
OBD.22
back during normal operation.

To perform this monitoring function, the ECM switches to open loop fuel injection. The oxygen sensors provide a
stable rich signal. The air injection system is activated on. The ECM monitors the oxygen sensor signals and when
a shift to lean is detected, the ECM confirms the system is functioning correctly.

Later Jaguar engines (AJV8 and V6) achieve fast catalyst light off through an ignition timing emission reduction strat-
egy during cold start conditions. In addition, catalyst locations are close to hot exhaust exiting the engine exhaust
parts. Therefore, these vehicles do not require the secondary air injection system.

OBD.28 Student Guide

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
z
Service Training

Fuel System Monitor

Fuel System monitoring is an OBD II requirement which monitors the calculated fuel injection on time in relation to
engine speed, load and the upstream oxygen sensor signals.

• The ECM uses the upstream catalyst oxygen sensor signals to provide closed loop injector control (except AJ16).

• The fuel system monitor determines the fuel

delivery needed (long/short term fuel trim). ENGINE CONTROL MODULE

• If components change beyond normal limits LONG TERM MEMORY

or if a malfunction occurs, the long term fuel

ENGINE LOAD
trim will reach a limit. BASE
FUEL INJECTION
RATES
• If too much or not enough fuel is delivered
over a predetermined time frame during the ENGINE SPEED
drive cycles, a DTC is set and the MIL is
SHORT TERM MEMORY
turned on.
OXYGEN
SENSOR
INFLUENCE
• Long term fuel trim corrections at their limits = INJECTION TIME
in conjunction with a calibrateable deviation
in short term fuel trim, indicate a rich or lean INTAKE
fuel system malfunction. AIR MASS

Fuel System Monitoring: The fuel system moni-

OXYGEN
tor is continuous while in closed loop fuel control. SENSOR
SIGNAL(S)
Additionally, the following conditions must be
met:
ENGINE SPEED

• Fuel system pressure sensor OK (PTEC)

• Engine speed between idle and 4,000 RPM
• Air Mass Range between .75 and 8.0 lbs per
minute. ADAPTION OF
INJECTION TIME DURATION
• Evaporative Purge not active
OBD.23
Typical Fuel Monitor malfunction thresholds:

Lean malfunction: Long Term Fuel Trim (LTFT) > 25%, Short Term Fuel Trim (STFT) > 5%

Rich malfunction: Long Term Fuel Trim (LTFT) < 25%, Short Term Fuel Trim (STFT) < 10%

Student Guide OBD.29

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
z
Service Training

Exhaust Gas Recirculation (EGR) System Monitor

EGR System monitoring is an OBD II requirement which monitors a series of electrical tests and functional tests for
EGR system operation. Jaguar vehicles have various types of EGR systems depending on the vehicle. For example:

• AJ16 = Electrically operated and monitored system.

• V6 PTEC = Electrically regulated Vacuum operated system/electrically monitored.

The EGR OBD II monitor overview presented here is based on the V6 PTEC system.

Comprehensive Component Monitor:

• First, comprehensive component monitoring for the Differential Pressure Feedback EGR
(DPFE) sensor input circuit is checked for out of range values (P1400 P1401).

• The Electronic Vacuum Regulator (EVR) output circuit is checked for opens and shorts
(P1409). OBD.24

Hose Monitor:

• After the vehicle is started, during vehicle acceleration, the differential pressure indicated by the DPFE sensor at
zero EGR flow is checked to ensure that both hoses to the DPFE sensor are connected. Under this condition, the
differential pressure should be zero.

• If the differential pressure indicated by the DPFE sensor exceeds a maximum threshold or falls below a mini-
mum threshold, an upstream or downstream DPFE hose malfunction is indicated (P1405 P1406).

EGR VALVE
DPFE SENSOR
EGR VACUUM
REGULATOR VALVE

EXHAUST GAS
FLOW

ORIFICE

OBD.25

OBD.30 Student Guide

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
zService Training

Flow Monitor:

• After the vehicle has warmed up and normal EGR rates are being commanded by the PCM the Flow flow check
is performed. Since the EGR system is a closed loop system, the EGR system will deliver the requested EGR flow
as long as it has the capacity to do so.

• If the EVR duty cycle is very high (greater than 80% duty cycle), the differential pressure indicated by the DPFE
sensor is evaluated to determine the amount of EGR system restriction. If the differential pressure is below a
calibrated threshold, a low flow malfunction in indicated (P0401).

Valve Mechanical Monitor:

• Finally, the differential pressure indicated by the DPFE sensor is also checked at idle with zero requested EGR
flow to perform the high flow check.

• If the differential pressure exceeds a calibrated limit (>0.6 volt compared with initial key on at start of current
drive cycle) it indicates a stuck open EGR valve or debris temporarily lodged under the EGR valve seat (P0402).

Before each of the tests are performed, the following conditions must be met:

Comprehensive Component Monitor:

• EGR system must be active with no faults

Hose Check:
• EVR Duty Cycle 0%
• Mass air flow maximum 8 lb/min.

Flow Check:
• EVR duty cycle between 80% and 100%.
• Engine Speed 2500 RPM maximum
• Maximum 6% deviation in intake air mass
• Manifold vacuum between 6 and 10 in hg.

Valve Mechanical Check:

• EVR duty cycle at 0%.

Student Guide OBD.31

JAGUAR EMS: ON BOARD DIAGNOSTICS REVIEW
z
Service Training

Thermostat Monitoring

• OBD II regulations require the ECM to monitor the mechanical function of the engine cooling system thermo-
stat beginning with the 2000 MY.

• The thermostat is considered malfunctioning if the engine does not warm-up in a predictable manner, as mon-
itored from the engine coolant temperature (ECT) sensor or the cylinder head temperature (CHT) sensor signals.

• A timer is counted while the engine is at moderate load or greater and the vehicle is moving. The target/mini-
mum timer value is based on ambient air temperature at start-up. If the timer exceeds the target time and ECT/
CHT has not warmed up to the target temperature, a malfunction is indicated.

• The test runs only after a 2 hour engine-off soak time, in order to permit engine coolant temperature to drop
below the target warm-up temperature on a hot engine.

• The target temperature is calibrated to the thermostat regulating temperature minus 20°F,
(i.e: 195°F rated thermostat = 175°F calibrated warm up temperature.)

OBD.32 Student Guide

AJ16 4.0 Liter Engine Management System

Contents

Overview 2

Engine Control Module (ECM) 3–4

EMS Component Location 6–8

ECM Pin Out Information 9

Fuel Delivery and Evaporative Emission Control 10 – 21

Fuel Injection 22 – 24

EMS Main Sensing Components 25 – 31

Ignition Control 32 – 37

Idle Control 38 – 41

Secondary Air Injection 42 – 44

Exhaust Gas Recirculation (EGR) 45 – 47

Catalytic Converters 48

Engine Misfire 49

Vehicle Systems Interfaces 50 – 51

On-Board Diagnostic Facility – OBD II 52 – 53

Engine Supercharger 54 – 57

Crankcase Emission Control 58

DTC Summary – 1995 Model Year 59 – 67

DTC Summary – 1996 Model Year ON 69 – 80

1
AJ16 4.0 Liter Engine Management System

Overview
The AJ16 Engine Management System (EMS) is controlled through a digital Electronic Control Mod-
ule (ECM) containing a microprocessor. The system maintains optimum performance over the engine
operating range by precisely controlling all fuel injection, ignition and emission control functions. In
addition, the ECM provides various interface outputs and incorporates an on-board diagnostic facility.

The AJ16 EMS complies with OBD II (on-board diagnostics II), the second generation environmental
legislative regulations that set the acceptable maximum level of motor vehicle exhaust emission and
the required engine control systems self diagnosis capabilities.

The previous EMS used on the AJ6 4.0 liter engine complied with OBD I, which required that the
following performance and diagnostic standards be met:

OBD I (AJ6 EMS 1990 – 94 MY)

• Exhaust emission level
• Monitoring and diagnosis of electrical fuel system faults
• Monitoring of both open and closed circuit faults
• Visual warning to driver: MIL (CHECK ENGINE)
• Fault code provided to technician: Diagnostic Trouble Code — DTC (Fuel Fail Code — FF)
and Flash Code output of the MIL

OBD II requires lower exhaust emission levels, standardized diagnostics and failure prediction.

OBD II (AJ16 EMS)

• Exhaust emission level reduced
• Industry standardized DTCs
• Generic (after-market) scan tool capable of DTC retrieval
• Expanded self diagnostics to include monitoring and diagnosis of any power train system fault
that will likely cause exhaust emission to exceed 1.5 times the standard level.
• Failure prediction of subsystems by performance observation over the life of the power train
including: catalyst efficiency, engine misfire, exhaust gas recirculation, and secondary air injection.

NOTES

2
 AJ16 4.0 Liter Engine Management System

Engine Control Module (ECM)

GEMS 6 Engine Control Module
The AJ16 EMS is microprocessor based using a Sagem / Lucas GEMS 6 ECM as the heart of the
system. The ECM has a 1.5 megabyte memory with a microprocessor running at a clock speed of 12/
24 MHz. The ECM uses discrete components plus analog-to-digital circuits to interface between the
microprocessor, the input sensors and the output devices. Software is programmed into two EPROMs
and one EEPROM. The EPROMs are used for control and data. The EEPROM is used for On-Board
Diagnostics and adaptive functions. The ECM has nonvolatile memory so that on-board diagnosis and
adaptive information is maintained if the vehicle battery is disconnected.

CAUTION: ECMs must not be switched from one vehicle to another, because fuel meter-
ing, idle air adaptions and the VIN cannot be reprogrammed using PDU.

The ECM contains two double sided printed circuit boards. One is a low power board and the other
is a high power board. The red and black 36-way connectors are therefore referred to as the low and
high power connectors respectively. Most of the input signals from engine mounted sensors, and
interfaces with other systems, are located on the low power (red) connector. The high power connec-
tor (black) mainly serves outputs such as fuel injector drive, ignition coil drive, and relay activation.

The expanded capacity of the ECM is used to store emission control strategies, diagnostics, semi-sequen-
tial fuel injection, and direct ignition. Sixty percent of the ECM software is used for OBD II diagnostics.

An ECM controlled relay remains energized for approximately 15 seconds after power-down. This action
enables the ECM to perform idle air control valve positioning and other initializing functions, yet allows for
reduced quiescent drain after switch-off.

ECM Monitoring for OBD II

GEMS 6 ENGINE CONTROL MODULE

HIGH POWER SIDE LOW POWER SIDE

(BLACK) (RED)

T801/1.01

On each power-up, the ECM runs an internal EEPROM check. If a retrieved parameter does not cor-
respond to what the ECM knows to be a serviceable value, a fault is present and the CHECK ENGINE
MIL will immediately be activated.

NOTES

3
4
EVAPORATIVE
CANISTER
FUEL PUMP RELAY

ECM PRESSURE CONTROL ECM

VALVE
FUEL LEVEL SENSOR

EVAPP
FUEL
PUMP
ECM
FUEL TANK PRESSURE
FILTER REGULATOR

FUEL RAIL ECM

ECM
ECM
IACV
MAFS
FI
ON PLUG
ECM COIL
TPS
HO2S
(UPSTREAM)
EGRT IATS
AIRP SENS.
EGRV
KS
CATALYST ECM
ECM ECM ECM
ECM
KS ECM ECM
ECM
HO2S
(DOWNSTREAM) ECTS
CMPS

CKPS
FUEL
PUMP ECM
CONTROLLED
AJ16 4.0 Liter Engine Management System

RELAY
ECM ECM FUEL IGNITION
EXHAUST AIRP SWITCHED
MANIFOLD PUMP
KEY TO ACRONYMS: RELAY POWER
AIRP SECONDARY AIR INJECTION PUMP
CKPS CRANKSHAFT POSITION SENSOR
CMPS CAMSHAFT POSITION SENSOR TRANSMISSION
Engine Control Module (ECM) (continued)

SENSORS (TORQUE CONTROL)

ECM ENGINE CONTROL MODULE
FUEL INJECTORS TRANSMISSION
ECTS ENGINE COOLANT TEMPERATURE SENSOR (THROTTLE POSITION)
EGRT SENS. EGR TEMPERATURE SENSOR IGNITION TRANSMISSION
Engine Management Logic: Normally Aspirated Engines

EGRV EGR VALVE (GEAR SELECTOR POSITION)

EVAPP EVAPORATIVE EMISISON CONTROL (PURGE) VALVE IDLE SPEED CLIMATE CONTROL
(A/C COMPRESSOR CLUTCH OPERATION)
FI FUEL INJECTOR EGR
HO2S HEATED OXYGEN SENSOR SERIAL COMMUNICATIONS
EVAPORATIVE PURGE
IACV IDLE AIR CONTROL VALVE
VEHICLE SYSTEMS INTERFACE
IATS INTAKE AIR TEMPERATURE SENSOR FUEL LEVEL (VEHICLE SPEED, ENGINE SPEED)
KS KNOCK SENSOR
OBD II MONITORING CHECK ENGINE
MAFS MASS AIR FLOW SENSOR
TPS THROTTLE POSITION SENSOR
ENGINE CONTROL MODULE

T801/1.02
 FUEL PUMP RELAY 1 EVAPORATIVE
CANISTER
FUEL PUMP RELAY 2

ECM PRESSURE CONTROL ECM

VALVE
FUEL LEVEL SENSOR

EVAPP
FUEL FUEL
PUMP 1 PUMP 2
ECM
FUEL TANK PRESSURE
FILTER REGULATOR
BYPASS VALVE AND
FUEL RAIL BYPASS VALVE ECM
ECM ACTUATOR
ECM
IACV
MAFS
FI
ON PLUG
ECM COIL
TPS
HO2S
(UPSTREAM)
EGRT SUPERCHARGER IATS
AIRP EGRV SENS.
KS
CATALYST ECM
ECM ECM
ECM
ECM 1996 MY ON
KS ECM ECM
ECM
HO2S
(DOWNSTREAM) ECTS FUEL FUEL
PUMP 1 PUMP 2
CMPS
Engine Management Logic: Supercharged Engines

CKPS FUEL FUEL

PUMP PUMP
RELAY 1 RELAY 2
ECM
CONTROLLED
RELAY
ECM ECM FUEL PUMP IGNITION
EXHAUST AIRP SWITCHED
MANIFOLD CONTROL
MODULE POWER
KEY TO ACRONYMS:
ENGINE
AIRP SECONDARY AIR INJECTION PUMP SPEED
CKPS CRANKSHAFT POSITION SENSOR
TRANSMISSION
CMPS CAMSHAFT POSITION SENSOR SENSORS (TORQUE CONTROL)
ECM ENGINE CONTROL MODULE TRANSMISSION
FUEL INJECTORS
ECTS ENGINE COOLANT TEMPERATURE SENSOR (THROTTLE POSITION)
EGRT SENS. EGR TEMPERATURE SENSOR IGNITION TRANSMISSION
(GEAR SELECTOR POSITION)
EGRV EGR VALVE IDLE SPEED CLIMATE CONTROL
EVAPP EVAPORATIVE EMISISON CONTROL (PURGE) VALVE (A/C COMPRESSOR CLUTCH OPERATION)
EGR (1996 MY ON)
FI FUEL INJECTOR
SERIAL COMMUNICATIONS
HO2S HEATED OXYGEN SENSOR EVAPORATIVE PURGE
IACV IDLE AIR CONTROL VALVE VEHICLE SYSTEMS INTERFACE
FUEL LEVEL (VEHICLE SPEED, ENGINE SPEED)
IATS INTAKE AIR TEMPERATURE SENSOR
KS KNOCK SENSOR OBD II MONITORING CHECK ENGINE
MAFS MASS AIR FLOW SENSOR
TPS THROTTLE POSITION SENSOR ENGINE CONTROL MODULE

T801/1.03

5
AJ16 4.0 Liter Engine Management System
AJ16 4.0 Liter Engine Management System

EMS Component Location

Normally Aspirated Engines: Sedan Range

1 2 3 4 5 6 7

8
19

18 9
17 10
17 11

12

15 16 15 14 13

KEY TO ILLUSTRATION
(ALSO APPLIES TO ILLUSTRATION AT RIGHT)
1 FUEL LEVEL SENSOR 13 EMS MAIN RELAY
2 EVAPORATIVE CANISTER 14 CRANKSHAFT POSITION SENSOR (CKPS)
3 INERTIA SWITCH 15 KNOCK SENSOR (KS)
4 SPARK PLUG WITH INTEGRAL COIL 16 THROTTLE POSITION SENSOR (TPS)
5 FUEL INJECTOR (FI) 17 UPSTREAM HEATED OXYGEN SENSOR (HO2S)
6 EGR VALVE (EGRV) 18 ENGINE CONTROL MODULE (ECM)
7 FUEL PRESSURE REGULATOR 19 TRANSMISSION CONTROL MODULE
8 MASS AIR FLOW SENSOR (MAFS) 20 EGR TEMPERATURE SENSOR (EGRT SENSOR)
9 EVAPORATIVE EMISSION CONTROL VALVE (EVAPP) 21 ENGINE COOLANT TEMPERATURE SENSOR (ECTS)
10 SECONDARY AIR INJECTION PUMP (AIRP) 22 DOWNSTREAM HEATED OXYGEN SENSOR (HO2S)
11 CAMSHAFT POSITION SENSOR (CMPS) 23 CATALYST
12 GENERATOR 24 IDLE AIR CONTROL VALVE (IACV)

T801/1.04A

6
 AJ16 4.0 Liter Engine Management System

6 20 7

10

21

11

4 21 10

11

14

22 23 17
10 14 15 16 24 15 5

T801/1.04B

7
AJ16 4.0 Liter Engine Management System

EMS Component Location

XJS Range (where different from Sedan Range)

EVAPORATIVE CANISTER

ENGINE CONTROL MODULE

TRANSMISSION CONTROL
MODULE (COUPE)

TRANSMISSION
CONTROL MODULE
(CONVERTIBLE)

T801/1.04C

8
 AJ16 4.0 Liter Engine Management System

ECM Pin Out Information

ENGINE CONTROL MODULE

25 36
HIGH POWER 12 1 13 24 LOW POWER
(BLACK) 24 13 1 12 (RED)
36 25

T801/1.01

ECM Black Connector A (High Power) ECM Red Connector B (Low Power)
1 Power ground – input 1 Intake air temperature – input
2 Fuel injector 1 – output 2 Not used
3 Idle speed control 1 – output 3 EGR valve function – input
4 Oxygen sensor heaters, downstream – output 4 Mass air flow (load) – input
5 Ignition coil 4 – output 5 Not used
6 Ignition coil 3 – output 6 Oxygen sensor 3 – input
7 Air pump – output 7 Sensor 5v ground – input
8 Ignition coil 2 – output 8 Oxygen sensor signal ground – input
9 Ignition coil 5 – output 9 Knock sensor ground – input
10 Ignition coil 1 – output 10 Bidirectional serial communication – input / output
11 Ignition coil 6 – output 11 Sensor 5v supply – output
12 Power ground – input 12 Throttle position – input

13 Fuel injector 4 – output 13 Not used

14 Fuel injector 3 – output 14 Engine coolant temperature – input
15 Fuel injector 2 – output 15 EGR valve position – input
16 Idle air control 2 – output 16 Oxygen sensor 1 – input
17 Fuel used – output 17 Battery voltage common supply – input
18 ECM controlled relay – output 18 Oxygen sensor 2 – input
19 Fuel pump – output 19 Oxygen sensor 4 – input
20 MIL – output 20 Fuel tank level – input
21 A/C compressor relay – output 21 Knock sensor A – input
22 Engine speed – output 22 Not used
23 Crankshaft position sensor positive – input 23 Not used
24 ECM controlled relay – input 24 Camshaft position sensor 12v supply – output

25 Fuel injector 6 – output 25 Not used

26 Crankshaft position sensor negative – input 26 Transmission ignition control – input
27 Fuel injector 5 – output 27 Park / neutral position – input
28 Idle speed control 4 – output 29 Mass air flow sensor ground – input
30 Oxygen sensor heaters, upstream – output 30 Small signal ground – input
31 Not used 31 Engine coolant temperature sensor ground – input
32 Throttle position (transmission) – output 32 Knock sensor B – input
33 Engine torque – output 33 Ignition ON – input
34 Evaporative emission control valve – output 34 Camshaft position – input
35 EGR valve – output 35 Not used
36 Power ground – input 36 Air conditioning ON request

9
AJ16 4.0 Liter Engine Management System

Fuel Delivery and Evaporative Emission Control

AJ16 FUEL DELIVERY AND EVAPORATIVE EMISSION CONTROL SYSTEM

EVAPORATIVE FUEL
ROLL-OVER FLANGE
VALVE INJ.

FUEL RAIL
INTAKE
MANIFOLD

JET CHECK
PUMP VALVE FUEL
PRESS.
SURGE
(CHECK VALVE REG.
POT
LOCATION VARIES
XJ6 – XJS)

FUEL TANK FUEL PUMP FUEL PUMP

1 2
(SC ONLY) FILTER

PRESSURE
CONTROL VALVE
(ROCHESTER
VALVE)
RESTRICTOR

EVAPORATIVE
VALVE
(NORMALLY CLOSED) ENGINE ENGINE LOAD
EVAPORATIVE CONTROL
CANISTER MODULE
VENT ENGINE SPEED

T801/1.05

AJ16 FUEL DELIVERY AND ENHANCED EVAPORATIVE EMISSION CONTROL SYSTEM

RUNNING LOSS
CONTROL VALVE
(NORMALLY OPEN)

ROLL-OVER PRESSURE FUEL

VALVE SENSOR INJ.

FUEL RAIL
INTAKE
MANIFOLD

JET CHECK
PUMP VALVE FUEL
SURGE PRESS.
POT (CHECK VALVE REG.
LOCATION VARIES
XJ6 – XJS)

FUEL TANK FUEL PUMP FUEL PUMP

1 2
(SC ONLY) FUEL FILTER

FILTER

CANISTER CLOSE
VALVE EVAPORATIVE
VALVE
(NORMALLY OPEN)
(NORMALLY CLOSED) ENGINE
EVAPORATIVE FUEL TANK PRESSURE
EVAPORATIVE CONTROL
CANISTER CANISTER MODULE ENGINE LOAD

ENGINE SPEED

T801/1.05A

10
 AJ16 4.0 Liter Engine Management System

Fuel Tank
The fuel tank has been revised to incorporate a new fuel pump (two pumps for Supercharged engines)
and the necessary plumbing for fuel supply and return. The tank uses baffle plates to reduce fuel surge
and a surge pot to ensure that a constant supply of fuel is available for the pump(s). Each pump is
located by a rubber mount and clamp attached to the surge pot. The tank interior piping incorporates
a jet pump and a check valve in the fuel return line. Returning fuel flows through the jet pump, which
draws additional cool fuel from the tank for supply to the surge pot. This supplemented return flow
ensures that the surge pot remains full of fuel. The return check valve prevents reverse flow through
the fuel return line.

Access to the tank interior is through the evaporative flange at the top of the tank.

FUEL TANK ARRANGEMENT (SEDAN RANGE)

BAFFLE PLATE
SURGE POT CHECK TANK
VALVE TWIN FUEL PUMPS

FUEL PUMP 2

FUEL PUMP 1

JET PUMP FUEL PUMP AND FILTER

T801/1.06 A & B

Fuel Pump FUEL PUMP

ELECTRICAL
CONNECTOR
A simplified fuel pump assembly is used for FUEL OUTLET
fuel delivery. The pump unit consists of a tur-
bine driven by a DC motor, a check valve and
an inlet filter. The fuel output from the turbine
pump provides a cooling flow around the
motor before being discharged through the
outlet check valve. The check valve prevents FILTER
reverse flow when the engine is switched off.

Specifications
Nominal pump delivery –
26.45 gallons per hour at 43.5 psi (3 bar)
Current draw –
PUMP MOUNTING
7 amps at 13.2V (3 bar) FUEL INLET
T801/1.07A & B

In-Line Fuel Filter

A replaceable in-line fuel filter is located in the supply line above the rear axle on the left side.

NOTES

11
AJ16 4.0 Liter Engine Management System

Fuel Delivery and Evaporative Emission Control (continued)

Fuel Pump Control: Single Fuel Pump
The electrically powered fuel pump is controlled by the ECM via the fuel pump relay. After the igni-
tion is turned on (position II), the pump runs for about 1 second to build fuel pressure for starting. When
the ECM receives an engine speed signal from the crankshaft position sensor, it activates the fuel pump
relay, which in turn switches on the fuel pump. The fuel pump will continue to run either until the ig-
nition is turned off or until approximately 1 second after there is no speed signal.

NOTE: In the event of a vehicle collision, the inertia switch will switch off all ignition powered circuits,
including the EMS power relay. This action will remove power from the ECM and cause the fuel pump
relay to de-energize, switching off the fuel pump.

SINGLE FUEL PUMP CONTROL

ENGINE CONTROL MODULE

FUEL PUMP
RELAY

ENGINE SPEED GROUND POWER

FUEL PUMP
(CRANKSHAFT POSITION SENSOR)

T801/1.08

NOTES

12
 AJ16 4.0 Liter Engine Management System

Fuel Pump Control: Twin Fuel Pumps

Supercharged engines use twin fuel pumps to ensure adequate fuel supply under high engine loads.
Fuel pump 1 operates as described for the single pump installation. Fuel pump 2 is controlled via a fuel
pump control module and operates only in the higher engine speed range. The fuel pump control
modules receives an engine speed input from the ECM and switches on fuel pump 2 at 4000 rpm and
off at 3200 rpm.

TWIN FUEL PUMP CONTROL

FUEL PUMP
ENGINE CONTROL MODULE RELAY 1

GROUND POWER
FUEL PUMP
ENGINE SPEED 1
(CRANKSHAFT
POSITION SENSOR)

ENGINE RPM GROUND

FUEL PUMP FUEL PUMP

CONTROL RELAY 2
MODULE

POWER
FUEL PUMP
2

T801/1.09

NOTES

13
AJ16 4.0 Liter Engine Management System

Fuel Delivery and Evaporative Emission Control (continued)

Fuel Rail and Pressure Regulator
Fuel is pumped to the fuel rail and injectors, where fuel pressure is controlled by the fuel pressure
regulator. The pressure regulator is a carry-over component from the AJ6 EMS. Excess fuel, above
the engine requirement, is returned to the fuel tank. The pressure regulator spring chamber above the
diaphragm is referenced to intake manifold vacuum. The differential pressure across the fuel injector
nozzles is therefore maintained constant at 44 psi (3.0 bar) and the quantity of fuel injected for a given
injector pulse duration is also constant. On normally aspirated engines, fuel pressure measured on a
test gauge will vary between 32 psi (2.3 bar) at overrun to 44 psi (3.0 bar) at full load to compensate
for intake manifold absolute pressure. On supercharged engines, the measured fuel pressure will reach
54 psi (3.66 bar) at full load.

The fuel pressure regulator is located as close as possible to the fuel rail so that good dynamic control
of fuel pressure is achieved. This design provides the same pressure across each injector, and deliv-
ers an equal quantity of fuel to each of the six cylinders.

FUEL PRESSURE REGULATOR

VACUUM (INTAKE MANIFOLD)

VACUUM (INTAKE MANIFOLD)

PRESSURE SPRING

VALVE DIAPHRAGM

FUEL SUPPLY

FUEL SUPPLY

FUEL RETURN
FUEL RETURN
T801/1.10 A & B

NOTES

14
 AJ16 4.0 Liter Engine Management System

Fuel Injectors
The fuel injectors are plate-type, twin-spray injectors as used on the 1993 / 94 model year AJ6 engine,
but with revised flow rates and coil resistance. The plate-type, twin-spray injector design has several ben-
efits: it aims a fuel spray at each intake valve throat, it is quieter in operation, and the tip is less prone to
contamination. The injectors are secured to the fuel rail with custom clips that ensure the twin jets of fuel

;;
;;;
;;
are directed to the intake valve throats. AJ16 normally aspirated injectors are identified by a white band
around the injector body; supercharged injectors are identified by a red band.

NOTE: All AJ6 and AJ16 fuel injector service replacements have green identification bands. Be sure
to verify the correct part number stamped on the injector before installation.

TWIN-SPRAY FUEL INJECTOR AND CROSS SECTION

;;;;
;;
;;;;
WHITE BAND – NORMALLY ASPIRATED

;;;;
RED BAND – SUPERCHARGED NOZZLE VALVE SEAT FILTER

;;;;
;;;;
INJECTOR COIL RESISTANCE: 16 OHMS
ARMATURE
;;;;
;;;; COIL
ASSEMBLY
SPRING

T801/1.11 A & B

The AJ16 injector drive signal is a single-width

modulated pulse. (The AJ6 injector has a large FUEL INJECTOR CHARACTERISTIC
opening pulse followed by a series of hold-on CURRENT PROFILE
pulses.)
0.75A

Fuel Injector Monitoring for OBD II

Two tests are used to check injector operation.
The first test monitors injector performance
while the engine is running. The second test
occurs at engine stall or power down to check
0A t
for an open or short circuit to the injectors. A
fault must occur on two consecutive trips
INJECTOR PULSE WIDTH
before the CHECK ENGINE MIL is activated.
Refer to Systems Readiness Test, page 53. VOLTAGE PROFILE

12v
NOTES

0v t

INJECTOR PULSE WIDTH

T801/1.12

15
AJ16 4.0 Liter Engine Management System

Fuel Delivery and Evaporative Emission Control (continued)

EVAPORATIVE EMISSION CONTROL SYSTEM (XJ6 SEDAN RANGE) Evaporative Emission Control
The fuel tank can be filled to approximately 90%
INTAKE MANIFOLD of its capacity. The additional 10% of volume
allows for expansion of the fuel without escape
to the atmosphere.

When the engine is switched off, the fuel tank

pressure is maintained at a positive pressure of
1.0 – 1.33 psi by the pressure control valve. Pres-
sure above 1.33 psi is released by the valve to
PURGE FLOW
the charcoal canister.

When the engine is running, manifold vacuum

acts on the pressure control valve, which opens
the vent line from the fuel tank to the charcoal
canister. Air enters the charcoal canister and
PRESSURE
CONTROL VALVE flows to the tank to replace the fuel delivered to
the engine and maintain atmospheric pressure in
the tank.

If the pressure control valve fails, the fuel tank cap

INTAKE MANIFOLD
VACUUM will vent the fuel tank pressure at 2.0 – 2.5 psi.
EVAPORATIVE
EVAPORATIVE CANISTER
EMISSION CONTROL
VALVE EVAPORATIVE Canister purge
FLANGE
When canister purge is enabled, the ECM
meters purge flow to the intake manifold through
the normally closed evaporative emission control
(purge) valve (EVAPP). Canister purge is enabled
by the ECM based on engine coolant tempera-
ture only when closed loop fuel metering control
is operational.

During most operating modes, the purge rate is

FUEL TANK determined from an engine speed against engine
load strategy. When the throttle is closed, the
purge rate is determined from an engine speed
T801/1.13
only strategy.

Purge Flow Monitoring for OBD II

The ECM detects purge flow in two ways: if closed loop fuel metering correction indicates a large
movement toward lean when purging is enabled, or if the idle air control valve corrects for increased
air flow when purging is enabled, the ECM has confirmation that purging is taking place. A fault must
occur on two consecutive trips before the CHECK ENGINE MIL is activated.

NOTES

16
 AJ16 4.0 Liter Engine Management System

Evaporative Emission Control Valve (EVAPP) EVAPORATIVE EMISSION CONTROL VALVE

The new evaporative emission control (purge) (XJ6 SEDAN RANGE)
valve is a normally closed design. The amount
of valve opening (and canister purge flow) is
determined by the ECM drive signal allowing
the ECM to accurately control purge flow for
the prevailing engine operating conditions.

On XJ6 Sedan Range vehicles, the new

EVAPP is mounted below the left headlight.
On XJS Range vehicles, the EVAPP is mounted
on the canister bracket.
T801/1.14

Evaporative Canister EVAPORATIVE CANISTER (XJ6 SEDAN RANGE)

The new reshaped evaporative canister (char-
coal canister) is identical in operation to previ-
ous canisters. On XJ6 Sedan Range vehicles,
the canister is located under the vehicle near
the intermediate mufflers. On XJS Range
vehicles, the canister is located in the left front
fender, behind the headlight.

T801/1.15

Air Intake System HELMHOLTZ RESONATOR

A resonance chamber has been added to the
air intake elbow on XJ6 Sedan Range vehicles
to reduce intake noise. This chamber is called
a Helmholtz resonator.

T801/1.17

NOTES

17
AJ16 4.0 Liter Engine Management System

Fuel Delivery and Evaporative Emission Control (continued)

Enhanced Evaporative Emission Control
A percentage of 1996 MY ON Sedan Range vehicles are equipped with a twin canister enhanced
evaporative emission system that provides reduced evaporative emissions and enhances the system’s
on-board diagnostic capabilities.

ENHANCED EVAPORATIVE EMISSION SYSTEM (1996 MY XJ6 SEDAN RANGE ONLY)

LD
FO
ANI
M
KE
TA
IN
TO

EVAPORATIVE CANISTERS

PRESSURE CANISTER
SENSOR CLOSE VALVE
EVAPORATIVE EMISSION
CONTROL VALVE PU FILTER
RG
EF
LO
W

RUNNING LOSS
CONTROL VALVE
T801/1.05B

The enhanced evaporative emission system consists of the following components:

• Fuel tank pressure sensor
• Running loss control valve
• Two evaporative canisters
• Canister close valve and filter
• Evaporative emission valve
• P-Cap flexible vapor lines

NOTES

18
 AJ16 4.0 Liter Engine Management System

Enhanced Evaporative Emission Control System Operation

When the engine is switched off, the normally open running loss control valve allows fuel tank vapors
through the vent line to the canisters. To maintain atmospheric pressure in the tank,
air enters the canisters through a filter via the normally open canister close valve .

When the engine is running and canister purge is enabled, the ECM meters purge flow from the can-
isters and tank via the evaporative emission control (purge) valve (EVAPP). The ECM enables canister
purge using parameters similar to the single canister system, but with different mapping.

During refueling the engine must be switched off. The incoming fuel creates a pressure differential
between the tank interior and the filler neck. The running loss control valve senses the pressure dif-
ferential and closes the vent line to the canisters.

Flexible vapor lines are constructed of P-Cap tubing to reduce vapor loss through their walls. Individual
system components connect to the vapor lines with Viton hoses and spring clamps.

NOTE: Engine compartment fuel lines are also P-Cap and include pulse dampers to prevent fuel in-
jector pulses from causing a knocking noise in the lines.

Enhanced Evaporative Emission System Diagnostic Monitoring

Purge flow monitoring – The ECM detects purge flow two ways: if closed loop fuel metering
correction indicates a large movement toward lean when purge is enabled, or if the idle air control
valve corrects for increased air flow when purging is enabled, the ECM has confirmation that purg-
ing is taking place.

NOTES

19
AJ16 4.0 Liter Engine Management System

Fuel Delivery and Evaporative Emission Control (continued)

Enhanced Evaporative Emission Control Leak monitoring
The ECM can detect system leaks as small as 1 mm (0.040 in) in diameter. The system is tested once
during every “trip” (refer to Trip and Drive Cycle page 52). The leak monitoring test cycle takes 25 to
30 seconds.

Parameters to initiate leak monitoring:

• Engine warmed to normal operating temperature from a ”cold” start
• Approximately 15 minutes elapsed since engine cranking
• Fuel level between 1/4 and 3/4 full
• Vehicle stopped with engine at idle speed after approximately one minute of steady speed
operation above 30 mph (48 km/h)

NOTE: If the engine speed is raised above idle, the test will terminate .

ENHANCED EVAPORATIVE EMISSION LEAK MONITORING Leak monitoring test sequence

The ECM ensures that the EVAPP valve is closed.
The ECM closes the normally open canister close
CANISTER EVAPP EVAPP CANISTER
CLOSE VALVE OPENS CLOSES CLOSE VALVE valve for approximately 5 seconds causing the fuel
CLOSES OPENS
FUEL TANK
tank vapor pressure to rise. (Fuel tank pressure is
PRESSURE monitored by the ECM via the pressure sensor.)
The ECM progressively opens the evaporative
emission valve and monitors fuel tank pressure
AMBIENT drop. (If the ECM detects no pressure drop, the
test is terminated.)
When fuel tank pressure drops to 2.5 kPa (0.4
-2.5 kPa psi) below the ambient pressure, the ECM closes
(0.4 psi)
the EVAPP valve and monitors the vacuum in the
TIME fuel tank for approximately five seconds.
The ECM opens the canister close valve and the
evaporative emission system returns to its nor-
T801/1.68
mal function.

If any of the following faults are detected, the ECM will flag a DTC identifying the condition:
• Vacuum leak
• Canister close valve / circuit electrical fault
• Fuel tank pressure sensor out of range
• Fuel tank pressure too low or too high

Refer to DTC Summary page 69.

NOTES

20
 AJ16 4.0 Liter Engine Management System

Running Loss Control Valve

RUNNING LOSS CONTROL VALVE
The normally open running loss control valve is FROM TANK
located on the fuel tank near the filler neck, con-
necting the fuel tank evaporative loss flange to
the carbon canisters. During refueling, the pres-
sure imbalance between the inside of the tank
and the filler neck causes the valve to close the
vent line to the canisters. This action prevents
the refueling pressure imbalance from forcing ex-
cess vapors or fuel into the canisters.

Evaporative Canister
A second canister is installed in series with the
first canister to increase vapor storage capacity.
The canister is located under the vehicle below
the right rear seat pan. The atmospheric vent for
the canisters is controlled by the canister close TO CANISTERS T801/1.69
valve and filter.

EVAPORATIVE LOSS FLANGE

Evaporative Loss Flange
ROLL-OVER VALVE TANK PRESSURE SENSOR
All Sedan Range models from the 1996 MY ON
utilize a steel evaporative loss flange. The new
roll-over valve and fuel pump electrical connec-
tors are installed in grommets in the flange.

Fuel Tank Pressure Sensor

The fuel tank pressure sensor is installed in a
grommet in the evaporative loss flange of en-
hanced evaporative emission equipped vehicles.
The sensor provides a fuel tank pressure signal to
the ECM for system diagnostics.

Canister Close Valve and Filter

The ECM controlled canister close valve and filter
assembly is installed above the right axle shaft. T801/1.67

The normally open valve is used to close the can-

ister atmospheric vent line during system
diagnostics. The non-serviceable filter prevents CANISTER CLOSE VALVE AND FILTER
contamination of the valve during canister purge.

NOTES

CANISTER
CLOSE
FILTER VALVE

T801/1.66

21
AJ16 4.0 Liter Engine Management System

Fuel Injection
Fuel metering is obtained by controlling the injector pulse duration during each engine cycle (two crank-
shaft rotations). The pulse duration is varied by the engine control module (ECM) according to several
sensor inputs. The sensed control inputs form two groups — primary and secondary. Primary control
inputs are intake mass air flow (engine load) and engine speed; secondary control inputs consist of en-
gine coolant temperature, cranking signal, throttle movement and position and exhaust oxygen content.
The injector pulse is then corrected for actual battery voltage. On normally aspirated engines, the injec-
tors are pulsed semisequentially. Semisequentially means twice per engine cycle (once per engine
revolution) in the engine firing order. On supercharged engines, the injectors are pulsed sequentially.
Sequentially means once per engine cycle (once every two engine revolutions) in the engine firing order.

Fuel metering strategies are held in memory (EPROM) in the ECM and form an engine load versus
engine speed matrix. The load and speed range of the engine is divided into 16 loads and 16 speeds
(256 memory sites). Digital numbers representing injector pulse duration in milliseconds fill each site
and cover the entire engine load and speed range. Fuel metering correction is applied for all six cylin-
ders simultaneously, not for individual cylinders.

Sequential fuel injector pulsing is ECM controlled.

FUEL INJECTION PRIMARY AND SECONDARY CONTROL
The ECM “learns” the compression stroke syn-
chronization at each engine start from the
camshaft position sensor (CMPS) and crankshaft
position sensor (CKPS) inputs. After the firing
FUEL INJECTION
ENGINE LOAD STRATEGY synchronization is learned, the ECM uses the
CKPS input for engine speed and position. Refer
ENGINE SPEED PRIMARY INJECTOR to the CMPS description on page 27 and the
PULSE DURATION
CKPS description on page 26.

CLOSED
Additional fuel injection controls are used for over-
LOOP EXHAUST OXYGEN run fuel cutoff, engine overspeed prevention and
AIR / FUEL CONTENT
RATIO fuel cutoff during wide-open-throttle cranking.

ENABLE / CANCEL
Fuel Injection Primary Control
ENGINE CRANKING
ENGINE COOLANT WARM-UP ENGINE Fuel metering is controlled primarily as a function
TEMP. COOLANT TEMP.
STRATEGY of engine load and speed. Engine load is sensed
ACCELERATION
CORRECTION
by a mass air flow sensor (MAFS) located in the
FULL LOAD FACTORS engine air intake before the throttle housing.
DECELERATION Engine speed is sensed by a crankshaft position
sensor (CKPS) located behind the front pulley.
BATTERY
The ECM processes the input from the MAFS
BATTERY
VOLTAGE
VOLTAGE and the CKPS to access pulse duration from the
CORRECTION
fuel metering strategy.

INJECTOR NOTES
PULSE DURATION

CAMSHAFT POSITION
(INITIAL INJECTORS TRIGGERED
SYNCHRONIZATION) SEMISEQUENTIALLY
(NATURALLY ASPIRATED)
OR SEQUENTIALLY
CRANKSHAFT POSITION (SUPERCHARGED)
(SYNCHRONIZATION)

T801/1.16

22
 AJ16 4.0 Liter Engine Management System

Fuel Injection Secondary Control

Secondary fuel metering control adjusts for engine coolant temperature, cranking signal, throttle move-
ment and position, exhaust oxygen content and battery voltage.

Cranking and after-start enrichment

The ECM provides fuel metering enrichment for cranking and after-start conditions by increasing the
injector pulse duration. Engine cranking is determined by an engine speed between 0 and 400 rpm.
The injector pulse duration, and the rate at which the enrichment is decreased back to the warm-
up phase, are dependent upon engine coolant temperature measured by the engine coolant
temperature sensor.

Warm-up
The programmed warm-up enrichment provides extra fuel during engine warm-up based on the
engine temperature measured by the coolant temperature sensor. The warm-up phase is applied
when the coolant temperature is between 40˚F and 160˚F (5˚C and 70˚C).

Acceleration enrichment
When the ECM senses that the throttle is opening (throttle position sensor input), the injector pulse
duration is lengthened by an amount dependent upon the rate at which the throttle is opened and on
engine coolant temperature.

Full load enrichment

If the ECM senses a full throttle input from the throttle position sensor, full load enrichment is applied
and closed loop operation is temporarily canceled.

Deceleration leaning
When the ECM senses that the throttle is closing (throttle position sensor input), the injector pulse
duration is shortened dependent on the rate at which the throttle closed, preventing a momentary
rich condition.

Battery voltage correction

Because the time to achieve full lift of the injector plate decreases as voltage increases, the amount
of fuel delivered by the injector for a given pulse duration is dependent upon the injector operating
voltage. The ECM is programmed with a voltage correction strategy. The supply voltage is monitored
by a software routine and the correction applied to the pulse duration.

Closed loop fuel metering

In order to significantly reduce exhaust emission, the exhaust system incorporates two primary and one
secondary 3-way catalytic converters that oxidize CO and HC, and reduce NOx. These converters
operate efficiently only if engine combustion is as complete as possible. A closed loop system between
fuel injection, ECM control, and exhaust oxygen content feedback is used to maintain an optimum
air / fuel ratio as close to 14.7 : 1 as possible. In response to oxygen sensor voltage swings, the ECM
continuously drives the air / fuel ratio rich-lean-rich by adding to, or subtracting from the baseline injector
pulse duration.

NOTES

23
AJ16 4.0 Liter Engine Management System

Fuel Injection (continued)

Additional Fuel Injection Controls
Overrun fuel cutoff
In order to improve fuel economy and aid in controlling exhaust emission, the ECM cancels fuel injection
during engine overrun conditions. The ECM determines overrun conditions from inputs received from
the throttle position sensor (TPS), crankshaft position sensor (CKPS) and engine coolant temperature
sensor (ECTS). Overrun fuel cutoff is enabled when the coolant temperature is above 75˚F (35˚C). Fuel
injection is cancelled when the throttle is closed and the engine speed is greater than 200 rpm.

Engine overspeed control

An engine overspeed control function limits the maximum engine speed by canceling fuel injection.
Fuel injection is cancelled when the engine speed is above 5500 rpm.

Wide-open-throttle during cranking

If the ECM senses that the throttle is wide open (throttle position sensor input) during cranking, fuel
injection is canceled to help clear a flooded engine.

NOTES

24
 AJ16 4.0 Liter Engine Management System

EMS Main Sensing Components

The inputs provided by the engine management system main sensing components are used by the
ECM to control a variety of subsystems and functions.

Engine Load MAFS LOCATION (XJ6 SEDAN RANGE)

Mass air flow sensor (MAFS)
The new mass air flow sensor (MAFS) has an
improved and simplified design with revised
calibrations for the GEMS 6 ECM.

The MAFS is a hot wire type that measures air

flow volume by the cooling effect of air pass-
ing over a heated platinum wire, altering the
electrical resistance of the wire. The electrical
resistance value is converted to an analog out-
put voltage supplied to the ECM as a measure
of air flow volume (engine load).

The heated wire sensor is located in the cen- T801/1.17

tral column that is an integral part of the cast-
ing. The column has a central tube entry and
four exit slots. A small portion of the intake air MAFS CROSS SECTION
flows through the entry tube and passes over
HEAT SINK
the heated wire sensor before returning to the AND CONTROL UNIT
main air flow through the four exit slots. The
heated sensor is an integral part of the heat
sink and control unit mounted on the main
casting. The intake screen stabilizes the air
flow through the MAFS and protects the sen-
sor from debris in the air stream.

MAFS Monitoring for OBD II

The range of the MAFS signal is checked for
values outside of the normal limits and for
open and short circuits. A fault must occur on
two consecutive trips before the CHECK
ENGINE MIL is activated. Refer to Systems
Readiness Test, page 53.

NOTES

EXIT SLOTS

HEATED
ENTRY TUBE SENSOR

T801/1.18

25
AJ16 4.0 Liter Engine Management System

EMS Main Sensing Components (continued)

CRANKSHAFT POSITION SENSOR LOCATION Engine Speed and Crankshaft Position

Crankshaft position sensor (CKPS)
The sensor portion of the crankshaft position
sensor is identical to the AJ6 sensor with a re-
vised electrical lead and bracket.

The CKPS provides the primary input to the ECM

for engine speed and engine position. The
sensor is a variable reluctance device, consisting
of a bobbin coil with a magnetic core. The steel
teeth on the crankshaft timing ring form a rotor.
T801/1.19
As the rotor teeth pass by the crankshaft position
sensor, pulses are generated.

CRANKSHAFT POSITION SENSOR

The rotor has 60 tooth positions set at 6˚ intervals
with one tooth missing. The gap identifies the
TDC position of cylinders 1 and 6. The rotor thus
provides both engine speed and crankshaft posi-
tion information to the ECM. Each tooth pulse
represents 6˚ of crankshaft rotation. Thus the
frequency of the toothed pulses are a measure of
engine speed. The sensor is mounted to the tim-
T801/1.20 ing cover on the front of the engine. The air gap
between the sensor and the rotor should be
0.020 – 0.040 in.

NOTES

26
 AJ16 4.0 Liter Engine Management System

Initial Cylinder Synchronization CAMSHAFT POSITION SENSOR

for Engine Starting
Camshaft position sensor (CMPS)
The camshaft position sensor is a Hall-effect
sensor which provides the ECM with a
sequencing input so that correct ignition and
fuel injection will begin within two-thirds of an
engine revolution at engine start. The CMPS
rotor has six “windows” of different width to
positively identify each cylinder. As a window
passes the sensor, the ECM is able to identify
the cylinder (1 through 6). T801/1.21

The CMPS is necessary because the crank-

shaft position sensor (CKPS) gap identifies CAMSHAFT POSITION SENSOR LOCATION
TDC position for both cylinders 1 and 6. With-
out the CMPS sequencing input, the ECM
would attempt engine start by trial and error,
firing each cylinder in sequence; several
engine revolutions might be required for suc-
cessful engine start. CMPS input is not required
by the ECM once the engine is running.

CMPS installation procedure

With the engine at cylinder 1 compression
TDC, the dot on the CMPS rotor should align
with the circle in the inspection window.
T801/1.22

CKPS and CMPS Monitoring for OBD II

The CKPS and CMPS are tested by cross-checking the output of the sensors. The engine will not run
with a CKPS fault. A fault must occur on two consecutive trips before the CHECK ENGINE MIL is
activated. Refer to Systems Readiness Test, page 53.

NOTES

27
AJ16 4.0 Liter Engine Management System

EMS Main Sensing Components (continued)

Engine Coolant Temperature
Engine coolant temperature sensor (ECTS)
The engine coolant temperature sensor is a negative temperature coefficient (NTC) thermistor. It is
identical to the sensor used in AJ6 engine management systems, however, the connector and leads
are revised. Engine coolant temperature is determined by the ECM by a change in resistance within
the sensor. The ECM applies 5 volts to the sensor and monitors the voltage across the pins to detect
the varying resistance.

ENGINE COOLANT TEMPERATURE SENSOR ENGINE COOLANT TEMPERATURE SENSOR LOCATION

T801/1.23 T801/1.24

Coolant temperature sensor – Coolant temperature sensor –

temperature versus resistance: temperature versus typical approx. voltage:
Coolant temperature Resistance Coolant temperature Voltage
°F °C (kilo ohms) °F °C
14 -10 9.20 14 -10 4.05
32 0 5.90 32 0 3.64
50 10 3.70 59 15 2.89
68 20 2.50 78 25 2.42
86 30 1.70 86 30 2.20
104 40 1.18 104 40 1.78
122 50 0.84 122 50 1.44
140 60 0.60 140 60 1.17
158 70 0.435 158 70 0.95
176 80 0.325 176 80 0.78
193 90 0.25 193 90 0.65
212 100 0.19 212 100 0.55

ECTS Monitoring for OBD II

Three tests are performed to check the ECTS:
1 The range of the sensor is checked for values outside the normal range.
2 A “time to warm-up” test check that the sensor responds to a rise in coolant temperature.
3 A third test checks for an abnormal fall in coolant temperature once the temperature rise is
confirmed. A fault must occur on two consecutive trips before the CHECK ENGINE MIL is activated.
Refer to Systems Readiness Test, page 53.
NOTES

28
 AJ16 4.0 Liter Engine Management System

Throttle Position
Throttle position sensor (TPS)
The throttle position sensor is a nonadjustable single-track potentiometer connected to the spindle on
the throttle shaft. The ECM adapts to the TPS idle position to compensate for aging and component
wear. The ECM applies 5 volts to the sensor and monitors the voltage across the pins to determine
throttle position: low voltage – closed throttle, high voltage – opened throttle.

THROTTLE POSITION SENSOR THROTTLE POSITION SENSOR LOCATION

T801/1.26
T801/1.25

TPS Monitoring for OBD II

The range of the TPS is checked for values outside of normal limits. A fault must occur on two consecu-
tive trips before the CHECK ENGINE MIL is activated. Refer to Systems Readiness Test, page 53.

NOTES

29
AJ16 4.0 Liter Engine Management System

EMS Main Sensing Components (continued)

OXYGEN SENSOR AND CROSS SECTION Exhaust Gas Oxygen Content

Heated oxygen sensors (HO2S)
The AJ16 EMS uses four heated oxygen sensors
that provide improved heater temperature control
and reduced warm-up time.
The heated oxygen sensors are of the Titanium
Dioxide type that have a tip composed of an alu-
mina substrate with a thick film titanium dioxide
element. This type of sensor does not require
reference air to detect the oxygen content of the
exhaust, so wetting or contamination of the sen-
sor exterior will not affect sensor performance.

The resistance of the sensor element varies

greatly with the partial presence of oxygen in the
SILICON RUBBER GLASS SEAL
exhaust gas. The change in resistance is con-
TiO2 TIP
PLUG verted to a voltage output to the ECM via a
constant voltage source and variable sensor resis-
tance. Whenever the fuel / air mixture ratio
passes 14.7:1 (Lambda = 1), the sensor delivers
a voltage swing:

Air / fuel mixture leaner than 14.7:1 –

reference voltage high (maximum 4.89 V)
SHELL COVER
T801/1.27 A & B Air / fuel mixture richer than 14.7:1 –
reference voltage low (minimum 0.015 V)

OXYGEN SENSOR CHARACTERISTIC The heater is used to bring the sensor to the
active temperature of approximately 500˚C in ap-
UPPER LEVEL proximately 20 seconds after engine start.
VOLTAGE LEAN

NOTES

LOWER LEVEL
VOLTAGE RICH

UPSTREAM DOWNSTREAM
T801/1.28

30
 AJ16 4.0 Liter Engine Management System

Four oxygen sensors are installed on the exhaust system, two upstream and two downstream of the
primary catalysts. The two downstream sensors are used by the ECM for closed loop fuel metering
correction. The upstream sensors are used for OBD catalyst monitoring. Refer to Catalytic Convert-
ers on page 48.

If the oxygen sensors are to be removed or the exhaust system replaced, the sensors and harness
connectors must be labeled to ensure that they are installed in their original locations.

Oxygen Sensor Orientation

If the sensors and connectors are not installed in their original locations, the ECM can be reprogrammed
using PDU to match the sensor locations to the ECM. This PDU routine is called Oxygen Sensor
Orientation.

CAUTION: When a new ECM or new sensors are installed or the wiring harness is changed,
the ECM must be reprogrammed using PDU.

UPSTREAM OXYGEN SENSORS DOWNSTREAM SENSORS

T801/1.29 T801/1.30

HO2S Monitoring for OBD II

Both the oxygen sensor and tip heater circuits are monitored. When the key is switched on, the sen-
sors are tested for voltage outside the normal range. The oxygen sensors are also tested when a fuel
system fault is suspected. Periodically, the sensor response rate is compared to a standard. The tip
heater circuits are checked for open and short circuits.

A fault must occur on two consecutive trips before the CHECK ENGINE MIL is activated. Refer to
Systems Readiness Test, page 53.

NOTES

31
AJ16 4.0 Liter Engine Management System

Ignition Control
Ignition Timing and Spark Distribution
Ignition timing and spark distribution are controlled by the engine control module (ECM) according to
sensor inputs. As with fuel injection, the sensed control inputs form two groups: primary and second-
ary. Primary control inputs are intake mass air flow (engine load) and engine speed; secondary control
inputs consist of engine coolant temperature, intake air temperature, throttle movement and position,
transmission upshift and knock control.

Ignition timing strategies are held in memory (EPROM) in the ECM and form an engine load versus
engine speed matrix. The load and speed range of the engine is divided into 16 loads and 16 speeds
(256 memory sites). Digital numbers representing ignition timing values fill each site. The resulting 256
ignition timing values cover the entire engine load and speed range. Ignition timing is then calculated
from the ignition timing strategy according to secondary input correction factors.

Spark distribution, in the engine firing order, is ECM controlled. The ECM “learns” the compression
stroke synchronization at each engine start from the camshaft position sensor (CMPS) input. After
starting the ECM uses the crankshaft position sensor (CKPS) input for spark timing. Refer to the CMPS
description on page 27 and the CKPS description on page 26.

NOTES

32
 AJ16 4.0 Liter Engine Management System

Ignition Primary Control IGNITION PRIMARY AND SECONDARY CONTROL

Ignition timing is controlled primarily as a func-
tion of engine load and speed. Engine load is
sensed by the mass air flow sensor (MAFS) ENGINE CONTROL MODULE

located in the engine air intake before the

throttle housing. Engine speed is sensed by a IGNITION TIMING
crankshaft position sensor (CKPS) located be- ENGINE LOAD STRATEGY
hind the engine damper. The ECM processes
the inputs from the MAFS and the CKPS and ENGINE SPEED PRIMARY
IGNITION TIMING
accesses ignition timing from the ignition tim-
ing strategy.

Six individual “on-plug” ignition coils are ENGINE CRANKING

located above each spark plug. The ECM pro- INTAKE AIR TEMP.
vides switching for each primary circuit. The THROTTLE MOVEMENT CORRECTION
FACTORS
correct firing sequence and timing of the six TRANSMISSION SHIFT
individual on-plug ignition coils is determined
A/C COMPRESSOR
by the ECM from the cylinder synchronization OPERATION
input provided by the camshaft position sen-
sor (CMPS) (initial learning at engine start) and BATTERY
VOLTAGE
the crankshaft position sensor (CKPS). Refer
to the CMPS description on page 27 and the
CKPS description on page 26. KNOCK SENSING KNOCK CONTROL

IGNITION TIMING STRATEGY

CAMSHAFT POSITION
(INITIAL
IGNITION ANGLE SYNCHRONIZATION)
IGNITION TIMING AND
SYNCHRONIZATION
CRANKSHAFT POSITION
(SYNCHRONIZATION)

IGNITION COILS

T801/1.31A
LOA D
D SPEE
INE
ENG
T801/1.31B
ON-PLUG IGNITION COILS

NOTES

T801/1.32

33
AJ16 4.0 Liter Engine Management System

Ignition Control (continued)

IGNITION COIL Ignition Coils

Each ignition coil assembly is made up of a coil
body with an integral two-pin connector plug (for
connection to the ECM), a central electrode and
an extension housing.

Ignition Coil Monitoring for OBD II

During normal running, the coil primary switching
signal is monitored for current flow and for early
activation. A fault must occur on two consecu-
tive trips before the CHECK ENGINE MIL is
activated. Refer to Systems Readiness Test,
page 53.

NOTES

T801/1.33

IGNITION COIL PRIMARY CIRCUIT CHARACTERISTIC

DWELL
CURRENT PROFILE

6A

0A t

< 2 MS

VOLTAGE PROFILE

12v
0v t

SPARK DURATION
T801/1.34

34
 AJ16 4.0 Liter Engine Management System

Ignition Secondary Control

Secondary ignition timing control inputs consist of battery voltage, engine coolant temperature, intake
air temperature, throttle movement and position, transmission upshift, and knock control.

Dwell control
The dwell angle and peak coil current are ECM controlled to maintain the required spark
energy required throughout the operating range of the engine while keeping dwell to a minimum to
avoid overheating of the ignition coils.

Engine coolant temperature correction

Ignition timing is corrected for engine coolant temperature by the ECM.

Intake air temperature correction

Ignition timing is corrected by the ECM for engine intake air temperature measured by the air tempera-
ture sensor mounted in the air inlet elbow.

Closed throttle / idle correction

Separate closed throttle idle ignition strategies for gear positions Neutral and Drive are used. Refer to Idle
Control, page 36.

Full load correction

The ECM corrects ignition timing to compensate for full load conditions.

NOTES

35
AJ16 4.0 Liter Engine Management System

Ignition Control (continued)

Ignition Secondary Control (continued)
Intake air temperature sensor (IATS)
The intake air temperature sensor (IATS) is a negative temperature coefficient (NTC) thermistor identical
to the sensor used in AJ6 engine management systems, however, the connector and leads are revised.
Intake air temperature is determined by the ECM by a change in resistance within the sensor. The ECM
applies 5 volts to the sensor and monitors the voltage across the pins to detect the varying resistance.

IATS Monitoring for OBD II

The IATS range is checked for values outside of normal limits. A fault must occur on two consecutive
trips before the CHECK ENGINE MIL is activated. Refer to Systems Readiness Test, page 53.

INTAKE AIR TEMPERATURE SENSOR LOCATION INTAKE AIR TEMPERATURE SENSOR

T801/1.35 T801/1.36

Intake air temperature sensor – Intake air temperature sensor –

temperature versus resistance: temperature versus typical approx. voltage:
Intake air temperature Resistance Intake air temperature Voltage
°F °C (kilo ohms) °F °C
14 -10 9.20 14 -10 4.05
32 0 5.90 32 0 3.64
50 10 3.70 59 15 2.89
68 20 2.50 78 25 2.42
86 30 1.70 86 30 2.20
104 40 1.18 104 40 1.78
122 50 0.84 122 50 1.44
140 60 0.60 140 60 1.17
158 70 0.435 158 70 0.95
176 80 0.325 176 80 0.78
193 90 0.25 193 90 0.65
212 100 0.19 212 100 0.55

Torque-based transmission shifting

Transmission shift quality is enhanced by “torque-based shifting”. The ECM continuously provides the
transmission control module (TCM) with a pulse width modulated (PWM) signal that represents the
engine load. This signal is generated by the ECM based on the injector pulse duration.

When a shift is to occur, the TCM calculates the necessary torque reduction and provides a PWM
“ignition retard request” signal to the ECM. The PWM torque reduction signal will vary between 20%
and 90% (20% = 0˚ ignition retard; 90% = maximum ignition retard). The actual amount of retard is
applied to the ignition advance angle after other corrections are applied.

NOTES

36
 AJ16 4.0 Liter Engine Management System

Knock control KNOCK SENSOR A LOCATION

Individual, cylinder specific ignition retard to
control knock and optimize engine power is
provided through the ECM. Two knock sen-
sors (KS) are positioned on the cylinder block
to sense engine combustion knocks. One KS
is positioned at the number 2 cylinder (for cyl-
inders 1 – 3) and one is positioned at the
number 5 cylinder (for cylinders 4 – 6). Each
knock sensor has a piezo electric sensing
element to detect broad band (2 – 20 kHz)
engine accelerations.
T801/1.37
If a knock occurs, the ECM determines which
cylinder is firing from the crankshaft position
sensor (CKPS) input, and retards the ignition KNOCK SENSOR B LOCATION
timing for that cylinder only. If, on the next
firing of that cylinder, the knock reoccurs, the
ECM will further retard the ignition timing; if
the knock does not reoccur on the next firing,
the ECM will advance the ignition timing incre-
mentally with each firing.

The knock sensing ignition retard / advance

process can continue for a particular cylinder
up to a maximum retard of 9 degrees.

KS Monitoring for OBD II

T801/1.38
Knock sensing faults are detected by using
two tests. One test checks for background
noise; the other test checks for sensor voltage KNOCK SENSOR
outside of the normal range. A fault must
occur on two consecutive trips before the
CHECK ENGINE MIL is activated. Refer to
Systems Readiness Test, page 53.

NOTES

T801/1.39

37
AJ16 4.0 Liter Engine Management System

Idle Control
Idle speed is regulated by idle air control and ignition timing.

The idle air control valve (IACV) is driven by the ECM. The ECM uses inputs received from ignition ON,
the crankshaft position sensor (CKPS), engine coolant temperature sensor (ECTS) and throttle position
sensor (TPS) as well as inputs for ignition ON / OFF, gear position, air conditioning compressor operation
and road speed to control idle.

Throttle Body and Idle Air Control Valve (IACV)

The throttle body assembly incorporates the throttle value, a fixed idle air bypass, an idle air control valve
(IACV), and a fixed single track throttle position sensor (TPS). The throttle body is heated by engine
coolant to prevent ice formation around the throttle area.

THROTTLE BODY ASSEMBLY: THROTTLE BODY ASSEMBLY :

SUPERCHARGED ENGINES NORMALLY ASPIRATED ENGINES
THROTTLE POSITION IDLE AIR
SENSOR CONTROL
VALVE

IDLE AIR
CONTROL VALVE

T801/1.41 T801/1.40

NOTES

38
 AJ16 4.0 Liter Engine Management System

The nonadjustable fixed idle air bypass provides IDLE AIR CONTROL VALVE
a base idle setting. The ECM-driven IACV pro-
vides a variable idle air bypass enabling ECM
idle air control. The nonadjustable throttle posi-
tion sensor provides the ECM with a throttle
position input. Refer to page 29. The throttle
valve will not require setting during service.

The IACV regulates a variable bypass passage.

The flow of air through the variable passage is
regulated by a stepper motor connected to a
cone-shaped valve. The stepper motor has
two coils that are pulsed by the ECM. The
pulses are phased 90˚ apart. The order in
which the coils are pulsed determines the
direction of stepper motor travel. The stepper
motor has a total travel from fully opened to T801/1.42
fully closed of approximately 230 steps.

IACV Monitoring for OBD II

IACV faults are detected by using two tests. During power down, the stepper motor coils are checked
for open and short circuits. A closed loop test monitors the idle speed control steps for values outside
normal limits without causing a change in idle speed. A fault must occur on two consecutive trips
before the CHECK ENGINE MIL is activated. Refer to Systems Readiness Test, page 53.

NOTES

39
AJ16 4.0 Liter Engine Management System

Idle Control (continued)

ECM Idle Speed Control
ECM idle speed control occurs at closed throttle when road speed is less than 3 mph. The pro-
grammed idle speed accounts for engine temperature and the loads placed on the engine by the
transmission (gear position N, D, etc.), and air conditioning compressor clutch operation.

Target stable idle speeds: Park / Neutral – 700 rpm

(normal operating temperature) Drive / R, D 2, D 3 – 580 rpm
Idle speed ± 30 rpm when coolant temperature is less than 86˚F (30˚C)
Idle speed ± 20 rpm when coolant temperature is 86˚F or higher

An ECM adaption function allows for a correction to the idle speed “base line” as the engine base idle
changes with age. The adaption values are held in nonvolatile memory (EEPROM) and will be retained
even if the battery is disconnected.
NOTE: At road speeds above 3 mph, the idle air control valve (IACV) is opened to limit overrun intake
manifold pressure. The amount that the valve is opened is based on engine speed, engine tempera-
ture and throttle opening.

Engine start-up
ECM idle speed control begins shortly after the engine is started, provided the throttle is closed (throttle
position sensor at idle) and the road speed is less than 3 mph. The stepper motor in the control valve
is closed in stages until the target idle speed is reached.

Gear position
When the gear selector is in Park or Neutral, the engine management ECM receives a ground signal
from the transmission decoder module (XJ6 Sedan Range) or rotary switch (XJS Range). The ECM
then closes the idle air control valve a predetermined number of steps in anticipation the reduced engine
load. At idle, the ECM applies ignition timing from separate closed throttle ignition strategies for gear
positions Neutral and Drive.

Air conditioning compressor clutch operation

When the air conditioning compressor clutch is energized, the ECM opens the idle air control valve a
predetermined number of steps and advances the ignition timing to adjust for the change in engine load.

Ignition switched OFF

When the ignition is switched OFF, the idle air control valve indexes to a known parked position. The
reference is from the fully closed position approximately 10 seconds after the ignition is switched OFF.

NOTES

40
 AJ16 4.0 Liter Engine Management System

Adaptive Idle Fuel Metering

Adaptive idle fuel metering is used to allow for minor engine mechanical variability and engine aging.

The ECM contains an adaptive idle fuel metering software function that automatically makes a baseline cor-
rection to the idle fuel metering strategy using long-term information from the oxygen sensors. The adaption
values are held in nonvolatile memory (EEPROM) and will be retained even if the battery is disconnected.

Adaptive Idle Fuel Metering Monitoring for OBD II

Adaptive fuel metering corrections are monitored for values outside of normal limits. There are limits
for both the fuel flow rate and air mass flow rate. A fault must occur on two consecutive trips before
the CHECK ENGINE MIL is activated. Refer to Systems Readiness Test, page 53.

NOTES

41
AJ16 4.0 Liter Engine Management System

Secondary Air Injection

Secondary air injection is employed to reduces catalyst “light off” to a minimum. “Light off” is the term
used to describe the time taken to bring the catalyst to the ideal operating temperature. After engine
start, the fuel / air mixture is initially rich. The exhaust from this rich mixture is still burning when it enters
the catalyst. Air is delivered to the exhaust system to prolong the catalyst burning time and therefore
raise the catalyst operating temperature to the ideal level as soon as possible.

Secondary air injection operates immediately after start-up for a period mapped against engine cool-
ant temperature.

When the engine coolant temperature is at or above 60˚F (16˚C), the ECM activates air injection for
15 seconds. When the coolant temperature is below 60˚F (16˚C), operation occurs up to a maximum
of 4 minutes. Air injection is cancelled at high engine speed and / or load to prevent excessive
exhaust pressure.

SECONDARY AIR INJECTION SYSTEM

AIR PUMP

CHECK AIR CLEANER

VALVE

AIR PUMP
RELAY
12V DC
ECM

T801/1.45

Secondary Air Injection Monitoring for OBD II

Secondary air injection is monitored for decreased flow. The ECM can determine the air injection flow
volume by monitoring the drift in oxygen sensor response. A fault must occur on two consecutive trips
before the CHECK ENGINE MIL is activated. Refer to Systems Readiness Test on page 53.

NOTES

42
 AJ16 4.0 Liter Engine Management System

Secondary Air Injection Pump (AIRP)

The secondary air injection pump (AIRP) is an electrically powered regenerative turbine-type pump that
is permanently lubricated and requires no periodic maintenance. The AIRP incorporates an integral
solenoid operated stop valve, which is activated to open when the pump operates to allow air flow to the
exhaust manifolds. The stop valve closes when current is switched off to prevent air flow through the
pump. The pump and stop valve are controlled by the ECM via the air injection relay.

SECONDARY AIR INJECTION PUMP: SECONDARY AIR INJECTION PUMP:

NORMALLY ASPIRATED ENGINES SUPERCHARGED ENGINES

T801/1.44 T801/1.43

NOTES

43
AJ16 4.0 Liter Engine Management System

Secondary Air Injection (continued)

Secondary Air Injection Check Valve (AIRC)
The secondary air injection check valve (AIRC),
SECONDARY AIR INJECTION CHECK VALVE
located in the delivery tube behind the air
pump, prevents the back-flow of exhaust gas
to the air pump.

SECONDARY AIR INJECTION CHECK VALVE

LOCATION

;;;;
;;;
INLET
;;;;
;;;
;;;;
;;;
; ;;
;;; T801/1.46

;;;;
;;;
NOTES

PERFORATED FLEXIBLE DISK

DISK VALVE
T801/1.47 A & B

44
 AJ16 4.0 Liter Engine Management System

Exhaust Gas Recirculation (EGR)

EGR lowers combustion temperature, which in turn aids in the reduction of NOx exhaust emission. If
the EGR valve is seized closed, uncontrolled production of NOx will result; if the valve is seized open,
the combustion temperature will lower resulting in high HC and CO exhaust emission and poor engine
performance. EGR operation is mapped against engine load and speed, throttle position, and coolant
temperature.

EGR SYSTEM
TEMPERATURE

TRANSFER PIPE VALVE POSITION INPUTS

ECM
EGR TEMPERATURE
SENSOR CONTROL
OUTPUTS

EGR VALVE

INTAKE MANIFOLD

T801/1.51

EGR Monitoring for OBD II

EGR operation is monitored by the ECM via the EGR temperature sensor. When EGR is enabled, the
ECM monitors EGR temperature and compares it with the expected temperature for a given EGR valve
opening. The valve opening is determined by feedback from the pintle position sensor (see EGR Valve
on page 46). A fault must occur on two consecutive trips before the CHECK ENGINE MIL is activated.
Refer to Systems Readiness Test, page 53.

NOTES

45
AJ16 4.0 Liter Engine Management System

Exhaust Gas Recirculation (EGR) (continued)

EGR Valve (EGRV)
The electronically operated and controlled EGR valve (EGRV) is located on the intake manifold. The
EGRV consists of three main parts: the solenoid, the pintle and seat, and the pintle position sensor.
When energized by the ECM, the solenoid pulls the pintle away from the seat to allow exhaust gas
flow into the intake manifold. Movement of the armature and pintle is resisted by three forces: the
pressure drop across the pintle and seat area, gravity, and the spring load from the pintle
position sensor.

EGR VALVE LOCATION (EARLY PRODUCTION) EGR VALVE

T801/1.48

EGR VALVE AND TEMPERATURE SENSOR (LATER PRODUCTION)

EGR TEMPERATURE
SENSOR
BREATHER ADAPTER
ASSEMBLY

EGR VALVE

T801/1.49 T801/1.50 A & B

The EGRV pintle position sensor provides feedback to the ECM for closed loop control. In addition to
closed loop EGR control, the ECM uses the EGRV position feedback to calculate fuel metering and
ignition corrections.

NOTES

46
 AJ16 4.0 Liter Engine Management System

EGR Temperature Sensor EGR VALVE INSTALLATION

(EGRT Sensor)
The EGR temperature sensor is a negative EGR TEMPERATURE EGR VALVE
SENSOR
temperature coefficient (NTC) thermistor. It is
identical to the EGR temperature sensor used ADAPTOR
in AJ6 engine management systems, how-
ever, the connector and leads are revised. The
ECM applies 5 volts to pin 1 of the sensor and
monitors the voltage across the sensor pin to
ground. The theoretical full voltage range is
from 5 to 0 volts representing maximum cold
to maximum hot.

EGR temperature sensor –

temperature versus resistance
EGR temperature Resistance
˚F ˚C (kilo ohms)
TRANSFER PIPE
122 50 600
212 100 90 INTAKE
MANIFOLD
302 150 11 T801/1.52

392 200 5
482 250 2
572 300 0.8
662 350 0.3
752 400 0.1

NOTES

47
AJ16 4.0 Liter Engine Management System

Catalytic Converters
Catalyst Monitoring for OBD II
Deterioration of catalytic conversion efficiency will create higher than acceptable HC, CO and NOx
exhaust emission.

The efficiency of the primary catalytic converters is monitored and any deterioration in efficiency is
flagged as a fault by the ECM. Monitoring for catalyst efficiency is achieved by sampling both the
incoming and outgoing exhaust at the primary catalysts. Two oxygen sensors are positioned in each
exhaust downpipe assembly — one upstream of the primary catalyst and one downstream of the
primary catalyst.

UPSTREAM OXYGEN SENSORS DOWNSTREAM OXYGEN SENSORS

T801/1.53 T801/1.54

OXYGEN SENSOR AREA DIFFERENCE By comparing the voltage swings of each set of
sensors, the ECM can detect when catalyst effi-
ciency drops off. An “area difference” technique
UPPER LEVEL
is used to compare successive oxygen sensor
VOLTAGE LEAN swing measurements.

NOTE: The CHECK ENGINE MIL will not be

activated for catalyst monitoring faults on 1995
model year vehicles, however, a DTC will be
flagged by the ECM. A fault must occur on two
consecutive trips before a DTC is flagged.
LOWER LEVEL
VOLTAGE RICH NOTES

UPSTREAM DOWNSTREAM
T801/1.55

48
 AJ16 4.0 Liter Engine Management System

Engine Misfire
Misfire Monitoring for OBD II
Engine misfire may cause catalytic converter damage and/or cause a vehicle to fail an emission inspection.

The ECM monitors the engine for misfire via the

CRANKSHAFT POSITION SENSOR
crankshaft position sensor (CKPS). The steel teeth
on the crankshaft timing ring are used as a rotor for
the sensor. The rotor has 60 tooth positions set at
6 degree intervals with one tooth missing. The
gap identifies the TDC position of cylinders 1 and
6 during one complete engine cycle (two crank-
shaft revolutions). The ECM uses the gap as a
position reference.

At each cylinder firing, the crankshaft momentarily

accelerates. The ECM records and compares the
time intervals between cylinder firings and the rotor
T801/1.56
gap to detect a misfire.

If a persistent misfire occurs, the ECM will identify the cylinder and switch off the fuel injector.

NOTE: The CHECK ENGINE MIL will not be activated for misfire monitoring faults on 1995 model year
vehicles, however, a DTC will be flagged by the ECM.

There are two levels of misfire that may be detected:

Level 1 If the misfire is not severe, the fault must occur on two consecutive trips before a DTC
is flagged.
Level 2 If the misfire is severe enough that catalyst damage may occur, the DTC is flagged
immediately.

NOTES

49
AJ16 4.0 Liter Engine Management System

Vehicle Systems Interfaces

The engine management system interfaces with the instrument pack, the air conditioning compressor clutch
circuit, and the transmission control module to provide data and sensor input, and operational control.

Instrument Pack
Vehicle road speed
The instrument pack outputs a road speed signal (pulsed signal) to the ECM. The ECM uses the sig-
nal to determine idle speed control and OBD functions.

Low fuel level

The instrument pack outputs a fuel level voltage signal to the ECM. When the voltage drops below
a specified value, fuel metering diagnostics (OBD) are canceled. Canceling the fuel metering diagnos-
tics prevents the ECM from flagging DTCs caused by the vehicle running out of fuel.

Engine speed
The ECM provides an engine speed signal (pulsed signal) to the instrument pack for operation of the
tachometer.

CHECK ENGINE MIL

If the OBD system detects a fault, the ECM outputs a warning signal (ground) to the instrument pack
for operation of the CHECK ENGINE MIL. Refer to On-Board Diagnostic Facility on pages 52 – 53.

CHECK ENGINE MIL Monitoring for OBD II

The MIL circuit is checked for open and short circuits during the instrument pack bulb check period.
A fault must occur on two consecutive key ON cycles before the ECM flags a DTC.

Climate Control / Air Conditioning

The ECM controls air conditioning compressor clutch operation from a request made by the climate
control module. When an air conditioning compressor ON request (12 volt signal) is received from the
climate control module, the ECM switches ON the compressor (via the air conditioning compressor
relay). The ECM cancels (or does not switch ON) air conditioning during a full throttle demand, and
when high engine coolant temperatures occur.

NOTES

50
 AJ16 4.0 Liter Engine Management System

Automatic Transmission
Throttle position
The ECM processes the throttle position input signal from the single track throttle position sensor (TPS)
and supplies the TCM with a pulse width modulated signal to indicate throttle position.

Gear selector position

On XJ6 Sedan Range vehicles, gear position signals are output to the ECM by the decoder module (NA)
or the linear gear position switches (SC). On XJS Range vehicles, gear position signals are output to
the ECM by the rotary switch. When the gear selector is in R, D, 2 or 3, the signal is 5 volts; when the
gear selector is in P or N, the signal is ground or 0 volts. The ECM uses the gear position inputs to
control idle speed. Refer to Ignition Control, pages 32 – 37, and Idle Control, pages 38 – 41, for a de-
tailed explanation.

Gear Selector Position Monitoring for OBD II

Gear selector position faults are detected by using two tests. One test monitors for high engine load
or gear change request signals while the gear position is P or N. The other test monitors for engine
starting when the gear position is not P or N. A fault must occur on two consecutive trips before the
CHECK ENGINE MIL is activated. Refer to Systems Readiness Test, page 53.

Engine speed and torque

The ECM supplies the TCM with engine speed and torque signals. Speed is supplied as a pulsed
voltage signal that decreases as rpm increases; torque (derived from injector pulse duration) is supplied
as a pulse width modulated (PWM) signal.

Serial Communication
Serial communication between the engine management system and PDU takes place via the serial
communication data link. Only one bidirectional serial line connects to the ECM. Serial communica-
tion is used for engine setup, accessing stored DTCs, fault diagnosis and erasing DTCs.

NOTES

51
AJ16 4.0 Liter Engine Management System

On-Board Diagnostic Facility – OBD II

The OBD facility has greatly expanded diagnostic capability, as described previously. The OBD facil-
ity continuously monitors the operation of the engine management sensors and components. In
addition the OBD facility predicts failure of subsystems by performance observation. If a fault is
detected by OBD monitoring or testing, a fault is registered and reported to the Diagnostic Status Man-
ager (DSM) (ECM internal software). The DSM decides whether to flag a DTC and activate the CHECK
ENGINE MIL. Except in cases where EMS system operation would be seriously impaired, a fault must
be detected on two consecutive trips before the CHECK ENGINE MIL is activated.

DATA LINK CONNECTOR – SEDAN RANGE DATA LINK CONNECTOR – XJS

T801/1.57 T801/1.58

If, after the MIL is activated, three sequential trips are made with no recurrence of the fault(s) and no occur-
rence of additional fault(s), the MIL will extinguish on the next trip. The fault(s) will remain stored in memory.
The DSM will erase any fault code that has not recurred in 40 consecutive engine warm-up cycles.

Faults stored in the ECM memory can only retrieved through serial communication via the data link. DTCs
are held in nonvolatile memory (EEPROM) so that disconnecting the battery does not erase stored codes.

Transmission Faults – ZF
Upon detection of a transmission fault, the TCM activates the TRANSMISSION MIL immediately. If
the same fault is detected on two consecutive trips, the TCM signals the ECM to immediately activate
the CHECK ENGINE MIL. If the transmission fault is “self corrected” by the TCM, the TRANSMISSION
MIL will extinguish at the end of the ignition cycle; however, the CHECK ENGINE MIL will remain
activated until an additional three consecutive fault-free trips have occurred.

Transmission Faults – Powertrain (Hydra-Matic)

Upon detection of a transmission fault, the TCM activates the TRANSMISSION MIL immediately, and signals
the ECM to immediately activate the CHECK ENGINE MIL. If the transmission fault is “self corrected” by
the TCM, the TRANSMISSION MIL will extinguish at the end of the ignition cycle; however, the CHECK
ENGINE MIL will remain activated until an additional three consecutive fault free trips have occurred.

Trip and Service Drive Cycle

“Trip” and “Service Drive Cycle” are terms used in conjunction with OBD II.

A “Trip” means vehicle operation, following an engine-off period, of duration and driving mode such
that all EMS components and subsystems are checked at least once by the diagnostic system, with
the exception of catalyst efficiency and evaporative system monitoring. Catalyst efficiency and evapo-
rative system monitoring require a steady vehicle speed check.

NOTES

52
 AJ16 4.0 Liter Engine Management System

To check for a reoccurrence of a DTC, a vehicle must be operated over a “Service Drive Cycle”.

A “Service Drive Cycle” is a planned routine of operating a vehicle so that the EMS components and
subsystems that are being monitored will be tested. For certain DTCs, such as that for the ECTS, the
Service Drive Cycle is simple and includes:
• ignition ON
• engine start
• engine run to normal operating temperature
• ignition OFF
For more complex diagnostic routines, such as that for EGR, additional operating modes are required.

Systems Readiness Test

It can be determined if the Service Drive Cycle was of sufficient length to test for DTC reoccurrence
by performing a PDU “Systems Readiness Test”.

The Systems Readiness Test occurs automatically when the PDU reads the DTCs from the ECM
memory and reports if a full OBD check has NOT been completed since the memory was last cleared.

OBD II Reports to Jaguar Cars

Whenever the CHECK ENGINE MIL is activated, a DTC and accompanying “freeze frame” data will
be stored in the ECM memory. This information must be retrieved using the PDU “OBD II Report”
and reported to Jaguar Cars on form S93.

Limp Home Default

In order to allow vehicle operation if a malfunction occurs, “limp home” default values are incorporated
as an ECM facility. If a sensor fault is detected by OBD, the ECM will substitute a nominal value for
the missing input(s).

Diagnostic Trouble Codes

The number of possible diagnostic trouble codes (DTCs) has been greatly increased. Each DTC is a
five place standard SAE (Society of Automotive Engineers) code that describes a subsystem and the
specific fault. Refer to the Service Manual for a complete DTC listing.

DTCs are arranged in seven major groups as follows.

PX1XX Fuel and air metering
PX2XX Fuel and air metering
PX3XX Ignition system or misfire
PX4XX Auxiliary emission controls
PX5XX Vehicle speed; idles control; auxiliary inputs
PX6XX Computer and auxiliary inputs
PX7XX Transmission control

Fault diagnostics
The Service Manual contains a Diagnostics section for OBD II specific fault finding and repair.

NOTES

53
AJ16 4.0 Liter Engine Management System

Engine Supercharger

SUPERCHARGER INSTALLATION The AJ16 supercharged engine has a throttle body

adaptor, a supercharger and a charge air cooler, to-
gether with associated ducting. These components
are installed between the throttle body and the in-
take manifold.

Air from the throttle body passes through the

throttle body adaptor to the supercharger, where
it is compressed and directed through ducts to
the charge air cooler. The charge air cooler ex-
tracts some of the heat added to the air during
compression. The compressed and cooled air
then enters the intake manifold.

A port in the supercharger outlet duct connects

with a bypass valve, which bypasses excess
CHARGE AIR COOLER compressed air back to the supercharger intake,
effectively taking the supercharger off load for a
INTAKE DUCTING
large proportion of the driving cycle.
SUPERCHARGER

T801/1.59
NOTE: 1995 model year Supercharged engines
do not have exhaust gas recirculation (EGR).

SUPERCHARGER SYSTEM
BYPASS VALVE

BYPASS VALVE
ACTUATOR

CHARGE AIR COOLER

SUPERCHARGER

ENGINE COOLANT

T801/1.60

NOTES

54
 AJ16 4.0 Liter Engine Management System

Throttle body adaptor THROTTLE BODY

The throttle body adaptor is located between BYPASS VALVE
the throttle body and the supercharger. It in-
corporates those components and connec-
tions that are on the intake manifold of nor-
mally aspirated engines. Connections for the
bypass valve and actuator are also installed.

Bypass valve
The bypass valve consists of a butterfly valve
contained in an aluminum housing installed
between the outlet duct of the supercharger
and the throttle body adaptor. A bypass valve
actuator and a spring are attached to the
spindle of the valve.

With a closed or partially open throttle, the

vacuum actuator overcomes spring pressure to
THROTTLE BODY
hold the bypass valve fully open, allowing excess ADAPTOR
air back to the supercharger intake. As the
BYPASS VALVE ACTUATOR
throttle opens, the depression in the manifold T801/1.61
decreases, and the spring progressively over-
comes the pull of the vacuum actuator to close
the valve, increasing the pressure of the air sup-
plied to the intercooler and intake manifold.

Bypass valve actuator

The bypass valve actuator is a vacuum actua-
tor attached to the spindle of the bypass valve.
The actuation pipe of the actuator connects to
the throttle body adaptor at the intake to the
supercharger.

NOTES

55
AJ16 4.0 Liter Engine Management System

Engine Supercharger (continued)

Supercharger
SUPERCHARGER
The supercharger is second generation version of
the Eaton M90, installed on the front left side of
the engine above the coolant pump. A cast
bracket attaches the supercharger to four bosses
on the cylinder block.

The belt-driven supercharger has a gearbox driv-

ing two meshed helix rotors, producing a
maximum pressure increase of approximately
0.7 bar (10.2 psi) at 2750 engine rpm. A seven-
ribbed belt, driven by the crankshaft, turns the
supercharger pulley at 2.5 times engine speed.
The supercharger is a sealed unit with an internal
lubrication system.
T801/1.62

CHARGE AIR COOLER Charge air cooler

The charge air cooler is a fin-and-tube, air-to-liquid
heat exchanger integrated into the intake mani-
fold. It cools the air leaving the supercharger to
increase the mass of air entering the engine.
Coolant flow is supplied by an electrically pow-
ered pump.

NOTES

T801/1.63

56
 AJ16 4.0 Liter Engine Management System

Intake ducting
A corrugated flexible hose connects the MAFS to a cast duct attached to the charge air cooler. The
cast duct guides the air rearwards and below the cooler. A reinforced corrugated hose connects the
downstream end of the cast air duct to the throttle body. A short length of high-temperature hose con-
nects an the supercharge outlet to an elbow on the charge air cooler intake. The joints between the
cast aluminum elbows and their respective components are sealed with O-rings.

AIR FLOW THROUGH INTAKE

INTAKE AIR BYPASS AIR

COMPRESSED AIR COMPRESSED, COOLED AIR

T801/1.64

NOTES

57
AJ16 4.0 Liter Engine Management System

Crankcase Emission Control

PART LOAD BREATHER ADAPTOR ASSEMBLY

The crankcase emission control arrangement is
similar to the 1994 AJ6 arrangement. Crankcase
vapor is collected from the camshaft cover. At
part throttle, the gases are fed into the intake
PART LOAD
BREATHER GASES manifold through a coolant heated restrictor.
During full load operation the gases are fed into
the engine through both the coolant heated
restrictor and air intake elbow connection.
ENGINE
COOLANT
The necessary crankcase vacuum is balanced by
the part throttle restrictor and the full throttle ori-
ENGINE
COOLANT fice in the inlet elbow. The restrictor and orifice
sizes have been carefully chosen to control the
crankcase vacuum while not flowing so much
gas that idle speed is affected.

The part throttle restrictor is coolant heated to

RESTRICTOR prevent icing during cold weather operation.

NOTES

CARTRIDGE ASSEMBLY

T801/1.65

58
 The following DTC section is extracted from the
DTC Summaries manual and is included here as an
aid to understanding the system.
Do not use this information to diagnose vehicle faults.

Always refer to the Model Year specific section contained in

the DTC Summaries manual for accurate information.
 DTC Summary
4.0 Liter AJ16 Engine Management System – 1995

OBD II MONITORING CONDITIONS:

When testing for DTC reoccurrence, it can be determined if the Service Drive Cycle was of sufficient length
by performing a PDU “Systems Readiness Test”.

Use the PDU “Scantool Application” disc to communicate with the EMS ECM.
The Systems Readiness Test occurs automatically when PDU establishes communication with the ECM.
PDU will report if any portion of the Systems Readiness Test has not been completed in the following format:

The following tests have been identified as incomplete:

• Module $51 (identifies EMS ECM)
Catalyst
Evaporative purge system
Secondary air system
O2 sensor
EGR system

59
60
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 59) TRIPS* POSSIBLE CAUSES
1 P0101 MAFS range / performance Drive > 1500 rpm > 4 seconds 2 TPS signal voltage high, but undetected
Blocked air filter
Blocked exhaust system
Air intake leak
MAPS to ECM sensing circuit high resistance
MAPS to ECM sensing circuit intermittent short circuit to ground
MAFS supply circuit high resistance
MAFS failure
P0102 MAFS sense circuit low voltage Engine run > 4 seconds 2 Blocked air filter
Blocked exhaust system
MAPS to ECM sensing circuit high resistance or open circuit
MAPS to ECM sensing circuit intermittent short circuit to ground
MAFS supply circuit open circuit
MAFS supply circuit short circuit to ground
MAFS failure
P0103 MAFS sense circuit high voltage Engine idle < 1000 rpm > 4 seconds 2 MAPS to ECM signal ground wire open circuit
MAPS to ECM sensing circuit short circuit to B+ voltage
MAFS failure
2 P0112 IATS sense circuit high voltage (low air temperature) Ignition ON > 4 seconds 2 IATS disconnected
IATS to ECM wiring open circuit or high resistance
IATS to ECM sensing circuit short circuit to B+ voltage
IATS internal failure
P0113 IATS sense circuit low voltage (high air temperature) Ignition ON > 4 seconds 2 IATS to ECM wiring short circuit to ground
IATS internal failure
3 P0116 ECTS range / performance Engine at normal operating temperature; drive at highway speed 2 Low coolant level
Engine thermostat stuck open
ECTS to ECM sensing circuit high resistance when hot
ECTS to ECM sensing circuit intermittent high resistance
ECTS internal failure
P0117 ECTS sense circuit high voltage (low coolant temperature) Engine run > 4 seconds 2 ECTS disconnected
ECTS to ECM sensing circuit high resistance
ECTS to ECM sensing circuit open circuit
ECTS to ECM sensing circuit short circuit to B+ voltage
ECTS internal failure
P0118 ECTS sense circuit low voltage (high coolant temperature) Engine run > 4 seconds 2 Engine overheat condition
ECTS to ECM wiring short circuit to ground
ECTS internal failure
4 P0122 TPS sense circuit low voltage Ignition ON > 1 second 2 TPS disconnected
TPS supply circuit high resistance or short circuit to ground
TPS to ECM position sense circuit open circuit or
short circuit to ground
TPS internal failure
P0123 TPS sense circuit high voltage Drive steadily < 35% load > 25 seconds 2 TPS to ECM signal ground circuit open circuit
TPS to ECM wiring (supply, sense) short circuit to each other
TPS position sense circuit short circuit to B+ voltage
MAFS signal voltage low, but undetected
TPS internal failure
3 P0125 Insufficient coolant temperature for closed loop fuel control Engine run > 7 minutes 2 Low coolant level
Engine thermostat stuck open
ECTS to ECM sensing circuit high resistance
ECTS internal failure

* Number of consecutive trips required to activate CHECK ENGINE MIL.

 GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 59) TRIPS* POSSIBLE CAUSES
5 P0131 HO2S sense circuit low voltage – Engine at normal operating temperature; idle > 25 seconds 2 HO2S sense wire short circuit to ground
cyl 1, 2, 3 (A bank), upstream (1) HO2S failure
HO2S heater malfunction (tip temperature too hot)
P0132 HO2S sense circuit high voltage – Engine at normal operating temperature; idle > 25 seconds 2 HO2S disconnected
cyl 1, 2, 3 (A bank), upstream (1) HO2S signal ground wire open circuit
HO2S sense wire open circuit
HO2S sense wire short circuit to B+ voltage
HO2S failure
HO2S heater malfunction (tip temperature too cold)
P0133 HO2S sense circuit slow response – Engine at normal operating temperature; 2 HO2S contaminated
cyl 1, 2, 3 (A bank), upstream (1) drive steadily at > 20 mph for > 25 seconds HO2S wiring harness high resistance fault
HO2S failure
P0137 HO2S sense circuit low voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0131 possible causes
cyl 1, 2, 3 (A bank), downstream (2)
P1137 HO2S sense circuit lack of “swing” – Engine at normal operating temperature; 2 Downstream HO2S harness connectors
cyl 1, 2, 3 (A bank), downstream (2) drive steadily at > 20 mph for > 25 seconds (cyl 1, 2, 3 / cyl 4, 5, 6) reversed (Perform HO2S orientation)
Sense circuit indicates lean combustion (No HO2S response) HO2S loose in exhaust pipe screw threads
HO2S sense wire open circuit
Exhaust leak before catalyst
HO2S heater malfunction (tip temperature too cold)
HO2S failure
P0138 HO2S sense circuit high voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0132 possible causes
cyl 1, 2, 3 (A bank), downstream (2)
P1138 HO2S sense circuit lack of “swing” – Engine at normal operating temperature; 2 Downstream HO2S harness connectors
cyl 1, 2, 3 (A bank), downstream (2) drive steadily at > 20 mph for > 25 seconds (cyl 1, 2, 3 / cyl 4, 5, 6) reversed (Perform HO2S orientation)
Sense circuit indicates rich combustion (No HO2S response) HO2S sense wire short circuit to ground
HO2S heater malfunction (tip temperature too hot)
HO2S failure
P0139 HO2S sense circuit slow response – Engine at normal operating temperature; 2 Refer to P0133 possible causes
cyl 1, 2, 3 (A bank), downstream (2) drive steadily at > 20 mph for > 25 seconds
P0151 HO2S sense circuit low voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0131 possible causes
cyl 4, 5, 6 (B bank), upstream (1)
P0152 HO2S sense circuit high voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0132 possible causes
cyl 4, 5, 6 (B bank), upstream (1)
P0153 HO2S sense circuit slow response – Engine at normal operating temperature; 2 Refer to P0133 possible causes
cyl 4, 5, 6 (B bank), upstream (1) drive steadily at > 20 mph for > 25 seconds
P0157 HO2S sense circuit low voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0131 possible causes
cyl 4, 5, 6 (B bank), downstream (2)
P1157 HO2S sense circuit lack of “swing” – Engine at normal operating temperature; 2 Downstream HO2S harness connectors
cyl 4, 5, 6 (B bank), downstream (2) drive steadily at > 20 mph for > 25 seconds (cyl 1, 2, 3 / cyl 4, 5, 6) reversed (Perform HO2S orientation)
Sense circuit indicates lean combustion (No HO2S response) HO2S loose in exhaust pipe screw threads
HO2S sense wire open circuit
Exhaust leak before catalyst
HO2S heater malfunction (tip temperature too cold)
HO2S failure
P0158 HO2S sense circuit high voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0132 possible causes
cyl 4, 5, 6 (B bank), downstream (2)
P1158 HO2S sense circuit lack of “swing” – Engine at normal operating temperature; 2 Downstream HO2S harness connectors
cyl 4, 5, 6 (B bank), downstream (2) drive steadily at > 20 mph for > 25 seconds (cyl 1, 2, 3 / cyl 4, 5, 6) reversed (Perform HO2S orientation)
Sense circuit indicates rich combustion (No HO2S response) HO2S sense wire short circuit to ground
HO2S heater malfunction (tip temperature too hot)
HO2S failure
P0159 HO2S sense circuit slow response – Engine at normal operating temperature; 2 Refer to P0133 possible causes
cyl 4, 5, 6 (B bank), downstream (2) drive steadily at > 20 mph for > 25 seconds

61
* Number of consecutive trips required to activate CHECK ENGINE MIL.
62
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 59) TRIPS* POSSIBLE CAUSES
6 P0171 Cylinders 1, 2, 3 (A bank) combustion too lean Engine at normal operating temperature; 2 Fuel injector blockage
drive steadily at > 20 mph for > 25 seconds Fuel injector wiring open circuit
Engine misfire
Intake manifold air leak
Exhaust air leak (before catalyst)
P1171 All cylinders combustion too lean Engine at normal operating temperature; 2 Fuel filter, system blockage
drive steadily at > 20 mph for > 25 seconds Fuel system leak
Fuel pressure regulator failure (low fuel pressure)
Low fuel pump output
Fuel injectors blocked
MAFS signal fault (low voltage)
SC engine – Incorrect MAFS installed
P0172 Cylinders 1, 2, 3 (A bank) combustion too rich Engine at normal operating temperature; 2 Exhaust air leak (before catalyst)
drive steadily at > 20 mph for > 25 seconds Fuel injector blockage
Engine misfire
P1172 All cylinders combustion too rich Engine at normal operating temperature; 2 Fuel return pipe blocked
drive steadily at > 20 mph for > 25 seconds Fuel pressure regulator failure (high fuel pressure)
Fuel injectors leaking
MAFS signal fault (high voltage)
NA engine – Incorrect MAFS installed
P0174 Cylinders 4, 5, 6 (B bank) combustion too lean Engine at normal operating temperature; 2 Refer to P0171 possible causes
drive steadily at > 20 mph for > 25 seconds
P0175 Cylinders 4, 5, 6 (B bank) combustion too rich Engine at normal operating temperature; 2 Refer to P0172 possible causes
drive steadily at > 20 mph for > 25 seconds
P1176 Adaptive fuel metering trim too lean (fuel flow rate) Engine at normal operating temperature; 2 Fuel injector supply wiring short circuit to ground
drive steadily at > 20 mph for > 25 seconds Fuel filter, system blockage
Fuel system leak
Fuel pressure regulator failure (low fuel pressure)
Low fuel pump output
Fuel injectors blocked
MAFS signal fault (low voltage)
SC engine – Incorrect MAFS installed
P1177 Adaptive fuel metering trim too rich (fuel flow rate) Engine at normal operating temperature; 2 Fuel return pipe blocked
drive steadily at > 20 mph for > 25 seconds Fuel pressure regulator failure (high fuel pressure)
Fuel injectors leaking
MAFS signal fault (high voltage)
NA engine – Incorrect MAFS installed
SC engine – Intake air leak
P1178 Adaptive fuel metering trim too lean (air flow rate) Engine at normal operating temperature; idle > 3 minutes; 2 Air intake leak
drive steadily at > 20 mph for > 3 minutes; idle > 3 minutes Low fuel pressure at idle
Blocked injector
MAFS signal fault (low voltage)
P1179 Adaptive fuel metering trim too rich (air flow rate) Engine at normal operating temperature; idle > 3 minutes; 2 High fuel pressure at idle
drive steadily at > 20 mph for > 3 minutes; idle > 3 minutes MAFS signal fault (high voltage)
NA engine – Incorrect MAFS installed

* Number of consecutive trips required to activate CHECK ENGINE MIL.

 GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 59) TRIPS* POSSIBLE CAUSES
7 P1187 HO2S heater circuit open circuit – both upstream sensors Engine idle < 1000 rpm > 3 minutes, 20 seconds 2 Both HO2S heater circuits high resistance
HO2S heater harness wiring high resistance
HO2S heater harness wiring open circuit
MAFS signal fault
Ignition fault (ignition retard causing high exhaust gas temperature)
P1188 HO2S heater circuit high resistance – both upstream sensors Engine idle > 25 seconds 2 ECM to HO2S heater wiring open circuit (or intermittent open circuit)
ECM to HO2S heater wiring short circuit to ground
Both HO2S heater circuits high resistance or open circuit
Both HO2S heaters failure
P1190 HO2S heater circuit low resistance – both upstream sensors Engine idle > 25 seconds 2 High battery voltage (>17 V) producing excess heater current
ECM to HO2S heater wiring short circuit to B+ voltage
Both HO2S heater circuits short circuit to ground
Both HO2S heaters failure
P1193 HO2S heater circuit open circuit – both downstream sensors Engine idle < 1000 rpm > 3 minutes, 20 seconds 2 Refer to P1187 possible causes
P1194 HO2S heater circuit high resistance – both downstream sensors Engine idle > 25 seconds 2 Refer to P1188 possible causes
P1196 HO2S heater circuit low resistance – both downstream sensors Engine idle > 25 seconds 2 Refer to P1190 possible causes
8 P1199 Fuel level sense circuit malfunction Start and run engine 2 Instrument pack to ECM fuel level signal circuit open circuit
Instrument pack to ECM fuel level signal circuit
short circuit to ground
Instrument pack to ECM fuel level signal circuit
short circuit to B+ voltage
Instrument pack fault (incorrect fuel level signal)
Fuel level sensor failure
9 P0201 Fuel injector circuit malfunction – cylinder 1 Engine running > 2 seconds 2 Injector disconnected
Injector harness wiring open or short circuit
Injector failure
P1201 Fuel injector circuit open or short circuit – cylinder 1 Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
P0202 Fuel injector circuit malfunction – cylinder 2 Engine running > 2 seconds 2 Refer to P0201 possible causes
P1202 Fuel injector circuit open or short circuit – cylinder 2 Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
P0203 Fuel injector circuit malfunction – cylinder 3 Engine running > 2 seconds 2 Refer to P0201 possible causes
P1203 Fuel injector circuit open or short circuit – cylinder 3 Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
P0204 Fuel injector circuit malfunction – cylinder 4 Engine running > 2 seconds 2 Refer to P0201 possible causes
P1204 Fuel injector circuit open or short circuit – cylinder 4 Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
P0205 Fuel injector circuit malfunction – cylinder 5 Engine running > 2 seconds 2 Refer to P0201 possible causes
P1205 Fuel injector circuit open or short circuit – cylinder 5 Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
P0206 Fuel injector circuit malfunction – cylinder 6 Engine running > 2 seconds 2 Refer to P0201 possible causes
P1206 Fuel injector circuit open or short circuit – cylinder 6 Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes

* Number of consecutive trips required to activate CHECK ENGINE MIL.

63
64
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 59) TRIPS* POSSIBLE CAUSES
10 P0300** Random misfire detected Run engine steady > 2 minutes 1 or 2 Fuel contaminated
Fuel injector(s) blocked or leaking
Ignition secondary circuit breakdown (coils, spark plugs)
Fuel pressure low
Cylinder compression low
Broken valve spring(s)
CKPS circuit fault (CKPS DTCs also flagged)
Fuel injector(s) circuit fault(s) (Injector DTCs also flagged)
Ignition coil primary circuit fault(s) (Ignition coil DTCs also flagged)
P0301** Misfire detected – cylinder 1 Run engine steady > 2 minutes 1 or 2 Refer to P0300 possible causes
P0302** Misfire detected – cylinder 2 Run engine steady > 2 minutes 1 or 2 Refer to P0300 possible causes
P0303** Misfire detected – cylinder 3 Run engine steady > 2 minutes 1 or 2 Refer to P0300 possible causes
P0304** Misfire detected – cylinder 4 Run engine steady > 2 minutes 1 or 2 Refer to P0300 possible causes
P0305** Misfire detected – cylinder 5 Run engine steady > 2 minutes 1 or 2 Refer to P0300 possible causes
P0306** Misfire detected – cylinder 6 Run engine steady > 2 minutes 1 or 2 Refer to P0300 possible causes
P1313 Catalyst damage misfire detected – cyl 1, 2, 3 (A bank) Run engine steady > 2 minutes 1 Refer to P0300 possible causes
P1314 Catalyst damage misfire detected – cyl 4, 5, 6 (B bank) Run engine steady > 2 minutes 1 Refer to P0300 possible causes
P1315** Persistent misfire Run engine steady > 2 minutes 1 Refer to P0300 possible causes
(one cylinder identified and injector switched off)
P1316 Misfire excess emission Run engine steady > 2 minutes 2 Refer to P0300 possible causes
11 P0327 Knock sensing circuits out of range (low voltage) Drive steadily @ 2000 rpm, 50% load > 15 seconds 2 One or both knock sensors loose in block
ECM to knock sensors wiring open circuit
ECM to knock sensors wiring short circuit to ground
ECM to knock sensors wiring high resistance
Knock sensor(s) failure
P0332 Knock sensing circuits out of range (high voltage) Drive steadily @ 2000 rpm, 50% load > 15 seconds 2 Knock sensor harness wiring shield condition (RFI interference)
Knock sensor(s) failure
12 P0335 CKPS circuit malfunction Engine idle > 10 seconds 2 CKPS mounting bracket loose
CKPS / reluctor ring alignment
CKPS to ECM sensing circuit open circuit
CKPS to ECM sensing circuit short circuit to ground
CKPS to ECM sensing circuit short circuit to B+ voltage
CKPS internal failure
P0336 CKPS range / performance Engine idle > 10 seconds 2 Foreign material on CKPS face
Reluctor ring damaged
CKPS harness wiring shield condition (RFI interference)
CKPS internal failure
P0340 CMPS circuit malfunction Engine idle > 10 seconds 2 CMPS alignment
CMPS tooth damage
CMPS harness wiring shield condition (RFI interference)
CMPS internal failure

* Number of consecutive trips required to activate CHECK ENGINE MIL.

** DTCs P1313, P1314, P1315 and P1316 will not activate the CHECK ENGINE MIL on 1995 Model Year vehicles. If DTCs P1313, P1314 or P1316 are flagged, one or more of the cylinder identification DTCs will also
be flagged (random misfire P0300 or individual cylinder P0301 – P0306). If DTC P1315 is flagged, one or more of the individual cylinder identification DTCs will also be flagged P0301 – P0306.
 GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 59) TRIPS* POSSIBLE CAUSES
13 P1361 Ignition coil primary circuit malfunction – cylinder 1 Engine running > 1 second 2 ECM to ignition coil primary circuit open circuit
ECM to ignition coil primary circuit high resistance
ECM to ignition coil primary circuit short circuit to ground
CKPS malfunction (refer to P0335, P0336)
Ignition coil failure
P1362 Ignition coil primary circuit malfunction – cylinder 2 Engine running > 1 second 2 Refer to P1361 possible causes
P1363 Ignition coil primary circuit malfunction – cylinder 3 Engine running > 1 second 2 Refer to P1361 possible causes
P1364 Ignition coil primary circuit malfunction – cylinder 4 Engine running > 1 second 2 Refer to P1361 possible causes
P1365 Ignition coil primary circuit malfunction – cylinder 5 Engine running > 1 second 2 Refer to P1361 possible causes
P1366 Ignition coil primary circuit malfunction – cylinder 6 Engine running > 1 second 2 Refer to P1361 possible causes
P1371 Ignition coil primary circuit: incorrect spark timing – cylinder 1 Engine running > 1 second 2 ECM to ignition coil primary circuit short circuit
Ignition coil failure
P1372 Ignition coil primary circuit: incorrect spark timing – cylinder 2 Engine running > 1 second 2 Refer to P1371 possible causes
P1373 Ignition coil primary circuit: incorrect spark timing – cylinder 3 Engine running > 1 second 2 Refer to P1371 possible causes
P1374 Ignition coil primary circuit: incorrect spark timing – cylinder 4 Engine running > 1 second 2 Refer to P1371 possible causes
P1375 Ignition coil primary circuit: incorrect spark timing – cylinder 5 Engine running > 1 second 2 Refer to P1371 possible causes
P1376 Ignition coil primary circuit: incorrect spark timing – cylinder 6 Engine running > 1 second 2 Refer to P1371 possible causes
14 P0400 EGR temperature sensor circuit malfunction Engine at normal operating temperature; 2 ECM to EGR temp. sensor sense wire open circuit
drive at 35% load > 5 minutes EGR temp. sensor “coked up”
EGR valve, pipework blocked (insufficient EGR flow)
EGR pipework leak (insufficient EGR flow)
EGR temp. sensor failure
P1400 EGR valve position malfunction Ignition ON > 1 second 2 EGR valve sticky, dirty or seized
ECM to EGR valve position signal wire short or open circuit
P1401 EGR position circuit out of range (low or high voltage) Ignition ON > 1 second 2 ECM to EGR valve position signal wire open circuit
ECM to EGR valve position signal wire short circuit to ground
ECM to EGR valve position signal wire short circuit to B+ voltage
EGR valve position sensor supply wire short or open circuit
EGR valve position sensor ground wire
short circuit to supply wire or open circuit
EGR valve position sensor failure (EGR valve assembly)
P1408 EGR temperature sensor circuit out of range (high voltage) Ignition ON > 1 second 2 ECM to EGR temp. sensor sense wire short circuit to ground
ECM to EGR temp. sensor sense wire short circuit to supply wire
EGR temp. sensor failure
P1409 EGR valve drive circuit malfunction Ignition ON > 1 second 2 ECM to EGR valve drive wire open circuit
ECM to EGR valve drive wire short circuit to ground
EGR valve failure

* Number of consecutive trips required to activate CHECK ENGINE MIL.

65
66
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 59) TRIPS* POSSIBLE CAUSES
15 P0411 AIR system insufficient air flow to exhaust Engine at normal operating temperature; start; idle 30 seconds 2 Sedan Range up to VIN 734672, XJS Range up to VIN 199153 –
Incorrect air pump to check valve hose.
Refer to Technical Bulletin 18-47
AIR system pipework blocked or leaking
AIR pump stuck ON or OFF
AIR pump control circuit fault
AIR pump supply circuit fault
AIR pump failure
P0413 AIR pump relay drive (coil) circuit open circuit Ignition ON > 1 second 2 Air injection relay removed
Air injection relay (coil circuit) open circuit
ECM to air injection relay (coil) wiring open circuit
ECM to air injection relay (coil) wiring short circuit to B+ voltage
P0414 AIR pump relay drive (coil) circuit short circuit Ignition ON > 1 second 2 Air injection relay (coil circuit) short circuit
ECM to air injection relay (coil) wiring short circuit to ground
16 P0420 Catalyst efficiency below threshold – cyl 1, 2, 3 (A bank) Engine at normal operating temperature; **** Exhaust leak
drive steadily > 20 mph > 1 minute, 10 seconds Upstream HO2S slow response
Upstream HO2S sense wire open or short circuit
Intake air leak
MAFS fault
P0430 Catalyst efficiency below threshold – cyl 4, 5, 6 (B bank) Engine at normal operating temperature; **** Refer to P0420 possible causes
drive steadily > 20 mph > 1 minute, 10 seconds
17 P0441 EVAP system incorrect purge flow Engine at normal operating temperature; 2 EVAP valve sticking
varied driving for 15 minutes; hot idle > 1 minute EVAP valve blocked
EVAP purge hose blocked or disconnected
EVAP canister atmosphere vent blocked
EVAP valve failure
AIR pump stuck ON
P0443 EVAP valve circuit malfunction Ignition ON > 1 second 2 EVAP valve disconnected
ECM to EVAP valve “drive” circuit open circuit
ECM to EVAP valve “drive” circuit short circuit to ground
ECM to EVAP valve “drive” circuit short circuit to B+ voltage
EVAP valve failure
18 P0500 Vehicle speed sensor malfunction (signal from instrument pack) Drive > 1900 rpm; high load > 40 seconds; 40 gear changes 2 ECM to instrument pack wiring open circuit,
short circuit or high resistance
Vehicle speed signal from instrument pack incorrect
TCM fault – requests torque reduction while vehicle stopped
ABS / TC CM vehicle speed signal incorrect
ABS wheel speed sensor fault

* Number of consecutive trips required to activate CHECK ENGINE MIL.

**** Three successive fail judgments. Diagnostic tests are performed continuously. Use PDU “Scantool” Systems Readiness Test to determine if tests are complete.
 GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 59) TRIPS* POSSIBLE CAUSES
19 P0506 Idle air control system: rpm lower than expected Engine at normal operating temperature; idle > 10 seconds 2 IACV disconnected
IACV passages blocked
IACV stepper motor jammed or mounted incorrectly
MAFS signal fault (steady high voltage)
Engine incorrect operation – open throttle / engine still idle
P0507 Idle air control system: rpm higher than expected Engine at normal operating temperature; idle > 10 seconds 2 IACV disconnected
Air leak past throttle
IACV passages blocked
IACV stepper motor jammed or mounted incorrectly
MAFS signal fault (steady low voltage)
P1508 IACV circuit open circuit Ignition ON > 15 seconds; ignition OFF 2 IACV disconnected
IACV harness wiring open circuit
IACV stepper motor failure (open circuit)
P1509 IACV circuit short circuit Ignition ON > 15 seconds; ignition OFF 2 IACV harness wiring short circuit
IACV stepper motor failure (short circuit)
20 P1514 High load NEUTRAL / DRIVE malfunction Drive at > 90% load 2 MAFS signal voltage high, but undetected
NEUTRAL / PARK wiring (decoder to ECM) short circuit to ground
BPM fault (NEUTRAL / PARK parallel circuit)
P1516 Gear change NEUTRAL / DRIVE malfunction Drive > 30 gear changes 2 NEUTRAL / PARK wiring (decoder to ECM) short circuit to ground
BPM low resistance fault (NEUTRAL / PARK parallel circuit)
TCM to ECM torque reduction request fault
Vehicle speed signal fault, but undetected
P1517 Engine cranking NEUTRAL / DRIVE malfunction Start engine 2 BPM cranking inhibit fault
BPM high resistance fault (NEUTRAL / PARK parallel circuit)
NEUTRAL / PARK wiring (decoder to ECM) open circuit
NEUTRAL / PARK wiring (decoder to ECM) short circuit to B+ voltage
22 P0605 ECM data corrupted Ignition ON 1 ECM failure
21 P1607 CHECK ENGINE MIL circuit malfunction Ignition ON 2 ECM to instrument pack / BPM wiring open circuit,
short circuit or high resistance
BPM fault (CHECK ENGINE)
Instrument pack fault (CHECK ENGINE)
23 P1775 TCM CHECK ENGINE MIL request Ignition ON 1 Possible transmission fault – check for flagged TCM DTCs
P1776 Torque reduction request signal duration fault Drive vehicle to initiate automatic gear changes 1 Driver placing rapid repeated shift demands on the transmission
requiring torque reduction – torque reduction may not be possible
Possible TCM fault (request too long)
P1777 Torque reduction circuit malfunction Engine running; normal operating temperature 2 Torque reduction signal wire open circuit
Torque reduction signal wire short circuit to ground
Torque reduction signal wire short circuit to B+ voltage
Possible TCM fault (invalid signal)

* Number of consecutive trips required to activate CHECK ENGINE MIL.

67
 DTC Summary
AJ16 Engine Management – 1996/97

OBD II MONITORING CONDITIONS:

When testing for DTC reoccurrence, it can be determined if the Service Drive Cycle was of sufficient length
by performing a PDU “Systems Readiness Test”.
Use the PDU “Scantool Application” disc to communicate with the EMS ECM.

The Systems Readiness Test occurs automatically when PDU establishes communication with the ECM.
PDU will report if any portion of the Systems Readiness Test has not been completed in the following format:
The following tests have been identified as incomplete:

• Module $51 (identifies EMS ECM)

Catalyst
Evaporative purge system
Secondary air system
O2 sensor
EGR system

69
70
PDU DATALOGGER ACRONYMS

ACLOAD Air conditioning request HO2S1HM Oxygen sensor heaters upstream

ADAPT Adaptive rate HO2S2HM Oxygen sensor heaters downstream
AMFR Adaptive air mass flow rate IAT Intake air temperature
BATT Battery voltage ISCPOS Idle air control valve (IAC)
CRANK Engine cranking signal MAFS Mass airflow sensor
DTCS Number of DTCs flagged MIL CHECK ENGINE MIL
ECT Engine coolant temperature REFIDLE Idle reference speed
EGRT Exhaust gas temperature sensor RPM Engine speed
EVP Exhaust gas recirculation valve position TCMRET Torque reduction request
FMFR Adaptive fuel mass flow rate TMS-MAFS Mass airflow
FUEL Fuel level TPS Throttle position sensor
GEAR Drive / Neutral TPS-INT Closed throttle adaptive position Intel processor
HO2S1B1 Heated oxygen sensor cyl 1 3 upstream TPS-TMS Closed throttle adaptive position TMS processor
HO2S1B2 Heated oxygen sensor cyl 4 6 upstream VSS Vehicle speed
HO2S2B1 Heated oxygen sensor cyl 1 3 downstream
HO2S2B2 Heated oxygen sensor cyl 4 6 downstream
 DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P0101 MAFS range / performance Drive > 1500 rpm > 4 seconds 2 TPS signal voltage high, but undetected
Blocked air filter
Blocked exhaust system
Air intake leak
MAPS to ECM sensing circuit high resistance
MAPS to ECM sensing circuit intermittent short circuit to ground
MAFS supply circuit high resistance
MAFS failure
P0102 MAFS sense circuit low voltage Engine run > 4 seconds 2 Blocked air filter
Blocked exhaust system
MAPS to ECM sensing circuit high resistance or open circuit
MAPS to ECM sensing circuit intermittent short circuit to ground
MAFS supply circuit open circuit or short circuit to ground
MAFS failure
P0103 MAFS sense circuit high voltage Engine idle < 1000 rpm > 4 seconds 2 MAPS to ECM signal ground wire open circuit
MAPS to ECM sensing circuit short circuit to B+ voltage
MAFS failure
P0111 IATS range / performance Engine at normal operating temperature, drive; 2 IATS disconnected
idle; drive Engine compartment hot air leak into intake tract
IATS to ECM wiring open circuit or high resistance
IATS to ECM sensing circuit short circuit to B+ voltage
IATS failure
P0112 IATS sense circuit high voltage (low air temperature) Ignition ON > 20 seconds 2 IATS disconnected
IATS to ECM wiring open circuit or high resistance
IATS to ECM sensing circuit short circuit to B+ voltage
IATS failure
P0113 IATS sense circuit low voltage (high air temperature) Ignition ON > 20 seconds 2 IATS to ECM wiring short circuit to ground
IATS failure
P0116 ECTS range / performance Engine at normal operating temperature; drive at highway speed 2 Low coolant level
Engine thermostat stuck open
ECTS to ECM sensing circuit high resistance when hot
ECTS to ECM sensing circuit intermittent high resistance
ECTS failure
P0117 ECTS sense circuit high voltage (low coolant temperature) Engine run > 4 seconds 2 ECTS disconnected
ECTS to ECM sensing circuit high resistance, open circuit or
short circuit to B+ voltage
ECTS failure
P0118 ECTS sense circuit low voltage (high coolant temperature) Engine run > 4 seconds 2 Engine overheat condition
ECTS to ECM wiring short circuit to ground
ECTS failure
P0121 TPS performance Drive at highway speed 2 Intake air or exhaust restricted
Extreme high altitude operation
Intermittent / incorrect , but undetected; TPS, engine speed,
IATS, MAFS or IACV signals
P0123 TPS sense circuit high voltage Drive steadily < 35% load > 25 seconds 2 TPS to ECM signal ground circuit open circuit
TPS to ECM wiring (supply, sense) short circuit to each other
TPS position sense circuit short circuit to B+ voltage
MAFS signal voltage low, but undetected
TPS failure

* Number of consecutive trips required to activate CHECK ENGINE MIL.

71
72
DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P0125 ECTS response Engine coolant temperature > 68º F (20º C) 2 ECTS disconnected
Run engine to coolant temperature < 68º F (20º C) < 5 seconds Low coolant level
Engine thermostat stuck open
ECTS to ECM sensing circuit high resistance, open circuit or
short circuit to B+ voltage
ECTS failure
P0131 HO2S sense circuit low voltage – Engine at normal operating temperature; idle > 25 seconds 2 HO2S sense wire short circuit to ground
cylinders 1, 2, 3 (A bank), upstream (1) HO2S failure
HO2S heater malfunction (tip temperature too hot)
P0132 HO2S sense circuit high voltage – Engine at normal operating temperature; idle > 25 seconds 2 HO2S disconnected
cylinders 1, 2, 3 (A bank), upstream (1) HO2S signal ground wire open circuit
HO2S sense wire open circuit or short circuit to B+ voltage
HO2S failure
HO2S heater malfunction (tip temperature too cold)
P0133 HO2S sense circuit slow response – Engine at normal operating temperature; 2 HO2S contaminated
cylinders 1, 2, 3 (A bank), upstream (1) drive steadily at > 20 mph (32 km/h) for > 25 seconds HO2S wiring harness high resistance fault
HO2S failure
P0137 HO2S sense circuit low voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0131 possible causes
cylinders 1, 2, 3 (A bank), downstream (2)
P0138 HO2S sense circuit high voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0132 possible causes
cylinders 1, 2, 3 (A bank), downstream (2)
P0139 HO2S sense circuit slow response – Engine at normal operating temperature; 2 Refer to P0133 possible causes
cylinders 1, 2, 3 (A bank), downstream (2) drive steadily at > 20 mph (32 km/h) for > 25 seconds
P0151 HO2S sense circuit low voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0131 possible causes
cylinders 4, 5, 6 (B bank), upstream (1)
P0152 HO2S sense circuit high voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0132 possible causes
cylinders 4, 5, 6 (B bank), upstream (1)
P0153 HO2S sense circuit slow response – Engine at normal operating temperature; 2 Refer to P0133 possible causes
cylinders 4, 5, 6 (B bank), upstream (1) drive steadily at > 20 mph (32 km/h) for > 25 seconds
P0157 HO2S sense circuit low voltage – Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0131 possible causes
cylinders 4, 5, 6 (B bank), downstream (2)
P0158 HO2S sense circuit high voltage: Engine at normal operating temperature; idle > 25 seconds 2 Refer to P0132 possible causes
cylinders 4, 5, 6 (B bank), downstream (2)
P0159 HO2S sense circuit slow response – Engine at normal operating temperature; 2 Refer to P0133 possible causes
cylinders 4, 5, 6 (B bank), downstream (2) drive steadily at > 20 mph (32 km/h) for > 25 seconds
P0171 Cylinders 1, 2, 3 (A bank) combustion too lean Engine at normal operating temperature; 2 Fuel injector blockage
drive steadily at > 20 mph (32 km/h) for > 25 seconds Fuel injector wiring open circuit
Engine misfire
Intake manifold air leak
Exhaust air leak (before catalyst)
P0172 Cylinders 1, 2, 3 (A bank) combustion too rich Engine at normal operating temperature; 2 Exhaust air leak (before catalyst)
drive steadily at > 20 mph (32 km/h) for > 25 seconds Fuel injector blockage
Engine misfire
P0174 Cylinders 4, 5, 6 (B bank) combustion too lean Engine at normal operating temperature; 2 Refer to P0171 possible causes
drive steadily at > 20 mph (32 km/h) for > 25 seconds
P0175 Cylinders 4, 5, 6 (B bank) combustion too rich Engine at normal operating temperature; 2 Refer to P0172 possible causes
drive steadily at > 20 mph (32 km/h) for > 25 seconds

* Number of consecutive trips required to activate CHECK ENGINE MIL.

 DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P0201 Fuel injector circuit malfunction – cylinder 1 Engine running > 2 seconds 2 Injector disconnected
Injector harness wiring open or short circuit
Injector failure
P0202 Fuel injector circuit malfunction – cylinder 2 Engine running > 2 seconds 2 Refer to P0201 possible causes
P0203 Fuel injector circuit malfunction – cylinder 3 Engine running > 2 seconds 2 Refer to P0201 possible causes
P0204 Fuel injector circuit malfunction – cylinder 4 Engine running > 2 seconds 2 Refer to P0201 possible causes
P0205 Fuel injector circuit malfunction – cylinder 5 Engine running > 2 seconds 2 Refer to P0201 possible causes
P0206 Fuel injector circuit malfunction – cylinder 6 Engine running > 2 seconds 2 Refer to P0201 possible causes
P0300 Random misfire detected Run engine steady > 2 minutes 2 Fuel contaminated
Fuel injector(s) blocked or leaking
Ignition secondary circuit breakdown (coils, spark plugs)
Fuel pressure low
Cylinder compression low
Broken valve spring(s)
CKPS circuit fault (CKPS DTCs also flagged)
Fuel injector(s) circuit fault(s) (Injector DTCs also flagged)
Ignition coil primary circuit fault(s) (Ignition coil DTCs also flagged)
P0301 Misfire detected – cylinder 1 Run engine steady > 2 minutes 2 Refer to P0300 possible causes
P0302 Misfire detected – cylinder 2 Run engine steady > 2 minutes 2 Refer to P0300 possible causes
P0303 Misfire detected – cylinder 3 Run engine steady > 2 minutes 2 Refer to P0300 possible causes
P0304 Misfire detected – cylinder 4 Run engine steady > 2 minutes 2 Refer to P0300 possible causes
P0305 Misfire detected – cylinder 5 Run engine steady > 2 minutes 2 Refer to P0300 possible causes
P0306 Misfire detected – cylinder 6 Run engine steady > 2 minutes 2 Refer to P0300 possible causes
P0326 Knock sensing circuit 1 (cylinders 1, 2, 3) Drive steadily @ 2000 rpm, 50% load > 15 seconds 2 Low coolant level
at maximum correction Poor quality fuel
Knock sensor harness wiring shield condition (RFI interference)
Combustion chamber deposits (pre ignition)
Mechanical or background noise
ECM failure
P0327 Knock sensing circuit 1 (cylinders 1, 2, 3) Drive steadily @ 2000 rpm, 50% load > 15 seconds 2 One or both knock sensors loose in block
out of range (low voltage) ECM to knock sensors wiring high resistance, open circuit or
short circuit to ground
Knock sensor(s) failure
P0328 Knock sensing circuit 1 (cylinders 1, 2, 3) Drive steadily @ 2000 rpm, 50% load > 15 seconds 2 Knock sensor harness wiring shield condition (RFI interference)
Knock sensor(s) failure
P0331 Knock sensing circuit 2 (cylinders 4, 5, 6) Drive steadily @ 2000 rpm, 50% load > 15 seconds 2 Low coolant level
at maximum correction Poor quality fuel
Knock sensor harness wiring shield condition (RFI interference)
Combustion chamber deposits (pre ignition)
Mechanical or background noise
ECM failure
P0332 Knock sensing circuit 2 (cylinders 4, 5, 6) Drive steadily @ 2000 rpm, 50% load > 15 seconds 2 Refer to P0327 possible causes
out of range (low voltage)
P0333 Knock sensing circuit 2 (cylinders 4, 5, 6) Drive steadily @ 2000 rpm, 50% load > 15 seconds 2 Refer to P0328 possible causes
out of range (high voltage)

* Number of consecutive trips required to activate CHECK ENGINE MIL.

73
74
DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P0335 CKPS circuit malfunction Engine idle > 10 seconds 2 CKPS mounting bracket loose
CKPS / reluctor ring alignment
CKPS to ECM sensing circuit; open circuit, short circuit to
ground or B+ voltage
CKPS failure
P0336 CKPS range / performance Engine idle > 10 seconds 2 Foreign material on CKPS face
Reluctor ring damaged
CKPS harness wiring shield condition
(RFI interference)
CKPS failure
P0340 CMPS circuit malfunction Engine idle > 10 seconds 2 CMPS alignment
CMPS tooth damage
CMPS harness wiring shield condition
(RFI interference)
CMPS failure
P0400 EGR temperature sensor circuit malfunction Engine at normal operating temperature; 2 ECM to EGR temperature sensor sense wire
drive at 35% load > 1 minutes open circuit
EGR temperature sensor “coked up”
EGR valve, pipework blocked
(insufficient EGR flow)
EGR pipework leak (insufficient EGR flow)
EGR temperature sensor failure
P0411 AIR system insufficient air flow to exhaust Engine at normal operating temperature; start; idle 30 seconds 2 AIR system pipework blocked or leaking
AIR pump stuck ON or OFF
AIR pump control circuit fault
AIR pump supply circuit fault
AIR pump failure
P0413 AIR pump relay drive (coil) circuit open circuit Ignition ON > 1 second 2 Air injection relay removed
Air injection relay (coil circuit) open circuit
ECM to air injection relay (coil) wiring open circuit or
short circuit to B+ voltage
P0414 AIR pump relay drive (coil) circuit short circuit Ignition ON > 1 second 2 Air injection relay (coil circuit) short circuit
ECM to air injection relay (coil) wiring short circuit to ground
P0420 Catalyst efficiency below threshold – Engine at normal operating temperature; *** Exhaust leak
cylinders 1, 2, 3 (A bank) drive steadily > 20 mph (32 km/h) > 1 minute, 10 seconds Upstream HO2S slow response
Upstream HO2S sense wire open or short circuit
Intake air leak
MAFS fault
P0430 Catalyst efficiency below threshold – Engine at normal operating temperature; *** Refer to P0420 possible causes
cylinders 4, 5, 6 (B bank) drive steadily > 20 mph (32 km/h) > 1 minute, 10 seconds

P0441 EVAP system incorrect purge flow Engine at normal operating temperature; 2 EVAP valve sticking
varied driving for 15 minutes; hot idle > 1 minute EVAP valve blocked
EVAP purge hose blocked or disconnected
EVAP canister atmosphere vent blocked
EVAP valve failure
AIR pump stuck ON

* Number of consecutive trips required to activate CHECK ENGINE MIL.

*** Three successive fail judgements. Diagnostic tests are performed continuously. Use the PDU “Scantool” Systems Readiness Test to determine if tests are complete.
 DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P0442 EVAP system pressure leak Engine at normal operating temperature; 2 ** Fuel tank, fuel filler cap or pipework pressure leak
(enhanced evaporative emissions vehicles) fuel level between 1/4 and 3/4 full; EVAP hoses / lines pressure leak
varied driving for > 22 minutes; EVAP valve pressure leak to engine
drive > 30 mph (48 km/h) > 10 seconds Fuel tank pressure sensor signal high
P0443 EVAP valve circuit malfunction Ignition ON > 1 second 2 EVAP valve disconnected
ECM to EVAP valve “drive” circuit; open circuit, short circuit
to ground or B+ voltage
EVAP valve failure
P0446 Canister close valve circuit malfunction Engine at normal operating temperature; 2 ECM to canister close valve open circuit, short circuit to ground
varied driving for > 22 minutes; or B+ voltage
drive > 30 mph (48 km/h) > 10 seconds Canister close valve electrical failure
P0447 Canister close valve low flow Engine at normal operating temperature; 2 ** Canister close valve blocked or stuck closed
(enhanced evaporative emissions vehicles) varied driving for 15 minutes; hot idle > 1 minute
P0452 Fuel tank pressure sensor signal low Engine run 2 ECM to fuel tank pressure sensor circuit; open circuit or
(enhanced evaporative emissions vehicles) short circuit to ground
Fuel tank pressure sensor failure
P0453 Fuel tank pressure sensor signal high Engine run 2 ECM to fuel tank pressure sensor circuit; open circuit,
(enhanced evaporative emissions vehicles) short circuit to 5V supply or B+ voltage
Fuel tank pressure sensor failure
P0460 Fuel level sense circuit malfunction Engine idle< 2 minutes 2 Instrument pack to ECM fuel level signal circuit; open circuit,
short circuit to ground or B+ voltage
Instrument pack fault (incorrect fuel level signal)
Fuel level sensor failure
P0461 Fuel level sense signal performance Drive > 10 mph (16 km/h) > 50 minutes 2 Instrument pack to ECM fuel level signal circuit; open circuit,
short circuit to ground or B+ voltage
Instrument pack fault (incorrect fuel level signal)
Fuel level sensor failure
P0500 Vehicle speed sensor malfunction Drive > 1900 rpm; high load > 40 seconds; 40 gear changes 2 ECM to instrument pack wiring: open circuit, short circuit or
(signal from instrument pack) high resistance
Vehicle speed signal from instrument pack incorrect
TCM fault – requests torque reduction while vehicle stopped
ABS / TC CM vehicle speed signal incorrect
ABS wheel speed sensor fault
P0506 Idle air control system: rpm lower than expected Engine at normal operating temperature; idle > 10 seconds 2 IACV disconnected
IACV passages blocked
IACV stepper motor jammed or mounted incorrectly
MAFS signal fault (steady high voltage)
Engine incorrect operation – open throttle / engine still idle
P0507 Idle air control system: rpm higher than expected Engine at normal operating temperature; idle > 10 seconds 2 IACV disconnected
IACV passages blocked
IACV stepper motor jammed or mounted incorrectly
MAFS signal fault (steady low voltage)
P0508 IACV circuit: open circuit Run engine; switch ignition OFF 2 IACV circuit open circuit
IACV malfunction
P0509 IACV circuit: short circuit Run engine; switch ignition OFF 2 IACV circuit short circuit to ground or B+ voltage
IACV malfunction
P0605 ECM data corrupted Ignition ON 1 ECM failure

* Number of consecutive trips required to activate CHECK ENGINE MIL.

** Through 1996 MY: DTC does not activate the CHECK ENGINE MIL.

75
76
DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES

P1137 HO2S sense circuit lack of “swing” – Engine at normal operating temperature; 2 Downstream HO2S harness connectors (cylinders 1, 2, 3 /
cylinders 1, 2, 3 (A bank), downstream (2) drive steadily at > 20 mph (32 km/h) for > 30 seconds cylinders 4, 5, 6) reversed (Perform HO2S orientation)
Sense circuit indicates lean combustion (No HO2S response) HO2S loose in exhaust pipe screw threads
HO2S sense wire open circuit
Exhaust leak before catalyst
HO2S heater malfunction (tip temperature too cold)
HO2S failure
P1138 HO2S sense circuit lack of “swing” – Engine at normal operating temperature; 2 Downstream HO2S harness connectors (cylinders 1, 2, 3 /
cylinders 1, 2, 3 (A bank), downstream (2) drive steadily at > 20 mph (32 km/h) for > 30 seconds cylinders 4, 5, 6) reversed (Perform HO2S orientation)
Sense circuit indicates lean combustion (No HO2S response) HO2S sense wire short circuit to ground
HO2S heater malfunction (tip temperature too hot)
HO2S failure
P1157 HO2S sense circuit lack of “swing” – Engine at normal operating temperature; 2 Refer to P1137 possible causes
cylinders 4, 5, 6 (B bank), downstream (2) drive steadily at > 20 mph (32 km/h) for > 30 seconds
Sense circuit indicates lean combustion
(No HO2S response)
P1158 HO2S sense circuit lack of “swing” – Engine at normal operating temperature; 2 Refer to P1138 possible causes
cylinders 4, 5, 6 (B bank), downstream (2) drive steadily at > 20 mph (32 km/h) for > 30 seconds
Sense circuit indicates rich combustion
(No HO2S response)
P1171 All cylinders combustion too lean Engine at normal operating temperature; 2 Fuel filter, system blockage
drive steadily at > 20 mph (32 km/h) for > 25 seconds Fuel system leak
Fuel pressure regulator failure (low fuel pressure)
Low fuel pump output
Fuel injectors blocked
MAFS signal fault (low voltage)
SC engine – Incorrect MAFS installed
P1172 All cylinders combustion too rich Engine at normal operating temperature; 2 Fuel return pipe blocked
drive steadily at > 20 mph (32 km/h) for > 25 seconds Fuel pressure regulator failure (high fuel pressure)
Fuel injectors leaking
MAFS signal fault (high voltage)
NA engine – Incorrect MAFS installed
P1176 Adaptive fuel metering trim too lean Engine at normal operating temperature; 2 Fuel injector supply wiring short circuit to ground
(fuel flow rate) drive steadily at > 20 (32 km/h) mph for > 25 seconds Fuel filter, system blockage
Fuel system leak
Fuel pressure regulator failure (low fuel pressure)
Low fuel pump output
Fuel injectors blocked
MAFS signal fault (low voltage)
SC engine – Incorrect MAFS installed
P1177 Adaptive fuel metering trim too rich Engine at normal operating temperature; 2 Fuel return pipe blocked
(fuel flow rate) drive steadily at > 20 mph (32 km/h) for > 25 seconds Fuel pressure regulator failure (high fuel pressure)
Fuel injectors leaking
MAFS signal fault (high voltage)
NA engine – Incorrect MAFS installed
SC engine – Intake air leak
P1178 Adaptive fuel metering trim too lean Engine at normal operating temperature; 2 Air intake leak
(air flow rate) idle > 3 minutes; drive steadily at > 20 mph (32 km/h) Low fuel pressure at idle
for > 3 minutes; idle > 3 minutes Blocked injector
MAFS signal fault (low voltage)

* Number of consecutive trips required to activate CHECK ENGINE MIL.

 DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P1179 Adaptive fuel metering trim too rich Engine at normal operating temperature; 2 High fuel pressure at idle
(air flow rate) idle > 3 minutes; drive steadily at > 20 mph (32 km/h) MAFS signal fault (high voltage)
for > 3 minutes; idle > 3 minutes NA engine – Incorrect MAFS installed
P1185 HO2S heater circuit open circuit – Engine idle < 1000 rpm > 3 minutes, 20 seconds 2 HO2S heater circuits high resistance
both upstream sensors HO2S heater harness wiring high resistance,
open circuit or short circuit to ground
P1186 HO2S heater circuit short circuit – Engine idle < 1000 rpm > 3 minutes, 20 seconds 2 HO2S heater circuits short circuit to sensor
both upstream sensors HO2S heater harness wiring short circuit to B+ voltage
P1187 HO2S heater circuit open circuit – Engine idle < 1000 rpm > 3 minutes, 20 seconds 2 HO2S heater circuits high resistance
both upstream sensors HO2S heater harness wiring high resistance
HO2S heater harness wiring open circuit
MAFS signal fault
Ignition fault (ignition retard causing high
exhaust gas temperature)
P1188 HO2S heater circuit high resistance – Engine idle > 25 seconds 2 ECM to HO2S heater wiring open circuit
both upstream sensors (or intermittent open circuit)
ECM to HO2S heater wiring short circuit to ground
HO2S heater circuits high resistance or open circuit
HO2S heaters failure
P1189 HO2S heater circuit low resistance – Engine idle > 25 seconds 2 HO2S loose
both upstream sensors HO2S heater circuit; short circuit to ground or B+ voltage
HO2S heater circuits; high resistance or open circuit
HO2S heaters failure
P1190 HO2S heater circuit low resistance – Engine idle > 25 seconds 2 High battery voltage (>17v) producing excess heater current
both upstream sensors ECM to HO2S heater wiring; short circuit to B+ voltage
HO2S heater circuits; short circuit to ground
Both HO2S heaters failure
P1191 HO2S heater circuit open circuit – Engine idle < 1000 rpm > 3 minutes, 20 seconds 2 Refer to P1185 possible causes
both downstream sensors
P1192 HO2S heater circuit short circuit – Engine idle < 1000 rpm > 3 minutes, 20 seconds 2 Refer to P1186 possible causes
both downstream sensors
P1193 HO2S heater circuit open circuit – Engine idle < 1000 rpm > 3 minutes, 20 seconds 2 Refer to P1187 possible causes
both downstream sensors
P1194 HO2S heater circuit high resistance – Engine idle > 25 seconds 2 Refer to P1188 possible causes
both downstream sensors
P1195 HO2S heater circuit low resistance – Engine idle > 25 seconds 2 Refer to P1189 possible causes
both downstream sensors
P1196 HO2S heater circuit low resistance – Engine idle > 25 seconds 2 Refer to P1190 possible causes
both downstream sensors
P1201 Fuel injector circuit open or short circuit – Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
cylinder 1
P1202 Fuel injector circuit open or short circuit – Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
cylinder 2
P1203 Fuel injector circuit open or short circuit – Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
cylinder 3
P1204 Fuel injector circuit open or short circuit – Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
cylinder 4

* Number of consecutive trips required to activate CHECK ENGINE MIL.

77
78
DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P1205 Fuel injector circuit open or short circuit – Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
cylinder 5
P1206 Fuel injector circuit open or short circuit – Run engine; ignition OFF > 2 seconds 2 Refer to P0201 possible causes
cylinder 6
P1313 Catalyst damage misfire detected – Run engine steady > 2 minutes 1 ** Refer to P0300 possible causes
cylinders 1, 2, 3 (A bank)
P1314 Catalyst damage misfire detected – Run engine steady > 2 minutes 1 ** Refer to P0300 possible causes
cylinders 4, 5, 6 (B bank)
P1315 Persistent misfire (one cylinder Run engine steady > 2 minutes 1 Refer to P0300 possible causes
identified and injector switched off)
P1316 Misfire excess emission Run engine steady > 2 minutes 2 ** Refer to P0300 possible causes
P1361 Ignition coil primary circuit malfunction – Engine running > 1 second 2 ECM to ignition coil primary circuit high resistance, open circuit
cylinder 1 or short circuit to ground
CKPS malfunction (refer to P0335, P0336)
Ignition coil failure
P1362 Ignition coil primary circuit malfunction – Engine running > 1 second 2 Refer to P1361 possible causes
cylinder 2
P1363 Ignition coil primary circuit malfunction – Engine running > 1 second 2 Refer to P1361 possible causes
cylinder 3
P1364 Ignition coil primary circuit malfunction – Engine running > 1 second 2 Refer to P1361 possible causes
cylinder 4
P1365 Ignition coil primary circuit malfunction – Engine running > 1 second 2 Refer to P1361 possible causes
cylinder 5
P1366 Ignition coil primary circuit malfunction – Engine running > 1 second 2 Refer to P1361 possible causes
cylinder 6
P1371 Ignition coil primary circuit: Engine running > 1 second 2 ECM to ignition coil primary circuit short circuit
incorrect spark timing – cylinder 1 Ignition coil failure
P1372 Ignition coil primary circuit: Engine running > 1 second 2 Refer to P1371 possible causes
incorrect spark timing – cylinder 2
P1373 Ignition coil primary circuit: Engine running > 1 second 2 Refer to P1371 possible causes
incorrect spark timing – cylinder 3
P1374 Ignition coil primary circuit: Engine running > 1 second 2 Refer to P1371 possible causes
incorrect spark timing – cylinder 4
P1375 Ignition coil primary circuit: Engine running > 1 second 2 Refer to P1371 possible causes
incorrect spark timing – cylinder 5
P1376 Ignition coil primary circuit: Engine running > 1 second 2 Refer to P1371 possible causes
incorrect spark timing – cylinder 6
P1400 EGR valve position malfunction Ignition ON > 1 second 2 EGR valve sticky, dirty or seized
ECM to EGR valve position signal wire short or open circuit
P1401 EGR position circuit out of range Ignition ON > 1 second 2 ECM to EGR valve position signal wire open circuit, short circuit
(low or high voltage) to ground or B+ voltage
EGR valve position sensor supply wire short or open circuit
EGR valve position sensor ground wire short circuit to supply
wire or open circuit
EGR valve position sensor failure (EGR valve assembly)

* Number of consecutive trips required to activate CHECK ENGINE MIL.

** Through 1996 MY: DTC does not activate CHECK ENGINE MIL. If DTCs P1313, P1314 or P1316 are flagged, one or more of the cylinder identification DTCs will also be flagged (random misfire P0300 or
individual cylinder P0301 – P0306). If DTC P1315 is flagged, one or more of the individual cylinder identification DTCs (P0301 – P0306) will also be flagged.
 DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P1408 EGR temperature sensor circuit out of range Ignition ON > 1 second 2 ECM to EGR temperature sensor sense wire
(high voltage) short circuit to ground
ECM to EGR temperature sensor sense wire short circuit
to supply wire
EGR temperature sensor failure
P1409 EGR valve drive circuit malfunction Ignition ON > 1 second 2 ECM to EGR valve drive wire open circuit
ECM to EGR valve drive wire short circuit to ground
EGR valve failure
P1440 EVAP valve incorrect flow Engine at normal operating temperature; 2 EVAP valve stuck open
(enhanced evaporative emissions vehicles) fuel level between 1/4 and 3/4 full; Fuel tank pressure sensor low output (but in range)
varied driving for > 22 minutes; Fuel tank filled with engine running
drive > 30 mph (48 km/h) > 10 seconds
P1448 Enhanced evaporative emissions Engine at normal operating temperature; 2 ** Fuel tank, fuel filler cap or pipework pressure leak
system performance fault 2 fuel level between 1/4 and 3/4 full; EVAP hoses / lines pressure leak
(vacuum test OK but no feedback change) varied driving for > 22 minutes; EVAP valve leaking pressure to engine
drive > 30 mph (48 km/h) > 10 seconds Canister close valve stuck open

P1496 Enhanced evaporative emissions Engine at normal operating temperature; 2 ** Fuel tank filled with engine running
system performance fault 1 fuel level between 1/4 and 3/4 full; Fuel tank, fuel filler cap or pipework pressure leak
(vacuum test OK but no feedback change) varied driving for > 22 minutes; EVAP hoses / lines pressure leak
drive > 30 mph (48 km/h) > 10 seconds EVAP valve stuck closed

Canister close valve stuck open

Fuel tank pressure sensor signal circuit resistance
Fuel tank pressure sensor malfunction
P1508 IACV circuit open circuit Ignition ON > 15 seconds; ignition OFF 2 IACV disconnected
IACV harness wiring open circuit
IACV stepper motor failure (open circuit)
P1509 IACV circuit short circuit Ignition ON > 15 seconds; ignition OFF 2 IACV harness wiring short circuit
IACV stepper motor failure (short circuit)
P1514 High load NEUTRAL / DRIVE malfunction Drive at > 90% load 2 MAFS signal voltage high, but undetected
NEUTRAL / PARK wiring (decoder to ECM)
short circuit to ground
BPM fault (NEUTRAL / PARK parallel circuit)
P1516 Gear change NEUTRAL / DRIVE malfunction Drive > 30 gear changes 2 NEUTRAL / PARK wiring (decoder to ECM)
short circuit to ground
BPM low resistance fault (NEUTRAL / PARK parallel circuit)
TCM to ECM torque reduction request fault
Vehicle speed signal fault, but undetected
P1517 Engine cranking NEUTRAL / DRIVE malfunction Start engine 2 BPM cranking inhibit fault
BPM high resistance fault (NEUTRAL / PARK parallel circuit)
NEUTRAL / PARK wiring (decoder to ECM) open circuit or
short circuit to B+ voltage
P1607 CHECK ENGINE MIL circuit malfunction Ignition ON 2 ECM to instrument pack / BPM wiring open circuit, short circuit
or high resistance
BPM fault (CHECK ENGINE)
Instrument pack fault (CHECK ENGINE)
P1775 TCM CHECK ENGINE MIL request Ignition ON 1 Possible transmission fault – check for flagged TCM DTCs

* Number of consecutive trips required to activate CHECK ENGINE MIL.

** Through 1996 MY: DTC does not activate the CHECK ENGINE MIL.

79
80
DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 69) TRIPS* POSSIBLE CAUSES
P1776 Torque reduction request signal duration fault Drive vehicle to initiate automatic gear changes 1 Driver placing rapid repeated shift demands on the transmission
requiring torque reduction – torque reduction may
not be possible
Possible TCM fault (request too long)
P1777 Torque reduction circuit malfunction Engine running; normal operating temperature 2 Torque reduction signal wire open circuit, short circuit to
ground or B+ voltage
Possible TCM fault (invalid signal)
P1794 ECM B+ supply voltage low (below 10.5 V) Run engine > 1600 rpm 2 Generator drive belt loose
ECM B+ supply circuit; high resistance, open circuit or
short circuit to ground
Battery malfunction
Charging system malfunction

* Number of consecutive trips required to activate CHECK ENGINE MIL.

The following Figures and Data pages are extracted from select
Electrical Guides and are included here as an
aid to understanding the Engine Management system.
Do not use this information to diagnose vehicle faults.

Always refer to the Model and Model Year specific

Electrical Guide for accurate information.
 AJ6 4.0L Engine Management System

Contents

System Description
Overview 4–5
Engine Control Module (ECM) 6
Crankcase Emission Control 7
Fuel Delivery and Evaporative Emission Control 8 – 17
Fuel Injection; Idle Speed Control 18 – 27
Ignition Timing Control 28 – 29
Air Injection 30
Exhaust Gas Recirculation 31 – 32
On-Board Diagnostics 33 – 34
Vehicle Systems Interfaces 35
Serial Communication 35

Component Location
EMS Components Installed on Engine 36
EMS Components Installed on Vehicle 37

Component Description
Fuel Pump 38
Fuel Pump Module 39
Fuel Pressure Regulator 40
Purge Valve 41
Fuel Injectors 42 – 43
Mass Air Flow Sensor 44
Crankshaft Sensor 45
Throttle Position Sensor 46
Coolant Temperature Sensor 47
Intake Air Temperature Sensor 48
Oxygen Sensor 49
Idle Speed Control Valve 50 – 51
Air Injection Pump 52
Air Switching Valve 52
Air Injection Check Valve 53
Air Injection Solenoid Vacuum Valve 53
EGR Valve 54
EGR Solenoid Vacuum Valve 55
EGR Temperature Sensor 55
Ignition Module 56
Ignition Distributor 56

1
System Description AJ6 4.0L Engine Management System

The AJ6 4.0 Litre Engine Management System (EMS) is used in 1990 – 1994 model year Sedan
Range vehicles and 1993 – 1994 model year XJS Range vehicles. This system combines the con-
trol of all engine operating and emission related components through a single microprocessor
based Engine Control Module (ECM). The ECM incorporates an On-Board Diagnostics (OBD) sys-
tem that monitors certain ECM control and drive functions for faults. The OBD system is known
as “OBD level one specification”. OBD I is the common abbreviation.

AJ6 4.0 LITRE ENGINE

T800/F.01

3
AJ6 4.0L Engine Management System System Description

Overview
The AJ6 4.0 Litre Engine Management System (EMS) is an integrated engine management sys-
tem, controlled through a digital Electronic Control Module (ECM) containing a microprocessor.
The system maintains optimum performance over the engine operating range by precisely con-
trolling fuel injection, ignition timing and emission control functions. In addition, the ECM provides
various interface outputs and incorporates an on-board diagnostic function.

A summary of EMS function and control includes:

• Fuel delivery (fuel pump)
• Evaporative emission control (canister purge)
• Fuel injection
• Cold start
• Warm-up
• Exhaust emission
• Oxygen sensor feedback
• Overrun fuel cut-off
• RPM limitation (engine overspeed)
• Wide-open-throttle fuel cut-off
• Ignition timing
• Idle speed control
• Air injection
• Exhaust gas recirculation
• Adaptive idle fuel metering (1993 MY ON)
• On-Board Diagnostics (OBD)
• “Limp home” capability
• Vehicle systems interfaces
• Serial communication (ISO)

4
 FUEL PUMP RELAY

FUEL
PUMP
ECM ECM
FUEL TANK PRESSURE
FILTER REGULATOR

FUEL RAIL
IDLE SPEED
CONTROL VALVE
System Description

ECM MASS AIR FLOW

ECM DIST. SENSOR
O 2 SENSOR INJECTOR

AIR INJ. EGR

PUMP THROTTLE
TEMP. POS. SENSOR
SPARK SENS. AIR TEMP.
EGR PLUGS EGR SENSOR
VALVE
TYPICAL AJ6 4.0 LITRE ENGINE MANAGEMENT SYSTEM

CONTROL ECM
VALVE
ECM
ECM
ECM
COOLANT ECM AIR INJ. FUEL
TEMPERATURE EGR PUMP PUMP
SENSOR SOLENOID
DIST.
VACUUM
VALVE
AIR FUEL
PUMP PUMP MAIN
ECM RELAY RELAY RELAY
IGNITION
CRANKSHAFT
SENSOR
ECM

COIL
IGN. “ON” IGN. MODULE
RELAY SENSORS

INJECTORS
A.C. CLUTCH
IGNITION

IDLE SPEED SERIAL COMMUNICATIONS

EGR
VEHICLE SYSTEMS INTERFACE
CANISTER PURGE
VCM / INSTRUMENT PACK
OBD MONITORING

ENGINE CONTROL MODULE

T800/1.01

5
AJ6 4.0L Engine Management System
AJ6 4.0L Engine Management System System Description

Engine Control Module (ECM)

The AJ6 4.0L EMS is microprocessor based using the Lucas 15 CU ECM as the heart of the
system. The 15 CU ECM microprocessor runs at 2.0 MHz. The ECM uses discrete components
plus analog-to-digital circuits to interface between the microprocessor and the input sensors and
output devices. Software, programmed into an EPROM, is divided into “control code” and
“data” (engine calibration). Control code is common to all engine specifications; data is written
for specific market specifications such as US EPA emission regulations.

15 CU ENGINE CONTROL MODULE

YELLOW

BLUE

T800/1.18

The ECM contains two double sided printed circuit boards. One is a low power board and the
other is a high power board. The yellow and blue 25-way connectors are therefore referred to
as the low and high power connectors respectively. Most of the input signals from engine
mounted sensors, and interfaces with other systems are located on the low power (Yellow)
connector. The high power connector (Blue), mainly serves outputs such as fuel injector drive
and relay activation.

The ECM receives sensor inputs and feedbacks, which are used to determine the optimum strat-
egy for the prevailing conditions. The ECM’s strategy has 256 memory locations containing
injector pulse durations and ignition timing angles for 16 different engine loads (engine load sites)
and 16 different engine speeds (engine speed sites). Canister purge, idle speed, air injection and
exhaust gas recirculation are controlled by the ECM from stored strategies.

6
System Description AJ6 4.0L Engine Management System

Crankcase Emission Control

In order to prevent crankcase vapor from escaping to the atmosphere, a closed crankcase emis-
sion control system is employed that maintains a slight vacuum in the crankcase under all engine
operating conditions.

Crankcase vapor is collected from the camshaft

CRANKCASE EMISSION CONTROL
cover and from the oil filler tube. At part
throttle, the gases are fed into the intake mani-
fold through a coolant heated restrictor. During
full load operation the gases are fed into the HEATING ELEMENT
engine through both the coolant heated
restrictor and air intake elbow connection.

The necessary crankcase vacuum is balanced

by the part throttle restrictor and the full
throttle orifice in the inlet elbow. The restrictor
and orifice sizes have been carefully chosen to
control the crankcase vacuum while not flow-
ing so much gas that idle speed is affected.

The part throttle restrictor is coolant heated to CONTROL ORIFICE

INTAKE ELBOW

prevent icing during cold weather operation. An

additional electrical breather heater element is BLOW-BY
COOLANT
located in the full throttle breather hose. The
electrical heater provides heat to the gases
passing through the hose, preventing ice forma-
INTAKE MANIFOLD
tion in the inlet elbow orifice. The electrical
heater element is controlled independently of
PART LOAD RESTRICTOR: 2.5mm; FULL LOAD ORIFICE: 8.0mm T800/1.02
the EMS ECM by an ambient temperature sen-
sor, thermal switch and relay. Starting in the
1994 model year, a throttle housing heated by
engine coolant was introduced.

7
AJ6 4.0L Engine Management System System Description

Fuel Delivery and Evaporative Emission Control

Since the 1990 model year, two fuel delivery and evaporative emission control systems have
been used for all AJ6 4.0 litre installations. The two systems are illustrated below.

FUEL DELIVERY AND EVAPORATIVE EMISSION CONTROL: XJ6 SEDAN RANGE 1990 MY

INJECTORS INTAKE
SWIRL CHAMBER MANIFOLD

FUEL TANK

FUEL
RAIL
PUMP FILTER

BYPASS VALVE

ECM

PURGE

COOL. TEMP.
ENG. LOAD
ENG. SPEED
CONTROL
PRESSURE / VACUUM VALVE
RELIEF VALVE

CHARCOAL
CANISTER
T800/1.04

FUEL DELIVERY AND EVAPORATIVE EMISSION CONTROL: XJ6 SEDAN RANGE 1991 – 94 MY; XJS RANGE 1993 – 94 MY

ROLL-OVER VALVE PRESSURE RELIEF VALVE

EVAPORATIVE
FLANGE FUEL
INJ.

RETURN FUEL
FILTER RAIL
FUEL PUMP
MODULE FUEL PUMP
FUEL PRESSURE
INLET PUMP REGULATOR
FILTER FILTER
VENT
FUEL TANK
FILTER

INTAKE
MANIFOLD

ECM
PURGE
VALVE

VACUUM / PRESSURE
RELIEF VALVE
(ROCHESTER VALVE)
COOLANT TEMP.

ENGINE SPEED

ENGINE LOAD

CHARCOAL
CANISTER

T800/1.05

8
System Description AJ6 4.0L Engine Management System

Fuel Delivery

A recirculating fuel system provides a continuous supply of pressurized, cooled fuel to the fuel
rail. There is sufficient fuel flow to allow full load engine operation at all times.

Fuel pump: XJ6 Sedan 1990 MY

Fuel is drawn from the fuel tank by an electric pump located on the rear subframe and is deliv-
ered to the fuel rail through a renewable filter mounted to the underbody. Unused fuel is returned
to the tank swirl chamber where it passes through a venturi before mixing with the remaining fuel
in the tank. This action cools the returning fuel.

FUEL PUMP: XJ6 SEDAN RANGE 1990 MY

HOUSING ROLLER

INLET OUTLET (PRESSURE SIDE)

PERMANENT
MAGNET

INLET
ROTOR
ROLLER CELL PUMP ELEMENT

NON-RETURN
VALVE

ROLLER CELL
PUMP

RELIEF VALVE

ARMATURE

OUTLET
T800/1.06

The in-line fuel pump is a roller type pump driven by a permanent magnet electric motor. An
eccentric rotor mounted on the armature shaft has metal rollers housed in pockets around the
circumference. When the motor is energized, centrifugal force acting on the rollers forces them
outward so that they act as seals. The fuel between the rollers is then forced to the outlet side
of the pump.

9
AJ6 4.0L Engine Management System System Description

Fuel Delivery and Evaporative Emission Control (continued)

Fuel Delivery (continued)

Fuel pump module: 1991 MY ON vehicles

The fuel pump is an integral component of an in-tank fuel pump module. The fuel pump module
mounts in a rubber holder attached to the bottom of the fuel tank on brackets. The fuel pump
module and the rubber holder are indexed to ensure correct alignment in the tank.

Fuel is drawn from the fuel tank through a 70 micron filter at the base of the module, then
through a 400 micron filter at the pump inlet. The pump delivers the fuel to the fuel rail through
a renewable in-line filter mounted to the underbody. Unused fuel is returned to the fuel pump
module where it passes through another 70 micron filter. A small portion of the pressurized fuel
flows through a venturi “teed” into the supply side inside the module. This flow enables a “jet
pump” to pick up fuel so that the module remains full at all times.

Both the outlet and return ports through the pump module have check valves. The outlet check
valve reduces back flow from the fuel rail when the pump is off. The return check valve holds fuel
pressure in the return line from the fuel rail and prevents siphoning if a fuel line is disconnected.

;
;;; ;
;;
FUEL PUMP MODULE: 1991 MY ON VEHICLES

FUEL RETURN FUEL SUPPLY

RETURN
FILTER
;;; ;;;;
;;; ;
CHECK VALVE

;;; ;
PUMP

;;; ;
;;; ;;; ;
“JET” PUMP
(BEHIND PUMP)

;;;
;;; ; “JET” PUMP

INLET FILTER
T800/1.07

10
System Description AJ6 4.0L Engine Management System

Fuel pump control

The electrically powered fuel pump is controlled by the ECM via the fuel pump relay. After the
ignition is turned on (position II), the pump runs for about 1 second to build fuel pressure for start-
ing. When the ECM receives an engine speed signal from the crankshaft position sensor, it
activates the fuel pump relay, which in turn switches on the fuel pump. The fuel pump will con-
tinue to run either until the ignition is turned off or until approximately 1 second after there is no
speed signal. The ECM monitors the output to the fuel pump relay for on-board diagnostics.

FUEL PUMP CONTROL

IGNITION ON EMS MAIN

RELAY RELAY

FUEL PUMP
RELAY

IGNITION INERTIA FUEL PUMP

SWITCH

ENGINE SPEED
(CRANKSHAFT SENSOR)

ENGINE CONTROL MODULE

NOTE: THIS DIAGRAM ILLUSTRATES CONTROL LOGIC FLOW ONLY;

REFER TO THE APPLICABLE WIRING DIAGRAM FOR POWER AND CIRCUIT INFORMATION. T800/1.08

NOTE: In the event of a vehicle collision, the inertia switch will switch off all ignition powered
circuits, including the EMS main relay. This action will remove power from the ECM and cause
the fuel pump relay to de-energize, switching off the fuel pump.

11
AJ6 4.0L Engine Management System System Description

Fuel Delivery and Evaporative Emission Control (continued)

Fuel Delivery (continued)

Fuel tank assembly: 1991 MY ON vehicles

The fuel pump module connects to the tank outlet and return ports via flexible hoses. Electrical
connection to the wiring harness is made through the evaporative flange.

FUEL TANK ASSEMBLY: 1991 MY ON VEHICLES

EVAPORATIVE
FLANGE

FUEL PUMP
MODULE

INDEX

FUEL LEVEL
RUBBER HOLDER TRANSMITTER

T800/1.09

12
System Description AJ6 4.0L Engine Management System

Fuel rail and pressure regulator

Fuel is pumped to the fuel rail and injectors, where fuel pressure is controlled by the fuel pres-
sure regulator. Excess fuel, above the engine requirement, is returned to the fuel tank. The
pressure regulator spring chamber above the diaphragm is referenced to intake manifold vacuum.
The differential pressure across the fuel injector nozzles is therefore maintained constant at
44 psi (3.0 bar) and the quantity of fuel injected for a given injector pulse duration is also constant.
Fuel pressure measured on a test gauge will vary between 32 psi (2.3 bar) at overrun to 44 psi
(3.0 bar) at full load.

The fuel pressure regulator is located as close as possible to the fuel rail so that good dynamic
control of fuel pressure is achieved. This design provides the same pressure across each injector,
and delivers an equal quantity of fuel to each of the six cylinders.

FUEL PRESSURE REGULATOR VACUUM (INTAKE MANIFOLD)

VACUUM (INTAKE MANIFOLD)

PRESSURE
SPRING

VALVE
DIAPHRAGM

FUEL SUPPLY

FUEL SUPPLY

FUEL RETURN
FUEL RETURN

T800/1.10

13
AJ6 4.0L Engine Management System System Description

Fuel Delivery and Evaporative Emission Control (continued)

Evaporative Emission Control: XJ6 Sedan 1990 MY

The fuel tank incorporates a plastic vessel that limits the fill level and allows for 10% fuel expan-
sion. Tank venting is via a system of vapor tubes and a liquid / vapor separator in the tank to the
charcoal canister, located in the left front wheel well. Vapor flow to the canister is controlled by
an engine vacuum-operated bypass valve which allows vapor flow to the canister when the
engine is operating. A pressure / vacuum relief valve prevents excessive pressure or vacuum
from building in the fuel tank. Canister purging to the intake manifold is controlled by the ECM
through an electric purge valve located at the canister.

Evaporative Emission Control: All models 1991 MY ON

The fuel tank is designed with a limited fill feature which allows about 10% fuel expansion. The
vapor pipe connected to the filler neck is connected into the tank at the maximum fuel level.
When the fuel covers the bottom of the vapor tube, fuel rises in the filler neck shutting off the
fuel delivery nozzle. Purging and control of vapor flow to the canister are identical to the 1990
model year system.

AJ6 4.0L EMS EVAPORATIVE EMISSION CONTROL (TYPICAL)

INTAKE MANIFOLD

PURGE PORT

PURGE
VALVE

ECM CHARCOAL
CANISTER

VACUUM
LINE
VACUUM / PRESSURE
RELIEF VALVE

EVAPORATIVE FLANGE

VAPOR
FLOW

FUEL TANK

T800/1.11

14
System Description AJ6 4.0L Engine Management System

Evaporative flange EVAPORATIVE FLANGE

The top of the fuel tank incorporates a remov-
able evaporative flange with three outlets. One CLOSED
outlet is used for the filler neck vent hose on
1991 model year vehicles and is capped-off on
later vehicles. The center outlet incorporates a
2.5 – 3 psi pressure relief valve and is con-
nected to a relief tube that vents to under the
vehicle. The third outlet incorporates a roll-over
valve and connects to the charcoal canister.
Electrical connection to the fuel pump module
is made through the evaporative flange.

CONNECTION TO
CHARCOAL CANISTER
OVERPRESSURE
VENT
T800/1.12

Vacuum / pressure relief valve

The flow of vapor to the canister is controlled by the vacuum / pressure relief valve (Rochester
valve). The valve has three functions: fuel tank pressure relief, fuel tank vacuum relief, and
vapor flow control.

When the vehicle is not operating and fuel temperature in the tank is increasing, vapor is released,
limiting the tank pressure to approximately 1 to 1.25 psi. When the vehicle is not operating and
fuel temperature in the tank is decreasing, a negative pressure is created. The umbrella check
valve in the vacuum / pressure relief valve allows vapor to flow back into the tank from the char-
coal canister, preventing the tank from collapsing. When the engine is operating, a manifold
vacuum signal, from the intake manifold, opens the valve allowing vapor flow to the canister and
reducing the fuel tank pressure to near zero. An additional fuel tank overpressure safeguard is
provided by a 4 psi relief valve in the fuel cap.

VACUUM / PRESSURE RELIEF VALVE

VACUUM (INTAKE MANIFOLD)

TO FUEL TANK TO CHARCOAL CANISTER

T800/1.13A, B

15
AJ6 4.0L Engine Management System System Description

Fuel Delivery and Evaporative Emission Control (continued)

Evaporative Emission Control: All models

Charcoal canister
CHARCOAL CANISTER
The charcoal canister contains activated char-
coal that absorbs the fuel tank vapors. As the
charcoal can become saturated, the canister is
purged of the collected vapors during engine
operation. Three ports are provided on the
canister: one for vapor flow in, one for purge
flow to the intake manifold, and one to allow
air to enter the canister during purging.
PURGE AIR INLET

FUEL TANK
VAPOR LINE
PURGE LINE

T800/1.14

Purge valve
PURGE VALVE The engine management ECM operates the
purge control valve to allow a regulated vapor
flow to the intake manifold dependent on
engine operating conditions. The purge valve
is a solenoid operated valve that is normally
open. The valve closing and subsequent rate
of vapor flow (opening) is varied by the
“length” of a pulsed electrical signal provided
from the ECM.

PURGE FLOW

T800/1.15

16
System Description AJ6 4.0L Engine Management System

Canister purging
The vapor adsorbed by the activated charcoal in the canister is purged by using engine vacuum
to draw air through the charcoal and into the intake manifold. The conditions during which
vapor is purged and the quantity purged is programmed into the ECM. The purge rate has to be
sufficient to prevent the charcoal canister from venting vapor to the atmosphere. On the other
hand, purge rates that are too high would cause driveability problems.

CANISTER PURGE CONTROL

IGNITION ON EMS MAIN ENGINE CONTROL MODULE

RELAY RELAY

CLOSED LOOP
IGNITION INERTIA FUEL METERING
SWITCH ENABLED

PURGE VALVE
COOLANT TEMP. ABOVE 93°F
(COOLANT TEMP. SENSOR)
ENGINE LOAD
(MASS AIR FLOW SENSOR, PURGE CONTROL
THROTTLE POSITION SENSOR) STRATEGY
ENGINE SPEED
(CRANKSHAFT SENSOR)

NOTE: THIS DIAGRAM ILLUSTRATES CONTROL LOGIC FLOW ONLY;

REFER TO THE APPLICABLE WIRING DIAGRAM FOR POWER AND CIRCUIT INFORMATION.
T800/1.16

Canister purge is enabled by the ECM when the engine coolant temperature exceeds 93°F (34°C)
and closed loop fuel metering control is operational. The rate of purge is determined from an
8 x 16 load versus engine speed strategy.

When the ignition is turned ON (engine inop- PURGE VALVE SIGNAL

erative), the valve is fully energized and closed
to prevent vapor flow to the engine. When
APPROX. 10 mSec. AT IDLE *
the engine is operating at idle and purge flow
is enabled, the purge flow will be small. As
engine load and speed increases, the purge
rate will increase proportionally. When the BATT. VOLTS

ignition is turned off the valve is fully energized

and held closed for a short period to prevent
vapor from being drawn into the engine as it APPROX. 140 – 145 mSec.
slows to stop to prevent run-on. Purge valve
operation at idle can be detected by holding
the valve in the palm of the hand. The ECM
monitors the output signal to the purge valve
for on-board diagnostics.

GROUND * This part of the signal increases in length

as the duty cycle / purge rate increases

T800/1.17

17
AJ6 4.0L Engine Management System System Description

Fuel Injection; Idle Speed Control

Fuel Injection

Fuel metering is obtained by controlling the injector pulse duration during each engine revolution.
The pulse duration is varied by the engine control module (ECM) according to several sensor
inputs. The sensed control inputs form two groups – primary and secondary. Primary control
inputs are intake mass air flow (engine load) and engine speed; secondary control inputs consist
of engine coolant temperature, cranking signal, throttle movement and position and exhaust
oxygen content. The injector pulse is then trimmed for battery voltage. Except during “crank-
ing” and rapid throttle application, all six injectors are pulsed once per engine revolution (twice
per engine cycle). Half of the fuel requirement is delivered at each pulse and the pulse duration
is recalculated before each succeeding injection.

Fuel metering strategies are held in memory (EPROM) in the ECM and form an engine load
versus engine speed matrix. The load and speed range of the engine is divided into 16 loads and
16 speeds (256 memory sites). Digital numbers representing injector pulse duration in millisec-
onds fill each site and cover the entire engine load and speed range.

NOTE: The sites are numbered 0 to 15 (16 total). Site 0 is less than overrun load, and low
engine speed. Site 15 is higher than full load and high engine speed. The load and speed sites
are purposely chosen to extend beyond the operational envelope of the engine.

INJECTOR WAVE FORM All fuel injectors are pulsed simultaneously by

the ECM “output stage”. To reduce power
consumption, the current drawn by the injec-
tors is controlled by the ECM. The injectors
are opened by a relatively large “turn on”
pulse and are held open for the required dura-
tion by a series of smaller “hold on” pulses.

Additional fuel injection controls are used for

overrun fuel cut-off, engine overspeed preven-
tion and wide-open-throttle during cranking
fuel cut-off.

BATT. VOLTS The ECM monitors its output signals to the

PULSE
DURATION fuel injectors and its input signals from sen-
sors for on-board diagnostics.

TURN ON
1.3 mSec.

CURRENT HOLD *

GROUND * Current hold section of wave form lengthens, adding more

switching cycles to provide the required pulse duration.

T800/1.19

18
System Description AJ6 4.0L Engine Management System

Fuel Injection Primary Control FUEL INJECTION PRIMARY AND SECONDARY CONTROL
ENGINE CONTROL MODULE
Fuel metering is controlled primarily as a func-
tion of engine load and speed. Engine load is
sensed by a mass air flow sensor located in ENGINE LOAD FUEL INJECTION
(MASS AIR STRATEGY
the engine air intake before the throttle hous- FLOW SENSOR)
ing. Engine speed is sensed by a crankshaft ENGINE SPEED
(CRANKSHAFT PRIMARY INJECTOR
sensor located behind the engine damper. In SENSOR) PULSE DURATION
addition to engine speed, the sensor supplies
crankshaft position inputs to the ECM for igni-
tion timing. The ECM processes the input CLOSED
LOOP EXHAUST OXYGEN
from the mass air flow meter and the crank- AIR / FUEL CONTENT
RATIO (OXYGEN SENSOR)
shaft sensor to access pulse duration from the
fuel metering strategy. Usually, the load and
speed at which the engine is running will be COOLANT TEMP. ENABLE / CANCEL
(COOLANT TEMP.
between sites. A function known as two SENSOR)
ACCELERATION WARM-UP COOLANT TEMP.
dimensional interpolation is used to calculate (THROTTLE POSITION STRATEGY (COOLANT TEMP.
SENSOR)
the correct pulse duration for the between- SENSOR)
FULL LOAD
sites engine condition. (THROTTLE POSITION
CORRECTION
FACTORS
SENSOR)
DECELERATION
(THROTTLE POSITION
SENSOR)
BATTERY
VOLTAGE BATTERY
CORRECTION VOLTAGE

INJECTOR
PULSE DURATION

CRANKSHAFT POS.
(CRANKSHAFT
SENSOR)
ENGINE CRANKING INJECTORS
(CRANKSHAFT TRIGGERED
SENSOR) SIMULTANEOUSLY
ACCELERATION
(THROTTLE POSITION
SENSOR)

FUEL INJECTORS
T800/1.20

LOAD SITES 4 & 12 versus ENGINE SPEED

6

LOAD SITE 12
5
MASS AIR FLOW SENSOR VOLTS

4 LOAD SITE 4

0
0 5 10 15 20 25 30 35 40 45 50 55 60 65
ENGINE SPEED (RPM X 100) T800/1.21

19
AJ6 4.0L Engine Management System System Description

Fuel injection; Idle Speed Control (continued)

Fuel Injection Secondary control
Secondary fuel metering control adjusts for engine coolant temperature, cranking signal, throttle
movement and position and exhaust oxygen content.

Cranking and after-start enrichment

The ECM provides fuel metering enrichment for cranking and after-start conditions.

The ECM recognizes engine cranking from the engine speed input (less than 200 rpm) and
increases the injector pulse frequency to three injection pulses per engine revolution. The pulse
duration is determined by engine coolant temperature. Cranking fuel metering is canceled at
250 rpm above a coolant temperature of 107°F (42°C) and at 500 rpm below the same tempera-
ture. At that point, injection reverts to one pulse per revolution and after-start enrichment is then
applied. The pulse duration, and the rate at which the enrichment is decreased back to the warm-
up phase is dependent upon engine coolant temperature.

Warm-up
The programmed warm-up enrichment provides extra fuel during engine warm-up based on the
engine temperature measured by the coolant temperature sensor. The injector pulse duration is
increased above the fully warm requirement when the coolant temperature is less than 186°F (85°C).

Acceleration enrichment
When the ECM senses that the throttle is opening (throttle position sensor input), the injector pulse
duration is lengthened by an amount dependent upon the rate at which the throttle is opened and
on engine coolant temperature. This acceleration enrichment prevents a momentary lean condi-
tion that can cause driveability or exhaust emission problems. If the throttle is opened rapidly, a
single “extra” injector pulse of about 5 milliseconds is generated to improve engine response.

Full load enrichment

If the ECM senses a full throttle input from the throttle position sensor, full load enrichment is
applied and closed loop operation is temporarily canceled.

Deceleration leaning
When the ECM senses that the throttle is closing (throttle position sensor input), the injector
pulse duration is shortened dependent on the rate at which the throttle closed. This action pre-
vents a momentary rich condition that can cause exhaust emission problems.

Summary of ECM functions based on throttle position sensor input:

Throttle Position ECM Function
Throttle closed (signal 0.25 – 0.75 volts) Idle speed control function
Ignition idle strategy
Overrun fuel cut-off
Idle fuel trim (adjustable mass air flow sensor
potentiometer only)
Adaptive idle fueling trim
Part throttle (signal above closed throttle Main fuel metering strategy
voltage and below full throttle voltage) Main ignition strategy
EGR enabled
Opening throttle (signal voltage increasing) Acceleration enrichment
Closing throttle (signal voltage decreasing) Deceleration leaning
Full throttle (signal greater than 3 volts) Full load enrichment (load dependent)
NOTE: Other sensor inputs are required for the initiation of most of the above listed ECM functions
as described in Fuel Injection, Idle Speed Control, Ignition, EGR and Adaptive Idle Fuel Metering.

20
System Description AJ6 4.0L Engine Management System

Closed loop operation OXYGEN SENSOR CHARACTERISTIC (HO2SRAW)

In order to significantly reduce exhaust emis-
sion, the exhaust system incorporates 3-way
catalytic converters that oxidize CO and HC,
and reduce NOx. These converters operate
800mV
efficiently only if engine combustion is as com-
plete as possible. It is generally accepted that
optimum combustion occurs with an air / fuel

OUTPUT VOLTAGE
ratio of 14.7 : 1 (Lambda = 1). A closed loop
system between fuel injection, ECM control
and exhaust oxygen content feedback is used
to maintain the air / fuel ratio as close to 14.7 : 1
as possible.

In response to the oxygen sensor voltage, the

ECM continuously drives the air / fuel ratio 200mV
rich-lean-rich by adding to, or subtracting from,
the injector pulse duration determined from
the main fuel metering strategy.
RICHER λ = 1 LEANER
Note that the oxygen sensor voltage switches
T800/1.22
abruptly at an air / fuel ratio of 14.7 : 1 (Lambda = 1).

Closed loop operation is canceled by the ECM

during the following functions:
• full load enrichment
• after-start enrichment
• warm-up (below 95°F [35°C])
• deceleration fuel cut-off

21
AJ6 4.0L Engine Management System System Description

Fuel injection; Idle Speed Control (continued)

Fuel Injection Secondary Control (continued)

Oxygen sensor feedback

Oxygen sensor feedback is an ECM output voltage that is used for technician monitoring of
closed loop operation. Oxygen sensor feedback can only be accessed through serial communi-
cations using JDS or PDU. The dampened or “average” feedback voltage is used to measure
the amount of “dynamic” correction applied by the ECM to the fuel metering strategy in
response to exhaust gas oxygen content.

NOTE: Oxygen sensor feedback may also be called Lambda feedback or integrator voltage.

The range for oxygen sensor feedback is 0 – 5 volts, representing a fuel metering strategy cor-
rection of -22% to +22%. The normal “average” feedback voltage is 2 – 3 volts.

Average oxygen sensor feedback voltage Correction (dynamic) applied by ECM

2.5 volts No correction is being applied. When

closed loop operation is canceled, the ECM
holds feedback at 2.5 volts.

Less than 2.5 volts The ECM is correcting for a rich condition
by subtracting from the injector pulse
duration held in the engine load / speed site.

Greater than 2.5 volts The ECM is correcting for a lean condition by
adding to the injector pulse duration held in
the engine load / speed site.

OXYGEN SENSOR FEEDBACK

IDLE FUEL MIXTURE

0 1 2 3 4 5
Current Oxygen Sensor Feedback (V)

2 3
Average Oxygen Sensor Feedback (V)

T800/1.23

Battery voltage correction

Because the time to achieve full lift of the injector pintle decreases as voltage increases, the
amount of fuel delivered by the injector for a given pulse duration is dependent upon the injec-
tor operating voltage.

The ECM is programmed with a voltage correction strategy. The supply voltage is monitored by
a software routine and the correction applied to the pulse duration.

22
System Description AJ6 4.0L Engine Management System

Additional Fuel Injection Controls

Overrun fuel cut-off OVERRUN FUEL CUT-OFF

In order to improve fuel economy and aid in
controlling exhaust emission, the ECM cancels ENGINE CONTROL MODULE
fuel injection during engine overrun conditions.
The ECM determines overrun conditions from
inputs received from the throttle position sen- THROTTLE CLOSED
(THROTTLE POSITION SENSOR) IF ENGINE SPEED
sor, crankshaft sensor and coolant tempera- FIRST REACHES
ture sensor. COOLANT TEMP. ABOVE 86°F 1500 RPM
(COOLANT TEMP. SENSOR)
FUEL INJECTION
With the throttle closed and the engine speed ENGINE SPEED ABOVE 1100 RPM CANCELLED
(CRANKSHAFT SENSOR)
above 1100 rpm, the ECM cancels fuel injec-
tion, provided that the coolant temperature is
above 86°F (30°C). The engine speed must
always reach 1500 rpm first for overrun fuel
NO FUEL INJECTION
cut-off to occur. In order to smooth the tran-
sition back to power, the ECM retards the
ignition timing and shortens the injector pulse T800/1.24

duration as the throttle opens and fuel injec-

tion is reinstated.
ENGINE OVERSPEED CONTROL
Engine overspeed control
An engine overspeed control function limits ENGINE CONTROL MODULE

the maximum engine speed to 6300 rpm by

canceling fuel injection. Fuel injection is rein-
stated at a slightly lower engine speed.
ENGINE SPEED 6300 RPM FUEL INJECTION
Wide-open-throttle during cranking (CRANKSHAFT SENSOR) CANCELLED
If the ECM senses that the throttle is wide
open (throttle position sensor input) during
cranking (less than 200 rpm), fuel injection is
canceled to help clear a flooded engine.

NO FUEL INJECTION

T800/1.25

WIDE-OPEN-THROTTLE DURING CRANKING

ENGINE CONTROL MODULE

THROTTLE WIDE OPEN

(THROTTLE POSITION SENSOR)

FUEL INJECTION
CANCELLED

ENGINE SPEED LESS THAN 200 RPM

(CRANKSHAFT SENSOR)

NO FUEL INJECTION

T800/1.26

23
AJ6 4.0L Engine Management System System Description

Fuel Injection; Idle Speed Control (continued)

Idle Speed Control

Idle speed is regulated by the motorized idle speed control valve that controls throttle bypass air.
The control valve is driven by the ECM. The ECM uses inputs received from ignition ON, the
crankshaft sensor, coolant temperature sensor and throttle position sensor as well as inputs for
gear position, air conditioning compressor operation and road speed to control idle speed.

ECM idle speed control occurs at closed throttle when road speed is less than 3 mph. The pro-
grammed idle speed accounts for engine temperature and the loads placed on the engine by the
transmission (gear position N, D, etc.), and air conditioning compressor clutch operation.

Typical controlled engine idle speeds

Cold engine (68°F [20°C]) / Neutral 800 rpm
Cold engine (68°F [20°C]) / Drive 650 rpm
Warm engine (193°F [90°C]) / Neutral 700 rpm
Warm engine (193°F [90°C]) / Drive 580 rpm

An ECM software function allows for a correction to the idle speed “base line” as the engine
base idle changes with age. The automatic adjustment values are held in RAM within the ECM
and will be retained or updated as long as the ECM is connected to battery voltage. If battery
voltage is removed for any reason, the stored correction values will be lost. The values will be
relearned only after the battery is reconnected, the engine operated from cold to normal oper-
ating coolant temperature at idle, and the vehicle driven for approximately 50 yards above 3 mph.

NOTE: At road speeds above 3 mph, the idle speed control valve is opened to limit overrun
intake manifold pressure. The amount that the valve is opened is based on engine speed and
throttle opening.

The ECM monitors its output signal to the idle speed control valve for on-board diagnostics.

24
System Description AJ6 4.0L Engine Management System

IDLE SPEED CONTROL

ENGINE CONTROL MODULE

THROTTLE CLOSED PARK; NEUTRAL

(THROTTLE POSITION SENSOR) (TRANS. CONTROL MODULE)

COOLANT TEMPERATURE IDLE SPEED A/C CLUTCH OPERATION

(COOLANT TEMP. SENSOR) STRATEGY (A/C CLUTCH CIRCUIT)

ENGINE SPEED ROAD SPEED 3 MPH OR LESS

(CRANKSHAFT SENSOR) (ROAD SPEED SENSOR)

STEPPER MOTOR DRIVE

T800/1.27

Engine start-up
ECM idle speed control begins shortly after the engine is started, provided the throttle is closed
(throttle position sensor at idle) and the road speed is less than 3 mph. The stepper motor in the
control valve is closed in stages until the target idle speed is reached.

Gear position
When the gear selector is moved to Park or Neutral from drive, the engine management ECM
receives a ground signal from the transmission rotary switch (XJS) or transmission decoder (XJ6
Sedan). The ECM then closes the idle speed control valve a predetermined number of steps in
anticipation of the reduced engine load. When the engine is at normal operating temperature,
the ECM maintains idle speed at 700 rpm in P or N and at 580 rpm in R, D, 2 or 3.

Air conditioning compressor clutch operation

When the air conditioning compressor clutch is energized, a parallel circuit inputs battery voltage
to the engine management ECM. The ECM opens the idle speed control valve a predetermined
number of steps to anticipate the change in engine load.

Ignition switched OFF

When the ignition is switched OFF, the control valve indexes to a known parked position. On
1990 model year vehicles, the reference is from the fully opened position. On later vehicles, the
reference is from the fully closed position, 7 seconds after the ignition is switched OFF.

25
AJ6 4.0L Engine Management System System Description

Fuel Injection; Idle Speed Control (continued)

Idle Trim (1990 – 1992 MY)

In order to compensate for slight differences from one vehicle to another, the ECM baseline to the
idle fuel metering strategy can be properly set with the mass air flow sensor idle trim potentiometer.

IDLE TRIM POTENTIOMETER

T800/1.28

26
System Description AJ6 4.0L Engine Management System

Adaptive Idle Fuel Metering (1993 MY ON Systems)

In order to ensure optimum performance, the ECM contains an adaptive idle fuel metering soft-
ware function that automatically makes a baseline correction to the idle fuel metering strategy,
throughout the life of the vehicle. The total available trim to the nominal injector pulse duration
is ± 10%. Adaptive idle fuel metering is performed by the ECM at idle, only when diagnostic
trouble codes (DTC) are cleared, and certain preconditions are met. If the DTCs are cleared and
the preconditions are met, the ECM cancels purge flow and adapts the fuel metering strategy.
Between adaptations, there is a delay of approximately eight minutes. The correction is applied
across the entire engine speed and load range.

NOTE: With the incorporation of adaptive idle fuel metering, the idle trim potentiometer was
removed from the mass air flow sensor.

Adaptive idle fuel metering preconditions:

• throttle is closed
• engine speed is below 1000 rpm
• road speed is below 3 mph (6 kph)
• engine coolant temperature is above 170°F (76°C)
• idle speed adaptive delay is complete (vehicle speed reached 3 mph for approximately
100 yards traveled)
• closed loop air / fuel ratio control is operating and in control
• oxygen sensor feedback (HO2SFB) voltage outside of the normal range (2 – 3 volts)

If the ECM loses its battery voltage supply for any reason, the stored correction will be lost and
fueling will revert to the programmed values.

27
AJ6 4.0L Engine Management System System Description

Ignition Timing Control

Ignition Timing
IGNITION TIMING PRIMARY AND SECONDARY CONTROL
Ignition timing is controlled by the engine con-
ENGINE CONTROL MODULE
trol module (ECM) according to sensor inputs.
As with fuel injection, the sensed control
ENGINE LOAD inputs form two groups: primary and second-
(MASS AIR FLOW SENSOR) IGNITION TIMING ary. Primary control inputs are intake mass air
STRATEGY
ENGINE SPEED flow (engine load) and engine speed; secondary
(CRANKSHAFT SENSOR) control inputs consist of engine intake air tem-
PRIMARY
CRANKSHAFT POSITION IGNITION TIMING perature, throttle movement and position and
(CRANKSHAFT SENSOR)
transmission upshift (automatic transmission).

Ignition timing strategies are held in memory

INTAKE AIR TEMPERATURE
(INTAKE AIR TEMP. SENSOR) (EPROM) in the ECM and form an engine load
versus engine speed matrix. The load and
THROTTLE MOVEMENT CORRECTION
(THROTTLE POSITION SENSOR) FACTORS speed range of the engine is divided into 16
TRANSMISSION SHIFT
loads and 16 speeds (256 memory sites).
(TRANS. CONTROL MODULE) Digital numbers representing ignition timing
values fill each site. The resulting 256 ignition
BATTERY
VOLTAGE timing values cover the entire engine load and
speed range. Ignition timing is then calculated
from the ignition timing strategy according to
ENGINE SPEED secondary input correction factors.
IGNITION TIMING
(CRANKSHAFT SENSOR)

The ECM drives the ignition module to switch

the ignition coil low tension circuit and moni-
tors the output signal for on-board diagnostics.

IGNITION MODULE Ignition Timing Primary Control

T800/1.29
Ignition timing is controlled primarily as a func-
tion of engine load and speed. Engine load is
sensed by a mass air flow sensor located in
ECM IGNITION OUTPUT SIGNAL TO IGNITION MODULE
the engine air intake before the throttle hous-
ing. Engine speed is sensed by a crankshaft
3 mSec. sensor located behind the engine damper. In
addition to engine speed, the sensor supplies
crankshaft position inputs to the ECM for igni-
tion timing. The ECM processes the inputs
from the mass air flow meter and the crank-
shaft sensor and accesses ignition timing from
4.6V the ignition timing strategy. Usually, the load
and speed at which the engine is running will
be between load and speed sites. Two
PIN 1
(BLUE) dimensional interpolation is used to calculate
GROUND the correct ignition timing for the between-
sites engine condition.
T800/1.30

28
System Description AJ6 4.0L Engine Management System

Ignition Timing Secondary Control

Secondary ignition timing control inputs consist of engine intake air temperature, throttle move-
ment and position, battery voltage and transmission upshift (automatic transmission).

Intake air temperature

Ignition timing is corrected by the ECM for engine intake air temperature measured by the air
temperature sensor mounted in the air inlet elbow. A portion of the ignition strategy (load sites
6 through 15; speed sites 4 through 15) is programmed with the temperature at which ignition
retard commences for each load / speed site. In general, light loads / low speeds have retard
thresholds set to a high temperature (approximately 212°F [100°C]) while high loads / high speeds
have retard thresholds set about 86°F (30°C). Above the threshold temperature, ignition timing
is retarded at the rate of 2.25° per 10°C.

Dwell angle
The dwell angle and peak coil current are controlled by the ignition module, located in the engine
compartment near the ignition coil. A feature called “stall turn-off” is used to prevent coil over-
heating and battery discharge. If the ignition switch is left on without the engine running, the
ignition module switches the coil current off.

Closed Throttle / Idle CLOSED THROTTLE / IDLE IGNITION TIMING CONTROL

There are separate closed throttle ignition ENGINE CONTROL MODULE

strategies for gear positions Neutral and Drive,

each with 8 speed break points for engine NEUTRAL DRIVE
(TRANS. CONTROL (TRANS. CONTROL
speed versus timing. With the engine at nor- MODULE) MODULE)
mal operating temperature, the Ignition timing CLOSED THROTTLE CLOSED THROTTLE
(THROTTLE POS. (THROTTLE POS.
at idle will be 10° BTDC in N (700 rpm) and SENSOR) CLOSED SENSOR)
16° BTDC in D (580 rpm). IDLE THROTTLE
COOLANT TEMP. IGNITION COOLANT TEMP.
IGNITION
(COOLANT TEMP. TIMING (COOLANT TEMP.
TIMING
SENSOR) STRATEGY SENSOR)
STRATEGY
ENGINE SPEED ENGINE SPEED
Ignition Secondary Circuit (CRANKSHAFT (CRANKSHAFT
SENSOR) SENSOR)
CRANKSHAFT POS. CRANKSHAFT POS.
The ignition secondary circuit consists of a (CRANKSHAFT (CRANKSHAFT
distributor and a standard ignition coil. The dis- SENSOR) SENSOR)

tributor contains only a rotor arm and a cap. BATTERY

VOLTAGE
The distributor must be correctly positioned to
index the rotor to the cap; however, it has no
affect on ignition timing. ENGINE SPEED
(CRANKSHAFT IGNITION TIMING
SENSOR)

IGNITION MODULE
T800/1.31

29
AJ6 4.0L Engine Management System System Description

Air Injection
Air Injection Operation

Air injection is used to promote reaction in the exhaust down pipe catalyst, reducing the time
required for the catalyst to reach working temperature. The air pumped into the exhaust mani-
folds mixes with exhaust gas and oxidation takes place. The heat generated in this process
reduces the time required for the catalyst to reach operating temperature.

Air injection is enabled by the ECM following each cold start and remains on until the engine
coolant temperature reaches 95°F (34°C). At 95°F the air injection circuit is switched off and
closed loop air / fuel ratio control is enabled. If the engine speed exceeds 2500 rpm while air
injection is enabled, the ECM will switch off the circuit.

On 1993 – 94 MY vehicles, air injection is also enabled for approximately 30 seconds after each
hot start.

AIR INJECTION
ENGINE CONTROL MODULE

ENGINE START
IF ENGINE SPEED
REACHES 2500 RPM AIR INJECTION
COOLANT TEMP. BELOW 95°F RELAY
(COOLANT TEMP. SENSOR)
AIR INJECTION
ENGINE SPEED CANCELLED
(CRANKSHAFT SENSOR)

MANIFOLD VACUUM

DELAY
VALVE SOLENOID VACUUM
VALVE

AIR CUT-OFF
CHECK VALVE VALVE AIR PUMP

T800/1.32

The ECM switches the air injection relay, which in turn switches both the air pump clutch and the
air injection solenoid vacuum valve. The solenoid vacuum valve controls the vacuum signal to the
air switching valve. The air switching valve performs two functions. It backs-up the air injection
check valve and it prevents air from being sucked through the pump and check valve into the
exhaust. Such leakage would cause an air / fuel ratio error at the oxygen sensor. The vacuum
supply to the air switching valve is sourced from the intake manifold through a delay valve. The
delay valve is used to ensure that the air switching valve is held open during short periods of high
engine load.

The ECM monitors its output to the air injection relay for on-board diagnostics.

30
System Description AJ6 4.0L Engine Management System

Exhaust Gas Recirculation

EGR Operation

Exhaust gas recirculation (EGR) is used to reduce the “oxides of nitrogen” (NOx) in the exhaust
during periods of high engine combustion temperatures (high loads and engine speeds). The
introduction of exhaust gas into the combustion chambers lowers the peak combustion tempera-
ture by reducing the volume of air / fuel mixture to be combusted.

The ECM both controls and monitors the operation of the system.

EXHAUST GAS RECIRCULATION

VACUUM (CONTROL)

EGR VALVE

EXHAUST GAS

EXHAUST MANIFOLD

INTAKE MANIFOLD

VACUUM EGR SOLENOID

VACUUM VALVE

EGR TEMPERATURE
SENSOR EGR ADAPTOR

COOLANT TEMPERATURE ABOVE 140°F

(COOLANT TEMPERATURE SENSOR)

ENGINE SPEED BETWEEN 1000 – 4000 RPM

(CRANKSHAFT SENSOR)
EGR CONTROL
STRATEGY
ENGINE LOAD NOT IDLE OR FULL LOAD
(MASS AIR FLOW SENSOR)

TRANSMISSION IN DRIVE GEAR

(DECODER MODULE [XJ6];
ROTARY SWITCH [XJS])

ON-BOARD
DIAGNOSTICS

ENGINE CONTROL MODULE

T800/1.33

31
AJ6 4.0L Engine Management System System Description

Exhaust Gas Recirculation (continued)

EGR Operation (continued)

EGR is enabled by the ECM when the following conditions exist:

• The engine coolant temperature exceeds 140°F (60°C)
• The engine is within a load / speed envelope that excludes idle and full load in the engine
speed range 1000 – 4000 rpm
• The transmission is in a driving gear (not P or N)

EGR OPERATING ENVELOPE

4.0

3.0
MASS AIR FLOW SENSOR VOLTS

2.0

EGR OPERATION
1.0

EGR GAS TEMPERATURE CHECK

0
0 10 15 20 25 30 35 40
ENGINE SPEED (RPM X 100)
T800/1.34

The ECM controls EGR by switching the EGR solenoid vacuum valve, which in turn, controls
vacuum application to the EGR valve. The vacuum operated EGR valve controls the flow of
exhaust gases between the exhaust and intake manifolds. Flow through the valve is proportional
to exhaust back pressure, which is itself proportional to engine load. Vacuum is applied to the
EGR valve via the ECM switched solenoid vacuum valve.

The ECM monitors its output to the EGR solenoid vacuum valve for on-board diagnostics.

The temperature of the exhaust gas flow to the intake manifold is also monitored by the ECM
for on-board diagnostics. Monitoring takes place over a load / speed range within the EGR
operational envelope.

32
System Description AJ6 4.0L Engine Management System

On-Board Diagnostics (OBD)

On-Board Diagnostic Facility (OBD I)

The ECM includes a fault diagnosis facility that continuously monitors the operation of the engine
management sensors and components. If a fault is detected, the OBD system will activate the
Malfunction Indicator Lamp (MIL) (CHECK ENGINE) warning in the instrument pack and flag a
diagnostic trouble code (DTC) in the ECM memory. The ECM can be interrogated through the
instrument pack LCD display (XJ6 Sedan Range) or center console LCD display (XJS Range). To
display the code, switch the ignition OFF; wait 5 seconds, then switch the ignition ON (do not
crank the engine). On Sedan Range vehicles, press the VCM button. On XJS Range vehicles,
a code is automatically displayed 5 seconds after the ignition is switched ON. The CHECK
ENGINE warning will display and the DTC will appear 5 seconds later. If two or more DTCs are
flagged in memory, only the highest priority code will be displayed. If the vehicle battery is dis-
connected, all stored codes will be cleared from the ECM’s memory. DTCs can also be accessed
via serial communication.

Limp Home Default

In order to allow vehicle operation if a malfunction occurs, “limp home” default values are incor-
porated as an ECM facility. If a sensor fault is detected by the OBD system, the ECM will
substitute a nominal value for the missing input(s) as follows:

Missing Sensor Input Default value

Engine coolant temperature 78° F (25° C)
Intake air temperature 86° F (30° C)
Mass air flow Throttle position (voltage) Vs. pulse duration
matrix; ignition timing = 8° BTDC @ idle,
20° BTDC above idle
Throttle position 1.5 volts
EGR temperature Switches off EGR
Oxygen sensor voltage Closed loop operation canceled
(feedback = 2.5 volts)
Idle trim adjustment (1990 – 1992 MY only) 2.5 volts

33
AJ6 4.0L Engine Management System System Description

On-Board Diagnostics (OBD) (continued)

Diagnostic Trouble Code Summary (listed in order of priority )

DTC Limp Home Fault Area JDS / PDU Description

Default
29 ECM self test Lucas injection ECM
44 X Oxygen sensor circuit HO2S / circuit
24 Ignition drive circuit IA drive circuit
12 X Mass air flow sensor circuit Mass air flow sensor / circuit
33 Injector drive circuit Fuel injector / circuit
34 Rich condition during Fuel injector leakage
overrun fuel cut-off
14 X Coolant temperature ETC Sensor / Circuit
sensor circuit
17 X Throttle position sensor circuit TP potentiometer / circuit
18 Throttle position sensor and TP / potentiometer / calibration 1
mass air flow sensor
(high throttle pos. voltage;
low air flow voltage)
19 Throttle position sensor and
mass air flow sensor TP / potentiometer / calibration 2
(low throttle pos. voltage;
high air flow voltage)
89 Purge valve drive circuit EVAP valve / circuit
26 Oxygen sensor feedback (lean) Air leak
37 EGR drive circuit EGR valve / circuit
39 X EGR temperature sensor circuit Exhaust gas temperature sensor
22 Fuel pump drive circuit Fuel pump / HO2S relay / circuit
23 Oxygen sensor feedback (rich) Fuel supply
46 Idle speed control valve IACV circuit, coil 1
(coil 1 drive circuit)
47 Idle speed control valve IACV circuit, coil 2
(coil 2 drive circuit)
48 Idle speed control valve IACV position error
11 X Idle fuel trim (1990 – 92 MY XJ6)
68 Road speed sensor circuit Vehicle speed sensor / wiring
69 Drive / Neutral input circuit PNPS / circuit
16 X Intake air temperature circuit IAT Sensor / Circuit
66 Air injection pump drive circuit AIR relay / circuit

NOTE: 1992 MY ON systems (ECM part no. DBC 9622 ON): In order to prevent incorrect flag-
ging of DTCs related to low fuel supply, fuel metering diagnostics are canceled when the fuel tank
level falls below approximately 2.5 gallons (11 litres).

34
System Description AJ6 4.0L Engine Management System

Vehicle Systems Interfaces

The engine management system interfaces with the transmission control module, the instrument pack and
the air conditioning compressor clutch circuit to provide operational control, sensor input and data input.

Transmission Control Module Interface

Engine torque reduction
The ECM receives two ignition timing retard inputs from the TCM: transmission shift “up /
down” signal (IGNITION SELECT) (pulsed signal), and transmission “shift in progress” signal
(IGNITION RETARD) (pulsed signal). Refer to Ignition Timing, page 29, for a detailed explanation.

Engine speed and load

The ECM outputs engine load and speed signals (PULSED SIGNALS) to the TCM. The TCM uses the
engine load and speed data to determine shift patterns and torque converter clutch apply and release.

Engine idle speed

The transmission decoder module (XJ6), rotary switch (XJS) outputs gear position signals to the ECM.
When the gear selector is in R, D, 2 or 3, the signal is 5 volts; when the gear selector is in P or N, the
signal is ground or 0 volts. The ECM uses the gear position inputs to control idle speed and for DTC 69.
Refer to Ignition Timing, page 29, and Idle Speed Control, pages 26 – 27, for a detailed explanation.

Instrument Pack Interface

Vehicle road speed
The instrument pack outputs a road speed signal (pulsed signal) to the ECM. The ECM uses the
signal to determine idle speed control functions.

Low fuel level (1992 MY ON [ECM part no. DBC 9622 ON])
The instrument pack outputs a fuel level voltage signal to the ECM. When the voltage drops
below 5.7 volts (2.5 gallons [11 litres] fuel remaining), fuel metering diagnostics (OBD) are can-
celed. Cancelling the fuel metering diagnostics prevents the ECM from flagging DTCs caused
by the vehicle running out of fuel.

Engine speed
Engine speed is output to the instrument pack for operation of the tachometer. Engine speed
is sensed from the ignition coil primary circuit (1990 – 92 MY Sedan and XJS). The ECM outputs
an engine speed signal (pulsed signal) to the instrument pack (1993 MY ON Sedan).

Fuel metering pulse

The ECM outputs a fuel metering pulse to the instrument pack for use by the trip computer
(average fuel consumption, instantaneous fuel consumption).

Fuel fail warning

If the OBD system detects a fault, the ECM outputs a fuel fail warning signal (ground) to the
instrument pack. Refer to On-Board Diagnostics, page 35.

Air Conditioning Compressor Clutch Interface

When the air conditioning compressor clutch is operating, a parallel circuit applies battery voltage
to the ECM. The ECM uses this signal to determine the need for idle speed control compensation.

Serial Communication
Serial communication between the engine management system and JDS or PDU is available. Serial
communication is used for engine setup, accessing stored DTCs, fault diagnosis and erasing DTCs.

35
36
EGR TEMPERATURE SENSOR
OXYGEN SENSOR EGR SOLENOID VACUUM VALVE FUEL RAIL AND INJECTORS IDLE SPEED CONTROL VALVE (UNDER MANIFOLD)
C.02G C.02H C.02I C.02J C.02L

EGR VALVE INTAKE AIR TEMPERATURE SENSOR

C.02F C.02K

DISTRIBUTOR THROTTLE POSITION SENS. (UNDER)

C.02E C.02M
AJ6 4.0L Engine Management System

EMS Components Installed on Engine

IGNITION COIL MASS AIR FLOW SENSOR

C.02C C.02N

C.02A

AIR INJECTION CHECK VALVE

IGNITION MODULE (UNDER MANIFOLD)
C.02D C.02O

AIR INJECTION SOLENOID VAC. VALVE COOLANT TEMPERATURE SENSOR CRANKSHAFT SENS. (FRONT PULLEY) AIR CUT-OFF VALVE (BEHIND PUMP) AIR INJECTION PUMP FUEL PRESSURE REGULATOR
C.02T C.02S C.02B C.02Q C.02R C.02P

XJ6 SEDAN RANGE SHOWN; XJS RANGE IDENTICAL

Component Location
Component Location AJ6 4.0L Engine Management System

EMS Components Installed on Vehicle

BLACK

YELLOW
FUEL PUMP
(IN TANK) FUEL PUMP FUEL PUMP RELAY
1991 - 94 MY 1990 MY FUEL FILTER 1991 - 92 MY
PURGE VALVE CHARCOAL
CANISTER

BLACK

GREEN

AIR INJECTION
PUMP RELAY
1990 - 92 MY
XJ6 SEDAN RANGE

LIGHT
ENGINE CONTROL LIGHT LIGHT LIGHT
BLACK BLACK
BLUE MODULE BLUE BLUE BLUE

BLACK RED YELLOW BLACK BLACK RED

FUEL PUMP EMS MAIN FUEL PUMP EMS MAIN OXYGEN SENSOR AIR INJECTION
RELAY RELAY RELAY RELAY HEATER RELAY PUMP RELAY
1993 - 94 MY 1990 - 92 MY 1990 MY 1993 - 94 MY 1993 - 94 MY 1993 - 94 MY

LIGHT
BLUE

GREEN

PURGE VALVE
FUEL PUMP FUEL FILTER FUEL FILTER FUEL PUMP RELAY CHARCOAL
(IN TANK) 1993 MY 1994 MY 1991 - 92 MY CANISTER

XJS RANGE

ENGINE CONTROL
SILVER/
SILVER MODULE RED
STRIPE

YELLOW RED

FUEL PUMP EMS MAIN

RELAY RELAY

37
AJ6 4.0L Engine Management System Component Description

Fuel Pump (XJ6 Sedan 1990 MY)

The in-line fuel pump is a roller type pump driven by a permanent magnet electric motor. An
eccentric rotor mounted on the armature shaft has metal rollers housed in pockets around the
circumference. When the motor is energized, centrifugal force acting on the rollers forces them
outward so that they act as seals. The fuel between the rollers is then forced to the outlet side
of the pump. A replaceable non-return valve is threaded into the pump outlet. The non-return
valve prevents fuel pressure loss when the pump is not running. The pump is located on the rear
suspension subframe.

FUEL PUMP: XJ6 SEDAN RANGE 1990 MY

HOUSING ROLLER

INLET OUTLET (PRESSURE SIDE)

PERMANENT
MAGNET

INLET
ROTOR
ROLLER CELL PUMP ELEMENT

NON-RETURN
VALVE

ROLLER CELL
PUMP

RELIEF VALVE

ARMATURE

OUTLET
T800/2.01

C.01

38
Component Description AJ6 4.0L Engine Management System

Fuel Pump Module (1991 MY ON vehicles)

The fuel pump is an integral component of an in-tank fuel pump module. The fuel pump module
mounts in a rubber holder attached to the bottom of the fuel tank on brackets. The fuel pump
module and the rubber holder are indexed to ensure correct alignment in the tank.

Fuel is drawn from the fuel tank through a 70 micron filter at the base of the module, then
through a 400 micron filter at the pump inlet. The pump delivers the fuel to the fuel rail through
a renewable in-line filter mounted to the underbody. Unused fuel is returned to the fuel pump
module where it passes through another 70 micron filter. A small portion of the pressurized fuel
flows through a venturi “teed” into the supply side inside the module. This flow enables a “jet
pump” to pick up fuel so that the module remains full at all times.

Both the outlet and return ports through the pump module have check valves. The outlet check
valve reduces back flow from the fuel rail when the pump is off. The return check valve holds fuel
pressure in the return line from the fuel rail and prevents siphoning if a fuel line is disconnected.

The inlet filter must not be folded or damaged and must be squarely mounted on its neck. If the
filter is damaged in any way, the fuel pump module must be replaced.

Fuel Pump Specifications

Speed 7000 rpm

;;
Flow rate 640 ml / 20 sec. @ 36 psi

;;;
Current 8 – 9 A @ 13.2 volts and 36 psi

FUEL PUMP MODULE: 1991 MY ON VEHICLES

;; ;;;;;;;;
FUEL RETURN FUEL SUPPLY

CHECK VALVE
RETURN

;; ;
FILTER

PUMP

;; ;
;; ;; ;
“JET” PUMP
(BEHIND PUMP)

INLET FILTER
;;;
;;; “JET” PUMP

T800/2.02

39
AJ6 4.0L Engine Management System Component Description

Fuel Pressure Regulator

Fuel is pumped to the fuel rail and injectors, where fuel pressure is controlled by the fuel pres-
sure regulator. Excess fuel, above the engine requirement, is returned to the fuel tank. The
pressure regulator spring chamber above the diaphragm is referenced to intake manifold vacuum.
The differential pressure across the fuel injector nozzles is therefore maintained constant at
44 psi (3.0 bar) and the quantity of fuel injected for a given injector pulse duration is also constant.
Fuel pressure measured on a test gauge will vary between 32 psi (2.3 bar) at overrun to 44 psi
(3.0 bar) at full load.

The fuel pressure regulator is located as close as possible to the fuel rail so that good dynamic
control of fuel pressure is achieved. This design provides the same pressure across each injector,
and delivers an equal quantity of fuel to each of the six cylinders.

FUEL PRESSURE REGULATOR VACUUM (INTAKE MANIFOLD)

VACUUM (INTAKE MANIFOLD)

PRESSURE
SPRING

VALVE
DIAPHRAGM

FUEL SUPPLY

FUEL SUPPLY

FUEL RETURN
FUEL RETURN

T800/2.03

The main component of the pressure regulator is the diaphragm, below which a steel ball valve
is mounted on a disc. The upper side of the diaphragm incorporates a spring retaining cup.
Spring length is set during manufacturing by deforming the top cover until the fuel pressure at
which the diaphragm lifts at atmospheric pressure is set at 44 psi (3.0 bar). A filter screen pre-
vents any small pieces of debris from the fuel rail becoming trapped under the disc.

The tube on the top of the upper case is connected to the intake manifold. During engine
operation, intake manifold vacuum “assists” the pressurized fuel to lift the diaphragm against the
spring. When fuel pressure exceeds the control value, the valve lifts off the seat allowing a
portion of the fuel to be directed to the outlet port, thereby maintaining fuel pressure at the con-
trol value. The excess fuel is returned to the fuel tank.

40
Component Description AJ6 4.0L Engine Management System

Purge Valve

The engine management ECM operates the purge control valve to allow a regulated vapor flow
to the intake manifold dependent on engine operating conditions. The purge valve is a solenoid
operated “duty cycle” valve that is normally open. The valve closing and subsequent rate of
vapor flow (opening) is varied by the “length” of a pulsed electrical signal provided from the ECM.
The resistance of the purge valve coil is approximately 42 ohms. The purge valve is located in
the left front fender arch, next to the charcoal canister.

PURGE VALVE

PURGE FLOW

PURGE FLOW

T800/2.04A, B

41
AJ6 4.0L Engine Management System Component Description

Fuel Injectors (1990 – 1992 MY)

The fuel injectors are solenoid operated valves that are pulsed by the ECM. The mechanical
design of the injectors incorporates a pintle valve with a waisted shape tip passing through the
orifice at the bottom of the injector body. The waisted shape of the pintle tip and orifice cause
the fuel flow to form a cone-shaped spray of small fuel particles. The fuel inlet at the top of the
injector has a small filter to trap any debris that may be present in the fuel. “O” Rings are used
to seal the injector between the fuel rail and intake manifold.

PINTLE-TYPE FUEL INJECTOR

SOLENOID WINDING

NOZZLE VALVE

T800/2.05A, B

INJECTOR WAVE FORM The electrical pulses applied to the injector coil
by the ECM attract the head of the pintle to
the coil armature. This action overcomes
spring pressure and allows fuel to flow
through the annulus between the pintle tip
and the orifice. Full valve lift (approximately
0.006 in) is reached in about 1 millisecond.
The resistance of the fuel injector coil is
approximately 2.5 ohms.

BATT. VOLTS
PULSE
DURATION

TURN ON
1.3 mSec.

CURRENT HOLD *

GROUND * Current hold section of wave form lengthens, adding more

switching cycles to provide the required pulse duration.

T800/2.06

42
Component Description AJ6 4.0L Engine Management System

Fuel Injectors (1993 MY ON)

The basic design and operation of the fuel injectors is similar to the earlier type; however, the
injector tips use a plate-type, twin-spray design. This design has several benefits: it aims a fuel spray
a each intake valve throat, it is quieter in operation, and the tip is less prone to contamination. The
injectors are secured to the fuel rail with custom clips that ensure the twin jets of fuel are directed
to the intake valve throats. A green band is used to identify the plate-type, twin-spray injector.

;;;;;
;;
TWIN-SPRAY FUEL INJECTOR

;;;;
;;;;;;
;;;;
NOZZLE VALVE SEAT FILTER

;;;;
;;;; ARMATURE
;;;;
;;;;COIL
ASSEMBLY
SPRING

T800/2.07A, B

43
AJ6 4.0L Engine Management System Component Description

Mass Air Flow Sensor

The mass air flow sensor, located in the intake tract downstream of the air cleaner, measures the
volume of air flow into the engine intake. The sensor has a cast alloy body with an integral elec-
tronic module. Some of the air flows through a bypass channel containing two small wire coils:

;;
; ;
a sensing coil and a compensating coil. The sensing coil is electrically heated by the electronic
module; the compensating coil remains unheated.

;;
; ;;
;
MASS AIR FLOW SENSOR
COMPENSATING SENSING

; ;;
COIL COIL

1990 – 92 MY ONLY

;;
;; ;
;;
;
;;;;
;;;
;
;;;
;
LOAD SITES 4 & 12 VERSUS ENGINE SPEED

6
;;; T800/2.08A, B

Intake air volume is determined by measuring

the electrical current required to keep the tem-
perature differential of the two coils constant.
This measurement occurs in the circuitry of the
LOAD SITE 12 sensor. The sensor then provides a voltage sig-
5 nal representing air flow to the ECM. The
theoretical full range of the signal is 0 – 5 volts.
MASS AIR FLOW SENSOR VOLTS

Idle voltage is normally 1.10 – 1.40 volts and

4 LOAD SITE 4
torque converter stall (full throttle; 1850 – 2150
rpm) voltage is normally 3.00 – 3.30.
3
On 1990 to 1992 MY vehicles, an adjustable
potentiometer is incorporated into the mass air
2 flow sensor to provide for idle fuel trim adjust-
ment during initial engine setup. This
potentiometer operates independently of the
1 air flow elements and provides a constant volt-
age signal to the ECM. The idle trim
potentiometer has an adjustment range of ap-
0
0 5 10 15 20 25 30 35 40 45 50 55 60 65
proximately 0 – 1000 ohms, measured
ENGINE SPEED (RPM X 100) between pins 1 and 6 of the mass air flow
T800/2.09
sensor connector. The ECM applies a 5 volt
reference to pin 6 and a ground to pin 1. With
the mass air flow sensor connected, the reference measured at pin 6 must be less than 4 volts
or DTC 11 will be flagged. Typically, the voltage is between 2 and 3 volts.

During 1994 MY, gold-plated connector pins were introduced to prevent corrosion and resistance
build-up. The gold-plated pins can be identified by their color.

CAUTION! Tin-plated pins and gold-plated pins must not be matched; they are not compatible.

44
Component Description AJ6 4.0L Engine Management System

Crankshaft Sensor

;;;;;;
; ; ; ; ; ;
CRANKSHAFT SENSOR SIGNAL

;;;;;;
CENTERLINE OF SENSOR
The crankshaft sensor provides both engine AT 8° ATDC
speed and crankshaft position signals to the
ECM. The sensor is a variable reluctance
device, consisting of a bobbin coil with a mag-
netic core. The resistance of the coil is MISSING TOOTH
7.5°
approximately 1.35 kilo ohms. The steel teeth
on the crankshaft timing ring are used as a
rotor. As the rotor teeth pass by the crank-
shaft sensor, pulses are generated. 13V*

The rotor has 60 tooth positions set at 6° inter- 9V*

vals with three teeth missing. The gaps
identify the TDC position of the 6 cylinders GROUND
during one complete engine cycle (two crank-
shaft revolutions). The rotor thus provides both
engine speed and crankshaft position informa-
tion to the ECM. The missing pulses identify * Identifies missing tooth
0.5° ATDC
crankshaft position. Each tooth pulse after the 3 times per engine revolution
T800/2.11
missing pulse represents 6° of crankshaft rota-
tion. Thus the frequency of the toothed
pulses are a measure of engine speed. The CRANKSHAFT SENSOR SIGNAL AT VARIOUS ENGINE SPEEDS
sensor is mounted to the timing cover on the
front of the engine. 10

CRANKSHAFT SENSOR 5
AC VOLTAGE

10
0
mSEC IDLE
10

5
AC VOLTAGE

5
T800/2.10

10
0
mSEC 1500 RPM
10

5
AC VOLTAGE

10
0
mSEC 2500 RPM

T800/2.12

45
AJ6 4.0L Engine Management System Component Description

Throttle Position Sensor

The throttle position sensor is a twin track design containing two separate potentiometer tracks
with wipers driven by a common spindle. The sensor is mounted on the throttle housing with
the spindle connected to the throttle shaft. One potentiometer track is used by the engine
management system; the other track is used by the transmission control system. Both poten-
tiometers have the same resistance, voltage and angle of rotation characteristics. The range of
resistance is approximately 500 ohms to 5.5 kilo ohms. The throttle position sensor provides a
voltage signal to the ECM that indicates throttle position and movement. The theoretical full
range of the signal is 0 to 5 volts.

The throttle position sensor output relative to the throttle valve position is set at closed throttle
using JDS or PDU. The ECM software function that recognizes closed throttle is “adaptive” and
will “learn” that voltage in a range from 0.25 to 0.75 volts is the closed throttle position. How-
ever, to avoid the ECM having to relearn the idle setting each time the battery is disconnected,
the idle voltage should be set very close to 0.6 volts.

THROTTLE POSITION SENSOR

T800/2.13

The ECM uses the voltage signal provided by the sensor for a number of ECM functions:

Throttle Position ECM Function

Throttle closed (signal 0.25 – 0.75 volts) Idle speed control function
Ignition idle strategy
Overrun fuel cut-off
Idle fuel trim (adjustable mass air flow sensor
potentiometer only)
Adaptive idle fueling trim
Part throttle (signal above closed throttle Main fuel metering strategy
voltage and below full throttle voltage) Main ignition strategy
EGR enabled
Opening throttle (signal voltage increasing) Acceleration enrichment
Closing throttle (signal voltage decreasing) Deceleration leaning
Full throttle (signal greater than 3 volts) Full load enrichment (load dependent)
NOTE: Other sensor inputs are required for the initiation of most of the above listed ECM functions.

46
Component Description AJ6 4.0L Engine Management System

Coolant Temperature Sensor

The coolant temperature sensor, located on the thermostat housing, is a negative temperature
coefficient (NTC) thermistor. NTC means that the resistance of the thermistor decreases as the
sensed temperature increases. Pin 1 of the sensor is connected to ground through the ECM. The
ECM applies 5 volts to pin 2 of the sensor and monitors the voltage across the sensor pins. The
theoretical full voltage range is from 5 to 0 volts representing maximum cold to maximum hot.

The ECM converts the monitored voltage into COOLANT TEMPERATURE SENSOR
a digital number that relates to an engine cool-
ant temperature. The temperature signal is
then used for a number of functions:
• Cranking enrichment
• Warm-up enrichment
• Acceleration enrichment
• Air injection
• Idle speed control
• Enable EGR
• Evaporative canister purge

NOTE: Other sensor inputs are required for

the initiation of most of the above listed ECM T800/2.14
functions.

Coolant temperature sensor – Coolant temperature sensor –

temperature versus resistance: temperature versus typical approximate voltage:
Coolant temperature Resistance Coolant temperature Voltage (measured at ECM Yellow
°F °C (kilo ohms) °F °C connector pin 2 or sensor pin 2)
14 -10 9.20 14 -10 4.05
32 0 5.90 32 0 3.64
50 10 3.70 59 15 2.89
68 20 2.50 78 25 2.42
86 30 1.70 86 30 2.20
104 40 1.18 104 40 1.78
122 50 0.84 122 50 1.44
140 60 0.60 140 60 1.17
158 70 0.435 158 70 0.95
176 80 0.325 176 80 0.78
193 90 0.25 193 90 0.65
212 100 0.19 212 100 0.55

47
AJ6 4.0L Engine Management System Component Description

Intake Air Temperature Sensor

The air temperature sensor, located in the air intake elbow, is a negative temperature coefficient
(NTC) thermistor. NTC means that the resistance of the thermistor decreases as the sensed tem-
perature increases. The air temperature sensor construction differs from the coolant temperature
sensor in that the thermistor element is exposed by holes in the tip of the housing. The holes
are designed to allow fast response in measuring air temperature changes while at the same time
providing the necessary mechanical protection. Pin 1 of the sensor is connected to ground
through the ECM. The ECM applies 5 volts to pin 2 of the sensor and monitors the voltage across
the sensor pins. The theoretical full voltage range is from 5 – 0 volts representing maximum cold
to maximum hot.

The ECM converts the monitored voltage into a digital number that is used to control the ignition
timing strategy. Refer to Ignition Timing Control on pages 29 – 31.

Intake air temperature sensor –

AIR TEMPERATURE SENSOR
temperature versus resistance:
Intake air temperature Resistance
°F °C (kilo ohms)
14 -10 9.20
32 0 5.90
50 10 3.70
68 20 2.50
86 30 1.70
104 40 1.18
122 50 0.84
140 60 0.60
158 70 0.435
176 80 0.325
193 90 0.25
212 100 0.19 T800/2.15

Intake air temperature sensor –

temperature versus typical approximate voltage:
Intake air temperature Voltage (measured at ECM Yellow
°F °C connector pin 20 or sensor pin 1)
14 -10 4.05
32 0 3.64
59 15 2.89
78 25 2.42
86 30 2.20
104 40 1.78
122 50 1.44
140 60 1.17
158 70 0.95
176 80 0.78
193 90 0.65
212 100 0.55

48
Component Description AJ6 4.0L Engine Management System

Oxygen Sensor

The oxygen sensor, located in the exhaust OXYGEN SENSOR CROSS SECTION
down pipe after the first catalyst, is a device
that produces voltage by conducting oxygen HEATER
HEATER CONNECTING WIRES
ions at temperatures above 572°F (300°C). In
order to reduce the amount of exhaust gas and
resulting emission needed to bring the sensor
up to working temperature, an internal electric
heater is used. The tip portion of the sensor
ceramic element is in contact with the exhaust
gas. The remaining portion of the ceramic ele-
ment is in contact with ambient air via capillary
action through the heater electrical wires.
CONTACT
ELEMENT SENSOR
OXYGEN SENSOR CONNECTING
ACTIVE SENSOR WIRE
PROTECTIVE TUBE CERAMIC
WITH SLOTS
T800/2.16B

OXYGEN SENSOR CHARACTERISTIC

800mV
OUTPUT VOLTAGE

T800/2.16A

The sensor voltage output switches between

approximately 800 millivolts and approximately
200 millivolts depending on the oxygen level
differential between ambient air and exhaust 200mV
gas on either side of the ceramic element.
When the air / fuel ratio is richer than 14.7 : 1
(Lambda = 1.0), the voltage output is high;
when the air / fuel ratio is leaner than 14.7 : 1 RICHER λ = 1 LEANER
T800/2.17
(Lambda = 1.0), the output voltage is low.
Only a very small change in air / fuel ratio is
required to switch the oxygen sensor.
OXYGEN SENSOR VOLTAGE TRACE: PDU HO2SRAW

0.86V

700mV
HO2SRAW

200mV

0V
6 TO 10 SWINGS PER MINUTE AT IDLE T800/2.18

49
AJ6 4.0L Engine Management System Component Description

Idle Speed Control Valve

The idle speed control valve assembly, located on the top of the intake manifold, contains a
manually adjusted base idle throttle bypass passage and an additional variable bypass passage.
The flow of bypass air through the variable passage is regulated by a stepper motor driven by the
ECM. The stepper motor has two coils that are pulsed by the ECM. The pulses are phased 90°
apart. The order in which the coils are pulsed determines the direction of stepper motor travel.
The coil resistance is approximately 50 ohms.

IDLE SPEED CONTROL VALVE BASE IDLE ADJUSTMENT

;;
STEPPER
MOTOR

;;
;
T800/2.19

;;
STEPPER MOTOR CROSS SECTION

;;;;;
;;;
;;;;;;;;;
;; ;;;
;;;;; ;;;;;;
;;;;;;;
T800/2.20

50
Component Description AJ6 4.0L Engine Management System

The stepper motor has a total travel from fully STEPPER MOTOR DRIVE SIGNAL
opened to fully closed of approximately 230 steps.

During engine setup (using JDS or PDU), the

BATT.
stepper motor is positioned at 200 steps from VOLTS
fully opened to allow the base idle speed to be
COIL A
set, using the manual air bypass screw. Once
the base idle speed is set correctly, the step-
per motor will hold the closed loop idle speed
within a few rpm of the nominal idle speed
(700 rpm in “N” and 580 rpm in “D”; normal
operating coolant temperature). GROUND

BATT.
VOLTS
When the ignition is switched off, the control
valve indexes to a known “parked” position. COIL B

On 1990 model year vehicles, the reference is

from the fully opened position. On later
vehicles, the reference is from the fully closed
position. GROUND

On 1993 and later model years, there is a T800/2.21

7-second delay after the ignition is switched

off before the control valve closes.

To accurately maintain a correct idle speed,

the ECM “learns” the idle stepper position. If
the ECM is disconnected from battery power,
the idle position must be relearned. The
simple way to allow the ECM to relearn the
position is to start the engine from cold and
allow it to idle until fully warm, then drive the
vehicle for a short distance.

51
AJ6 4.0L Engine Management System Component Description

AIR PUMP Air Pump

The mechanical rotary vane air pump is belt

driven through an electromagnetic clutch. The
clutch allows the pump to be engaged/disen-
gaged by the ECM (via the air injection relay.
If the engine speed exceeds 2500 rpm while
air injection is enabled, the ECM will switch off
the circuit to prevent over speeding the air
pump. Excessive back pressure would dam-
age the pump.

ELECTROMAGNETIC
CLUTCH
T800/2.22

AIR SWITCHING VALVE Air Switching Valve

The vacuum actuated air switching valve,

located behind the air pump, contains a spring-
loaded diaphragm valve resting on a seat.
When vacuum is applied, the diaphragm lifts
to allow air flow.

;;
;
;;;
;; ;;;
;;;;;
;;;
;;;;
;;;;
RETURN
VACUUM PORT SPRING

;;; ; DIAPHRAGM

;
FLOW ;; T800/2.23A, B

52
Component Description AJ6 4.0L Engine Management System

Air Injection Check Valve AIR INJECTION CHECK VALVE

The check valve, located in the delivery tube

behind the air pump, prevents the back-flow of
exhaust gas to the air pump.

;;;;
;;;
INLET
;;;;
;;;
;;;;
;;;
; ;;
;;;
;;;;
;;; PERFORATED FLEXIBLE DISK
DISK VALVE
T800/2.24

Air Injection Solenoid Vacuum Valve AIR INJECTION SOLENOID VACUUM VALVE

The air injection solenoid vacuum valve is

located at the left front corner of the engine.
When activated via the air injection relay, the
normally closed solenoid valve opens to apply
intake manifold vacuum to the air switching
valve. The resistance of the solenoid coil is
approximately 45 ohms.

MANIFOLD
VACUUM

AIR CUT OFF VALVE T800/2.25

53
AJ6 4.0L Engine Management System Component Description

EGR Valve

The EGR control valve is a “negative pressure” vacuum operated valve that compensates for
exhaust back pressure. The amount of exhaust gas flow into the intake manifold varies depend-
ing on intake manifold vacuum and variations in exhaust back pressure. The valve diaphragm has
an internal vacuum bleed hole that is held closed by a small spring when no exhaust back pres-
sure exists. When vacuum is applied via the solenoid vacuum valve, the EGR valve opens against
the pressure of the large spring. When intake manifold vacuum combines with negative exhaust
back pressure, the vacuum bleed hole opens to close the valve.

EGR VALVE EGR VALVE

T800/2.27

EGR VALVE OPERATION

FILTER SPRING
CONTROL VALVE SCREEN
(CLOSED)
CONTROL VALVE RESTRICTION
SPRING

VACUUM CHAMBER
VACUUM
SOURCE

AIR FLOW IN

DIAPHRAGM
DEFLECTOR

EXHAUST GAS TO
INTAKE MANIFOLD

EXHAUST GAS
EXHAUST GAS IN

T800/2.28 T800/2.26

54
Component Description AJ6 4.0L Engine Management System

EGR Solenoid Vacuum Valve EGR SOLENOID VACUUM VALVE

The EGR solenoid vacuum valve is located at

the rear of the intake manifold. When acti-
vated by the ECM, the normally closed
solenoid valve opens to apply intake manifold
vacuum to the EGR valve. The resistance of
the solenoid coil is approximately 45 ohms.

MANIFOLD
VACUUM

EGR VALVE
T800/2.29

EGR Temperature Sensor EGR TEMPERATURE SENSOR

The EGR sensor is a negative temperature

coefficient (NTC) thermistor. NTC means that
the resistance of the thermistor decreases as
the sensed temperature increases. The ECM
applies 5 volts to pin 1 of the sensor and moni-
tors the voltage across the sensor pin to
ground. The theoretical full voltage range is
from 5 to 0 volts representing maximum cold
to maximum hot. Typically, with the engine
running at 2000 rpm, the sensor voltage will
drop 0.1 volt when the EGR valve is opened.

EGR temperature sensor –

T800/2.30
temperature versus resistance :
Intake air temperature Resistance
°F °C (kilo ohms)
122 50 600
212 100 90
302 150 11
392 200 5
482 250 2
572 300 0.8
662 350 0.3
752 400 0.1

55
AJ6 4.0L Engine Management System Component Description

IGNITION MODULE Ignition Module

The ignition module is controlled by the ECM

output signal and switches the ignition coil pri-
mary circuit. The dwell angle and peak coil
current is also controlled by the ignition module.
A feature called “stall turn-off” is used to prevent
coil overheating and battery discharge if the igni-
IGNITION MODULE tion is left on without the engine running.

NOTE: 1990 model year systems have a four-

wire (plus ground) ignition module. 1991 ON
model year systems have a three-wire (plus
ground) ignition module. The modules are
interchangeable.

The module is mounted to an aluminum heat

sink plate. If the module and heat sink are sepa-
rated, heat sink compound must be applied
between the components upon reassembly.

HEAT SINK

T800/2.31

IGNITION DISTRIBUTOR Ignition Distributor

The distributor is a standard unit containing

only a rotor arm and cap to distribute high volt-
age to the spark plugs. The distributor has no
effect on ignition timing and can be considered
as a simple rotating switch. It is necessary
only to position the distributor for correct rotor-
to-cap alignment at TDC.

T800/2.32

56
The following Figures and Data pages are extracted from select
Electrical Guides and are included here as an
aid to understanding the Engine Management system.
Do not use this information to diagnose vehicle faults.

Always refer to the Model and Model Year specific

Electrical Guide for accurate information.
6.0 Litre V12 / ND Engine Management System

Contents

Overview 1

On-Board Diagnostic Facility – OBD II 2–4

Engine Control Module 5–9

EMS Component Location 10 – 11

Fuel Delivery and Evaporative Emission Control 12 – 19

Fuel Injection 20 – 23

EMS Main Sensing Components 24 – 35

Ignition Control 36 – 40

Idle Control 41 – 43

Secondary Air Injection (AIR) 44 – 47

Catalytic Converters 48

Engine Misfire 49

Vehicle Systems Interfaces 50 – 51

Crankcase Emission Control 52

i
 6.0 Litre V12 / ND Engine Management System

Overview
The Jaguar 6.0 litre V12 / ND (Nippon Denso) Engine Management System (EMS), introduced in the
1995 Model Year XJ12 Sedan, is controlled through a digital Engine Control Module (ECM) containing
a microprocessor. The system maintains optimum performance by precisely controlling all fuel injec-
tion, ignition and emission control functions. In addition, the ECM provides various interface outputs
and incorporates an on-board diagnostic facility.

The V12 / ND EMS complies with OBD II (on-board diagnostics II), the second generation environmen-
tal legislative regulations that set the acceptable maximum level of motor vehicle exhaust emission and
the engine control systems self diagnosis capabilities.

The V12 Lucas / Marelli EMS complies with OBD I. Generally, the operating standards for the two OBD
systems are as follows:

OBD I (V12 Lucas / Marelli EMS)

• Regulated exhaust emission level
• Monitoring and diagnosis of electrical fuel system faults
• Monitoring of both open and closed circuit faults
• Visual warning to driver: MIL (CHECK ENGINE)
• Fault code available to technician: Diagnostic Trouble Code — DTC (Fuel Fail Code — FF)

OBD II (V12 / ND EMS)

• Reduced exhaust emission level
• Industry standardized DTCs
• Generic (after-market) scan tool capable of DTC retrieval
• Expanded self diagnostics to include monitoring and diagnosis of any power train system fault that
will likely cause exhaust emission to exceed 1.5 times the standard level.
• Failure prediction of subsystems by performance observation over the life of the power train including:
catalyst efficiency, engine misfire, and secondary air injection.

NOTES

1
6.0 Litre V12 / ND Engine Management System

On-Board Diagnostic Facility – OBD II

The OBD facility has expanded diagnostic capabilities to continuously monitor the operation of the
engine management sensors and components. In addition, the facility predicts failure of subsystems
by performance observation. If a fault is detected by OBD monitoring or testing, it is registered in the
ECM internal software. The ECM decides whether to flag a DTC and activate the CHECK ENGINE MIL
(Malfunction Indicator Light).

Faults stored in the ECM memory can only retrieved through serial communication via the data link.
DTCs are held in memory (RAM) that requires vehicle battery power to remain activated. Disconnect-
ing the vehicle battery will erase all stored codes.

DATA LINK CONNECTOR Engine Management Faults

Except in cases where vehicle operation would
be seriously impaired, a fault must be detected
on two consecutive trips before the CHECK EN-
GINE MIL will activate. After the MIL is
activated, if three sequential trips are made with
no recurrence of the fault(s) and no occurrence of
additional fault(s), the MIL will extinguish on the
next trip. The fault(s) will remain stored in
memory. The ECM will erase any fault code that
does not recur after 40 consecutive engine
warm-up cycles.
T851 / 4.70

Transmission Faults
Upon detection of a transmission fault, the TCM activates the TRANSMISSION MIL immediately, and
signals the ECM to activate the CHECK ENGINE MIL and store an engine management DTC. If the
transmission fault is “self corrected”, the TRANSMISSION MIL will extinguish at the end of the drive
cycle; however, the CHECK ENGINE MIL will remain activated for an additional three consecutive fault-
free trips. The engine management DTC will be erased after 40 fault-free engine warm-up cycles.

Trips and Service Drive Cycle

“Trip” and “Service Drive Cycle” are terms used in conjunction with OBD II.

A “Trip” means vehicle operation, following an engine-off period, of duration and driving mode such
that all EMS components and subsystems are checked at least once by the diagnostic system, with
the exception of catalyst efficiency monitoring. Catalyst efficiency and evaporative system monitoring
require a steady vehicle speed check.

NOTES

2
 6.0 Litre V12 / ND Engine Management System

Trip Test
To test all of the EMS components and subsystems, the trip test procedure must be followed twice,
with an engine stop between to allow the two-trip logic to operate and a DTC to be stored.

Trip test procedure:

1 Turn off the air conditioning system.
2 Start the engine and idle for 20 seconds.
3 Wait for the engine to warm up to a coolant temperature of greater than 80˚C.
4 Idle the engine for two minutes without turning the steering wheel or operating electrical loads.
5 Drive the car as described below, with the gear selector in “D” unless otherwise stated. The specified
speeds are targets. If the actual speed is not more than 2 mph different from the target, the test
will be performed correctly. Hold a steady throttle position and drive on a level road.
• Accelerate to 34 mph and drive steadily at this speed for 1 minute.
• Accelerate to 44 mph and drive steadily at this speed for 10 seconds.
• Accelerate to 56 mph and drive steadily at this speed for 1 minute.
• Drive for over 10 seconds with the engine above 3000 rpm (select a lower gear to limit vehicle
speed).
• Brake gently to a stop.
• Accelerate to 22 mph and then brake to a stop. Repeat this step four times.
6 Switch the engine off.
7 Interrogate the ECM for stored codes, first with the key on and the engine off, then with the engine idling.

Service Drive Cycle Test

To check for a reoccurrence of a particular DTC, a vehicle must be operated over a “Service Drive
Cycle”. A “Service Drive Cycle” is a planned routine of operating a vehicle so that the components
and subsystems that are being monitored by a particular code will be tested. For certain DTCs, such
as that for the engine coolant temperature sensor (ECTS), the Service Drive Cycle is simple and
includes:
• ignition ON
• engine start
• engine run to normal operating temperature
• ignition OFF

More complex diagnostic routines require additional operating modes. For a full list of operating modes,
required for each code, refer to the DTC Summary on pages 53 – 62.

NOTES

3
6.0 Litre V12 / ND Engine Management System

On-Board Diagnostic Facility – OBD II (continued)

Systems Readiness Test
It can be determined if the Service Drive Cycle was of sufficient length to test for DTC reoccurrence
by performing a PDU “Systems Readiness Test”.

The Systems Readiness Test occurs automatically when the PDU reads the DTCs from the ECM memory
and reports if a full OBD check has or has not been completed since the memory was last cleared.
If code P1000 is stored in memory, the on-board diagnostic tests have not been completed.
If code P1111 is stored in memory, the on-board diagnostic tests have been completed.

OBD II Reports to Jaguar Cars

Whenever the CHECK ENGINE MIL is activated, a DTC and accompanying “freeze frame” data will
be stored in the ECM memory. This information must be retrieved using the PDU “OBD II Report”
and reported to Jaguar Cars on form S93.

Limp Home Default

In order to allow vehicle operation if a malfunction occurs, “limp home” default values are incorporated
as an ECM facility. If a sensor fault is detected by OBD, the ECM will substitute a nominal value for
the missing input(s). The ECM contains default strategies / values for the following:
• Manifold absolute pressure sensors (MAPS) • Heated oxygen sensors (HO2S)
• Camshaft position sensor (CMPS) • Ignition control modules
• Throttle position sensor (TPS) • Evaporative control valves (EVAPP valves)
• Engine coolant temperature sensor (ECTS) • Fuel pump 1
• Crankshaft position sensor (CKPS) • High altitude correction sensor (HACS)
• Intake air temperature sensor (IATS)

Diagnostic Trouble Codes

The number of possible diagnostic trouble codes (DTCs) has been greatly increased. Each DTC is a
five place standard SAE (Society of Automotive Engineers) code that describes a subsystem and the
specific fault. Refer to the DTC Summary on pages 53 – 62 for a complete DTC listing including moni-
toring conditions and possible faults.

DTCs are arranged in seven major groups as follows:

PX1XX Fuel and air metering
PX2XX Fuel and air metering
PX3XX Ignition system or misfire
PX4XX Auxiliary emission controls
PX5XX Vehicle speed; idles control; auxiliary inputs
PX6XX Computer and auxiliary inputs
PX7XX Transmission control

NOTES

4
 6.0 Litre V12 / ND Engine Management System

Engine Control Module

The V12 / ND EMS is microprocessor based using
V12 / ND ECM
a unique Nippon Denso ECM as the heart of the
system. The ECM has a 128 megabyte memory
with a microprocessor running at a clock speed of
4 MHz. The ECM uses discrete components plus
analog-to-digital circuits to interface between the
microprocessor and the input sensors and output
devices. Software is programmed into an
EPROM used for control, data, On-Board Diagnos-
tics and adaptive functions.

The ECM controls the engine management sys- PI44

PI45
tem as two separate systems (A bank, B bank) or
PI47
as one twelve cylinder system depending on en- PI46 T851 / 4.01
gine operating conditions and diagnostic functions.

A nonvolatile memory is used to store the vehicle identification number (VIN). Quiescent current is used
to keep the ECM random access memory (RAM) active so that OBD generated DTCs and adaptive
values are maintained. If the vehicle battery is disconnected, the ECM will “relearn” adaptive values
during the next driving cycle

CAUTION: ECMs must not be switched from one vehicle to another because the VIN will be mismatched.

The ECM contains four connector sockets. A rough guide to the connector function grouping is as
follows: the 28-way connector (PI44) carries the ECM to vehicle interfaces; the 16-way connector (PI45)
carries the EMS sensor inputs; the 22-way connector (PI46) carries the EMS signal inputs and outputs;
the 34-way connector (PI47) carries the EMS actuator outputs and most of the grounds.

Specific variants (Federal, ROW) are achieved through PECUS (programmable electronic control units)
programming of the ECM EPROM during manufacturing.

If a replacement ECM flashes the CHECK ENGINE MIL when the ignition is switched to position II,
PECUS programming has not been carried out.

ECM monitoring for OBD II

Each time the ignition is switched ON, the ECM checks its memory for corrupted data. If a fault is
found, a DTC is flagged and the CHECK ENGINE MIL is activated immediately. The CHECK ENGINE
MIL will remain lit after the engine is started. Refer to DTC Summary: Groups 23 and 25, page 62.

High altitude correction

A high altitude correction sensor (HACS) that senses barometric pressure is incorporated into the ECM.
The HACS input is used for high altitude fuel metering correction, OBD diagnostic information, and idle
speed control correction. The HACS cannot be replaced separately.

HACS monitoring for OBD II

The HACS is checked for a continuous high or low signal. If there is a fault, a DTC will be flagged and
the CHECK ENGINE MIL will be activated immediately. The sensor is also monitored with the engine
running by comparison with the MAP sensor signals. If the value is too high or too low compared to
the MAPS signals, a DTC will be flagged. The fault must occur on two consecutive trips before the
CHECK ENGINE MIL will be activated. Refer to DTC Summary: Group 7, pages 54 and 58.

NOTES

5
6
FUEL PUMP RELAY 1
FUEL PUMP RELAY 2
ECM FUEL
LEVEL
SENSOR

FILTER
FUEL FUEL
PUMP 1 PUMP 2

FUEL TANK ECM

TPS
FUEL FUEL
SUPPLY RETURN
IGNITION MODULES

ECM ECM
V12 / ND ENGINE MANAGEMENT LOGIC

ECM MAPS MAPS

FUEL PRESS.
ECM REGULATOR ECM
IATS

FI FI

ECM
IACV CMPS IACV
AIRP
AIRP
IGN. COILS ECM
ECM ECM ECM PRESSURE
ECTS CONTROL
RPM VALVE
SENS.
ECM EVAPP EVAPP ECM
Engine Control Module (continued)

ECM ECM

HO2S A BANK B BANK HO2S

UPSTREAM UPSTREAM
6.0 Litre V12 / ND Engine Management System

EVAPORATIVE
CANISTER

ECM ECM
CKPS
HO2S HO2S
DOWNSTREAM DOWNSTREAM

ECM

T851 / 4.02A
 6.0 Litre V12 / ND Engine Management System

V12 / ND ENGINE MANAGEMENT LOGIC

FUEL INJ. BATTERY POWER

FUEL INJECTOR
POWER SUPPLY RELAY
(MAIN RELAY) IGNITION SWITCHED POWER

BATTERY POWER
IGNITION IGNITION
POWER SUPPLY COIL RELAY
IGNITION SWITCHED POWER
EXHAUST PORTS AIRP

FUEL PUMP 1 FUEL PUMP 2

AIRP FUEL PUMP FUEL PUMP

RELAY RELAY 1 RELAY 2

RPM SENSOR BATTERY POWER

MAPS IGNITION SWITCHED POWER

ECTS

CKPS

CMPS

TPS

IATS BPM (CRANK SIGNAL)

H02S TRANSMISSION
(TORQUE CONTROL)

FUEL INJECTORS TRANSMISSION

(THROTTLE POSITION)

IGNITION TRANSMISSION
(GEAR SELECTOR POSITION)

HO2S HEATERS CLIMATE CONTROL

(A/C COMPRESSOR CLUTCH OPERATION)

IACVs ELECTRICAL LOAD

(HEATED WINDSHIELDS, BLOWERS HIGH SPEED)

EVAPPs SERIAL COMMUNICATIONS

FUEL LEVEL VEHICLE SYSTEMS INTERFACE

HACS (VEHICLE SPEED, ENGINE SPEED, FUEL INFO)
POWER STEERING CHECK ENGINE
PRESSURE

OBD II MONITORING

ENGINE CONTROL MODULE

KEY TO ACRONYMS (THIS PAGE AND PAGE AT LEFT)

AIRP SECONDARY AIR INJECTION PUMP HO2S HEATED OXYGEN SENSOR
CKPS CRANKSHAFT POSITION SENSOR IACV IDLE AIR CONTROL VALVE
CMPS CAMSHAFT POSITION SENSOR IATS INTAKE AIR TEMPERATURE SENSOR
ECM ENGINE CONTROL MODULE KS KNOCK SENSOR
ECTS ENGINE COOLANT TEMPERATURE SENSOR MAPS MANIFOLD ABSOLUTE PRESSURE SENSOR
EVAPP EVAPORATIVE EMISSION CONTROL (PURGE) VALVE RPM SENS. ENGINE SPEED SENSOR
FI FUEL INJECTOR TPS THROTTLE POSITION SENSOR
HACS HIGH ALTITUDE CORRECTION SENSOR
T851 / 4.02B

7
6.0 Litre V12 / ND Engine Management System

Engine Control Module (continued)

V12 / ND ECM

10 1 6 1 4 1 8 1
16 11 11 7 7 5 13 9
26 17 17 12 11 8 21 14
34 27 22 18 16 12 28 22
PI47 PI46 PI45 PI44
T851 / 4.03

Engine Control Module Pin Out Information

I = Input O = Output SG = Signal Ground D = Serial Communications
I/O Pin Description
O PI44-1 Fuel used
O PI44-2 Check engine MIL
O PI44-3 Engine torque signal
O PI44-4 Throttle position
O PI44-5 Load inhibit signal
I PI44-6 Torque reduction
I PI44-7 Vehicle speed
O PI44-10 Engine speed
I PI44-12 Electrical load: Heated windshield, heated backlight or blowers on high speed
I PI44-13 Air conditioning request
D PI44-14 Not used
I PI44-18 Park / neutral
I PI44-21 Fuel level
D PI44-22 Serial communication input
D PI44-23 Serial communication output
PI44-24 Battery power supply
PI44-25 Ignition switched power supply
PI44-26 Flexible fuel select link (dealer fit)
PI44-28 Ground (signal)

I PI45-1 MAP sensor feedback – B bank

I PI45-2 MAP sensor feedback – A bank
I PI45-3 Idle switch
I PI45-4 Throttle position sensor feedback voltage
I PI45-5 Coolant temperature sensor
I PI45-6 Intake air temperature sensor
O PI45-7 Common sensor reference voltage
I PI45-8 Downstream HO2S feedback – B bank
I PI45-9 Downstream HO2S feedback – A bank
I PI45-10 Upstream HO2S feedback – B bank
I PI45-11 Upstream HO2S feedback – A bank
PI45-12 Ignition switched power supply

8
 6.0 Litre V12 / ND Engine Management System

I/O Pin Description

I PI45-13 Power steering pressure switch
PI45-14 Ground (signal)
SG PI45-15 Common sensor shield ground
SG PI45-16 Common sensor reference ground

O PI46-3 Downstream HO2S heater ground – B bank

O PI46-4 Downstream HO2S heater ground – A bank
O PI46-5 Upstream HO2S heater ground – B bank
O PI46-6 Upstream HO2S heater ground – A bank
I PI46-7 Crank signal
I PI46-8 Camshaft position sensor
PI46-10 Ground
PI46-11 Ground
SG PI46-12 Camshaft position sensor
I PI46-13 Crankshaft position sensor
I PI46-14 Engine speed sensor
O PI46-16 A/C compressor clutch relay
O PI46-17 Secondary air injection relay
SG PI46-18 Crankshaft position sensor
SG PI46-19 Engine speed sensor
I PI46-20 Ignition failure – B bank
I PI46-21 Ignition failure – A bank
PI46-22 Ground

O PI47-1 Idle air control valve close – B bank

O PI47-2 Idle air control valve open – B bank
O PI47-3 Idle air control valve close – A bank
O PI47-4 Idle air control valve open – A bank
O PI47-5 Fuel injectors 3 & 5 – B bank
O PI47-6 Fuel injectors 2 & 4 – A bank
O PI47-7 Fuel injectors 1 & 4 – B bank
O PI47-8 Fuel injectors 3 & 6 – A bank
O PI47-9 Fuel injectors 2 & 6 – B bank
O PI47-10 Fuel injectors 1 & 5 – A bank
O PI47-11 Secondary air vacuum solenoid valve
O PI47-12 Fuel pump relay 2
PI47-13 Ground
PI47-14 Ground
PI47-15 Ground
PI47-16 Ground
O PI47-17 Ignition module negative – 3B
O PI47-18 Ignition module negative – 2B
O PI47-19 Ignition module negative – 1B
O PI47-20 Ignition module negative – 3A
O PI47-21 Ignition module negative – 2A
O PI47-22 Ignition module negative – 1A
PI47-23 Ground
PI47-26 Ground
PI47-27 Ground
PI47-28 Ground
O PI47-29 Fuel pump relay 1
O PI47-33 EVAP valve – B bank
O PI47-34 EVAP valve – A bank

9
6.0 Litre V12 / ND Engine Management System

EMS Component Location

EMS COMPONENT CONNECTOR LOCATIONS

1 2 3 4 5 6 7 8 9 6 10 11 14 15

12
28 13

27
16
26

25
24
17

22 23 21 20 19 18

KEY TO ILLUSTRATION
(ALSO APPLIES TO ILLUSTRATION AT RIGHT)
1 FUEL PUMP 1 18 ENGINE COOLANT TEMPERATURE SENSOR (ECTS)
2 FUEL LEVEL SENSOR 19 FUEL PRESSURE REGULATOR
3 FUEL PUMP 2 20 A BANK IDLE AIR CONTROL VALVE (IACV)
4 FUEL TANK 21 INTAKE AIR TEMPERATURE SENSOR (IATS)
5 VACUUM SOLENOID VALVE 22 B BANK IGNITION MODULE
6 ABSOLUTE PRESSURE SENSOR(S) 23 A BANK IGNITION MODULE
7 A BANK FUEL INJECTORS (FI) 24 A BANK DOWNSTREAM HEATED OXYGEN SENSOR (HO2S)
8 ENGINE SPEED SENSOR 25 A BANK UPSTREAM HEATED OXYGEN SENSOR (HO2S)
9 THROTTLE POSITION SENSOR (TPS) 26 TRANSMISSION CONTROL MODULE (TCM)
10 IGNITION COIL PACK 27 ENGINE CONTROL MODULE (ECM)
11 B BANK FUEL INJECTORS (FI) 28 INERTIA SWITCH
12 IGNITION COIL PACK 29 CAMSHAFT POSITION SENSOR (CMPS)
13 B BANK IDLE AIR CONTROL VALVE (IACV) 30 IGNITION COIL PACKS
14 A BANK EVAPORATIVE EMISSION CONTROL VALVE (EVAPP) 31 GAS FILTER(S) (FOR MAFS)
15 B BANK EVAPORATIVE EMISSION CONTROL VALVE (EVAPP) 32 B BANK MANIFOLD ABSOLUTE PRESSURE SENSOR
16 SECONDARY AIR INJECTION PUMP (AIR PUMP)
17 CRANKSHAFT POSITION SENSOR (CKPS)

T851 / 4.04

10
 6.0 Litre V12 / ND Engine Management System

EMS COMPONENT LOCATIONS

29 7 30 30 31

6
31

18 18 13 6 31

17
31 6 20 29

T851 / 4.05

11
12
EVAPORATIVE FUEL RAIL
ROLL-OVER FLANGE
VALVE

INTAKE INTAKE
MANIFOLD MANIFOLD

FUEL INJ.
JET CHECK
PUMP VALVE
SURGE IDLE AIR IDLE AIR
POT CONTROL CONTROL
FUEL
VALVE VALVE
PRES.
REG.

FUEL TANK FUEL PUMP FUEL PUMP

1 2
V12 / ND EVAPORATIVE EMISSION CONTROL SYSTEM

FILTER

PRESSURE
CONTROL VALVE
(ROCHESTER
VALVE) EVAPORATIVE
VALVES
(NORMALLY CLOSED)
6.0 Litre V12 / ND Engine Management System

ENGINE ENGINE LOAD

EVAPORATIVE CONTROL
CANISTER MODULE
VENT ENGINE SPEED
Fuel Delivery and Evaporative Emission Control

T851 / 4.06
 6.0 Litre V12 / ND Engine Management System

Fuel Delivery
Fuel Tank FUEL TANK ARRANGEMENT
The fuel tank incorporates two fuel pumps and
the necessary plumbing for fuel supply and
return. The tank uses baffle plates to reduce
fuel surge and a surge pot to ensure that a con-
stant supply of fuel is available for the pumps.
Each pump is located by a rubber mount and
clamp attached to the surge pot. The tank inte-
rior piping incorporates a jet pump and a check
valve in the fuel return line. Returning fuel
flows through the jet pump, which draws addi-
tional cool fuel from the tank for supply to the
surge pot. This supplemented return flow
ensures that the surge pot remains full of fuel. T851/4.07
The return check valve prevents reverse flow
through the fuel return line.

Access to the tank interior is through the

evaporative flange at the top of the tank.

Fuel Pumps FUEL PUMP WITH CROSS-SECTION

Two fuel pump assemblies are used for two- TOP VIEW
stage fuel delivery. The pump units consist of
a turbine driven by a DC motor, a check valve
and an inlet filter. The fuel output from the
turbine pump provides a cooling flow around
the motor before being discharged through
the outlet check valve. The check valve pre- ELECTRICAL
OUTLET
vents reverse flow when the engine is CONNECTOR
switched off.

Fuel pump specifications

Nominal pump delivery:
26.45 gallons per hour at 43.5 psi (3 bar)
Current draw:
7 amps at 13.2V (3 bar)

In-line Fuel Filter

A replaceable in-line fuel filter is located in the
supply line above the rear axle on the left side.

NOTES

T851 / 4.08, 4.09

13
6.0 Litre V12 / ND Engine Management System

Fuel Delivery (continued)

Twin Fuel Pump Control
When the ignition is switched on (position II), the ECM initially switches on fuel pump 2, after a delay
of 0.1 second. If the ignition switch remains in position II without moving the key to crank (position
III), the ECM will switch off pump 2 after a maximum of 3 seconds (1995 MY) or 0.8 seconds (1996
MY). When the ignition switch is moved to crank (position III), fuel pump 2 is switched off and fuel
pump 1 is activated. Fuel pump 1 operates continuously while the engine is running. The ECM acti-
vates pump 2 at higher engine speeds to provide increased fuel flow during high engine demand. Fuel
pump 2 is controlled from a predetermined engine speed and load strategy.

Both fuel pumps are switched directly by the ECM via fuel pump relays.

TWIN FUEL PUMP CONTROL

GROUND POWER FUEL

FUEL PUMP 1 FUEL PUMP
CONTROL RELAY 1 PUMP 1

ENGINE SPEED GROUND POWER

FUEL PUMP 2 FUEL PUMP FUEL
CONTROL RELAY 2 PUMP 2
ENGINE LOAD

ENGINE CONTROL MODULE

T851 / 4.10

NOTE: In the event of a vehicle collision, the inertia switch will switch off all ignition powered circuits,
including EMS power and fuel pump relay power. This action will switch off the fuel pumps and pre-
vent fuel flow.

Fuel pump monitoring for OBD II

The drive voltage to the fuel pump relays is continuously monitored. If the voltage is not within the
expected limits, a DTC will be flagged. The fault must occur on two consecutive trips to activate the
CHECK ENGINE MIL. Refer to DTC Summary: Group 10, page 62.

NOTES

14
 6.0 Litre V12 / ND Engine Management System

Fuel Pressure Regulator FUEL PRESSURE REGULATOR

Fuel is pumped to the fuel rail and injectors,
where fuel pressure is controlled by the fuel
pressure regulator. The pressure regulator is
a carry-over component from the Lucas /
Marelli 6.0L V12 system. Excess fuel, above
the engine requirement, is returned to the fuel
tank. The pressure regulator spring chamber
above the diaphragm is referenced to intake
manifold vacuum. The differential pressure
across the fuel injector nozzles is therefore
maintained constant at 44 psi (3.0 bar) and the
quantity of fuel injected for a given injector
pulse duration is also constant. Fuel pressure
measured on a test gauge will vary between
32 psi (2.3 bar) at overrun to 44 psi (3.0 bar) at T851 / 4.11
full load to compensate for intake manifold
absolute pressure.

The fuel pressure regulator is located as close

as possible to the fuel rail so that good
dynamic control of fuel pressure is achieved.
This design provides the same pressure
across each injector, and delivers an equal
quantity of fuel to each of the twelve cylinders.

NOTES

15
6.0 Litre V12 / ND Engine Management System

Fuel Delivery (continued)

Fuel Injectors
The fuel injectors are needle valve type injectors that are unique to the V12 / ND system. The
injectors are connected directly to the fuel rail and retained by clips and ‘O’ ring seals.

FUEL INJECTOR CROSS SECTION FUEL INJECTOR LOCATION

NEEDLE VALVE CORE

COIL FILTER

INJECTOR COIL RESISTANCE (NOMINAL): 14.5 OHMS

T851 / 4.13 T851 / 4.12

FUEL INJECTOR CHARACTERISTIC

The injector drive signal is a single pulse. The
pulse width is modulated to control the injector
INJECTOR PULSE: 2000 RPM, NO LOAD (REFERENCED TO GROUND) pulse duration.
40
Fuel injector monitoring for OBD II
30 The drive signal to each pair of injectors is com-
pared to an expected voltage value. If the drive
value is not correct for a specific number of injec-
VOLTAGE

20
tor pulses, an injector fault DTC will be flagged.
10 The fault must occur on two consecutive trips to
activate the CHECK ENGINE MIL. Refer to DTC
0 Summary: Group 11, page 58.

10
0 2 4 6 8 10
MS
T851 / 4.14

NOTES

16
 6.0 Litre V12 / ND Engine Management System

Evaporative Emission Control

The fuel tank can be filled to approximately EVAPORATIVE EMISSION CONTROL SYSTEM
90% of its capacity. The additional 10% of
volume allows for expansion of the fuel with-
out escape to the atmosphere.
A BANK B BANK

When the engine is switched off, the fuel tank

pressure is maintained at a positive pressure
of 1.0 – 1.33 psi by the pressure control valve.
Pressure above 1.33 psi is released by the
valve to the evaporative canister.
IDLE AIR
CONTROL VALVES VACUUM
When the engine is running, manifold vacuum
acts on the pressure control valve, which EVAPORATIVE
opens the vent line from the fuel tank to the CONTROL
VALVES
evaporative canister. Air enters the canister
and flows to the tank to replace the fuel deliv-
ered to the engine and maintain atmospheric
pressure in the tank.
EVAPORATIVE
CANISTER
If the pressure control valve fails, the fuel
PRESSURE
tank cap will vent the fuel tank pressure at CONTROL
2.0 – 2.5 psi. VALVE

Canister Purge EVAPORATIVE FLANGE

When canister purge is enabled by the ECM,

the ECM meters purge flow to the idle air con-
trol valves through the normally closed evapo-
rative emission control (purge) valves (EVAPP).
Purge flow depends on engine speed and
load, idle switch status (open / closed), and the
status of certain diagnostic functions.

NOTES

T851 / 4.15

17
6.0 Litre V12 / ND Engine Management System

Evaporative Emission Control (continued)

EVAPP DRIVE SIGNALS AT ECM

Canister Purge (continued)
NO LOAD The EVAPP drive signal is a square wave that is
20
both pulse width an frequency modulated.
15
EVAP monitoring for OBD II
The EVAP system is tested during the first long
VOLTAGE

10
hot idle period after each engine start. The ECM
5
activates each EVAPP (purge valve) individually
and checks for changes in short term fuel adap-
0
tation in each bank as well as idle air control valve
feedback and engine speed. If the monitored
5 values do not change a predetermined amount,
0 20 40 60 80 100 a DTC is flagged. The EVAPP drive signals are
MS also monitored during purge flow. If the drive
LIGHT LOAD signal state does not match the ECM command
20
for a preset number of ON / OFF cycles, a DTC is
flagged. The fault must occur on two consecu-
15
tive trips to activate the CHECK ENGINE MIL.
Refer to DTC Summary: Group 17, page 61.
VOLTAGE

10

NOTE: A and B bank EVAPP electrical connec-

5
tions and hose routing must be correct or rough
0
idle will occur and / or a DTC will be flagged.

5 NOTES
0 20 40 60 80 100
MS

MODERATE LOAD
20

15
VOLTAGE

10

5
0 20 40 60 80 100
MS

TORQUE CONVERTER STALL

20

15
VOLTAGE

10

5
0 20 40 60 80 100
MS
T851 / 4.16 A – D

18
 6.0 Litre V12 / ND Engine Management System

Evaporative Emission Control Valves (EVAPP)

The evaporative emission control (purge) valves are normally closed. These valves are visually similar
to the normally open valves used in the V12 Lucas / Marelli EMS. The amount of valve opening (and
canister purge flow) is determined by the ECM drive signals allowing the ECM to accurately control
purge flow for the prevailing engine operating conditions. The EVAPP valves are mounted below the
left headlight module.

CAUTION: Do not interchange the EVAPP valves between the V12 / ND EMS and the V12
Lucas / Marelli EMS. Before installation, verify that the correct part number is stamped on
the valve.

EVAPORATIVE EMISSION CONTROL VALVE EVAPORATIVE EMISSION CONTROL VALVES LOCATION

T851 / 4.17 T851 / 4.18

Evaporative Canister EVAPORATIVE CANISTER

The new reshaped evaporative canister (char-
coal canister) is identical in operation to previ-
ous canisters. The new canister contains fil-
ters to prevent charcoal particle leakage. The
canister is located under the vehicle near the
intermediate mufflers.

NOTES

T851 / 4.19

19
6.0 Litre V12 / ND Engine Management System

Fuel Injection
Fuel metering is obtained by controlling the injector pulse during each engine cycle (two crankshaft
rotations). The pulse duration is varied by the engine control module (ECM) according to several sensor
inputs. The sensed control inputs form two groups — primary and secondary. Primary control inputs are
manifold absolute pressure (engine load) and engine speed; secondary control inputs consist of engine
coolant temperature, cranking signal, throttle movement and position, exhaust oxygen content and
vehicle elevation. The injector pulse is then corrected for actual battery voltage. Depending on engine
operating conditions, fuel injectors are pulsed semisequentially in pairs, in a group (A bank, B bank), or all
12 simultaneously. Semisequentially means twice per engine cycle (once per engine revolution) in the
engine firing order.

Fuel injector pairing is as follows: 1A / 5A; 2A / 4A; 3A / 6A; 1B / 4B; 2B / 6B; 3B / 5B.

Fuel metering strategies are held in memory (EPROM) in the ECM and form an engine load versus
engine speed matrix. Digital numbers representing injector pulse duration in milliseconds fill each site
and cover the entire engine load and speed range. During most engine operating conditions, fuel
metering correction is applied to A bank and B bank independently. In some instances, fuel metering
correction is applied to all twelve cylinders simultaneously.

The ECM times the injection pulse using the crankshaft position sensor (CKPS) input that occurs
once per engine revolution, and the engine speed (RPM) sensor input that occurs 12 times per
engine revolution. The ECM distributes (sequences) the paired injection pulses in the engine firing
order using the camshaft position sensor (CMPS) input that occurs once per engine cycle as cylin-
der A1 approaches TDC on the compression stroke. Refer to the RPM Sensor, CKPS and CMPS
descriptions on pages 26 – 29.

Additional fuel injection controls are used for overrun fuel cutoff, engine overspeed prevention, and fuel
cutoff during wide-open-throttle cranking.

NOTES

20
 6.0 Litre V12 / ND Engine Management System

Fuel Injection Primary Control FUEL INJECTION PRIMARY AND SECONDARY CONTROL
Fuel metering is controlled primarily as a func-
tion of engine load and speed. Engine load is
ENGINE CONTROL MODULE
sensed by the intake manifold absolute pres-
sure sensors (MAPS) (one A bank, one B
bank) connected to the rear of the engine air FUEL INJECTION
ENGINE LOAD STRATEGY
intake manifolds. Engine speed is sensed by
the engine speed sensor (RPM Sensor) lo-
ENGINE SPEED PRIMARY INJECTOR
cated at the rear of the engine vee. The ECM PULSE DURATION
processes the input from the two MAPS and
the RPM Sensor to access pulse duration
CLOSED
from the fuel metering strategy. LOOP EXHAUST OXYGEN
AIR / FUEL CONTENT
RATIO

NOTES
ENABLE / CANCEL

ENGINE CRANKING CORRECTION

ENGINE COOLANT FACTORS
TEMP.
ACCELERATION AFTER-START ENGINE COOLANT TEMP.
ENRICHMENT
FULL LOAD TIME AFTER START

DECELERATION
WARM-UP
STRATEGY ENGINE COOLANT TEMP.
VEHICLE ELEVATION

INTAKE AIR TEMP.

BATTERY
VOLTAGE BATTERY
CORRECTION VOLTAGE

INJECTOR
PULSE DURATION

ENGINE OPERATING
CONDITION
ENGINE SPEED SENSOR SEMISEQUENTIAL
CRANKSHAFT POSITION OR GROUPED
SENSOR FUEL INJECTION
CAMSHAFT POSITION
SENSOR

FUEL INJECTOR PAIRS

T851 / 4.20

21
6.0 Litre V12 / ND Engine Management System

Fuel Injection (continued)

Fuel Injection Secondary Control
Secondary fuel metering control adjusts for engine coolant temperature, cranking signal, throttle move-
ment and position, exhaust oxygen content, vehicle elevation, intake air temperature, battery voltage
and the number of engine revolutions after engine starting.

Cranking and engine start enrichment

The ECM provides fuel metering enrichment for engine starts by increasing the injector pulse duration
and “grouping” fuel injection. When the ECM receives a “crank” signal (parallel circuit from the body
processor module output to the starter relay coil) plus an engine speed signal, injector pulse duration
is increased and grouped injection takes place four times per engine cycle until the engine starts. In
addition, there is a single simultaneous pulse of all 12 injectors upon initial cranking.

Crank signal monitoring for OBD II

If the engine is running with a continuous crank signal or started without a crank signal, a DTC will be
flagged. The fault must occur on two consecutive trips to activate the CHECK ENGINE MIL. Refer
to DTC Summary: Group 8, page 59.

After-start enrichment
After engine start, injector pulsing occurs in pairs semisequentially. The injector pulse duration, and the
rate at which the enrichment is decreased back to the warm-up phase, are dependent upon engine
coolant temperature, measured by the engine coolant temperature sensor (ECTS), and the time after
engine starting.

Warm-up
The programmed warm-up enrichment provides extra fuel during engine warm-up based on the en-
gine temperature, measured by the coolant temperature sensor (ECTS). The warm-up phase is applied
when the coolant temperature is below normal operating temperature.

Acceleration enrichment
When the ECM senses that the throttle is opening (throttle position sensor (TPS) input), the injector
pulse duration is lengthened by an amount dependent upon the rate at which the throttle is opened,
and on engine coolant temperature.

Full load enrichment

If the ECM senses a full throttle input from the throttle position sensor (TPS) and the manifold abso-
lute pressure sensors (MAPS), full load enrichment is applied and momentary simultaneous (all 12
injectors) injection occurs. Closed loop operation is temporarily canceled.

Deceleration leaning
When the ECM senses that the throttle is closing (TPS input), the injector pulse duration is shortened
dependent on the rate at which the throttle closed, preventing a momentary rich condition.

Closed loop fuel metering (Short term fuel trim)

In order to significantly reduce exhaust emission, the exhaust system incorporates two primary and two
secondary 3-way catalytic converters that oxidize CO and HC, and reduce NOx. These converters op-
erate efficiently only if engine combustion is as complete as possible. A closed loop system between
fuel injection, ECM control, and exhaust oxygen content feedback is used to maintain an air / fuel
ratio as close to optimum (stoichiometric) as possible. In response to oxygen sensor voltage, the ECM
continuously drives the air / fuel ratio rich-lean-rich by adding to, or subtracting from the baseline injector
pulse duration. Refer to Heated Oxygen Sensors, pages 34 – 35.

NOTES

22
 6.0 Litre V12 / ND Engine Management System

Closed loop fuel metering is canceled during the following engine operation conditions:
• engine starting
• air injection operation
• full load
• fuel metering cutoff
• certain fault conditions

Vehicle elevation
At high elevations, the fuel metering pulse is corrected using the input from the high altitude correc-
tion sensor (HACS) within the ECM. Refer to High Altitude Correction, page 5.

Intake air temperature

At low intake air temperature, the fuel metering pulse is increased to compensate for the increased
intake air density.

Battery voltage correction

Because the time to achieve full lift of the injector pintle decreases as voltage increases, the amount
of fuel delivered by the injector for a given pulse duration is dependent upon the injector operating
voltage. The ECM is programmed with a voltage correction strategy. The supply voltage is monitored
by a software routine and the correction applied to the pulse duration.

Additional Fuel Injection Controls

Overrun fuel cutoff
In order to improve fuel economy and aid in controlling exhaust emission, the ECM cancels fuel injection
during engine overrun conditions. The ECM determines overrun conditions from inputs received from the
throttle position sensor (TPS), engine speed (RPM) sensor and engine coolant temperature sensor (ECTS).

Engine overspeed control

An engine overspeed control function limits the maximum engine speed by canceling fuel injection, initially
at 6100 rpm. If maximum engine speed is maintained, fuel injection cancellation is reduced to 6000 rpm.

Wide-open-throttle during cranking

If the ECM senses that the throttle is wide open (throttle position sensor (TPS) input) during cranking,
fuel injection is canceled to help clear a flooded engine.

Fuel metering adaption (Long term fuel trim)

Long term fuel trim allows for minor engine mechanical variability and engine aging. The ECM con-
tains adaptive idle fuel metering software that automatically makes a baseline correction to the idle
fuel metering strategy using long term information from the oxygen sensors. The adaptive values
are held in memory and will be retained as long as the vehicle battery is connected. If the battery
is disconnected, the adaptive values will be lost. The ECM will relearn the values during the next
driving cycle (if conditions permit).

Long term fuel trim monitoring for OBD II

Fuel metering is monitored for adapted values at the rich / lean limit. If the value is beyond the limit(s),
a DTC is flagged. The fault must occur on two consecutive trips to activate the CHECK ENGINE MIL.
Refer to DTC Summary: Group 6, page 57.

NOTES

23
6.0 Litre V12 / ND Engine Management System

EMS Main Sensing Components: Engine Load

Manifold Absolute Pressure Sensors (MAPS)
MANIFOLD ABSOLUTE PRESSURE SENSOR WITH CROSS-SECTION
A manifold absolute pressure sensor (MAPS) is
connected to each intake manifold (A bank and
B bank). The MAPS incorporates a pressure
sensor capsule connected to a resistive ele-
ment. Manifold absolute pressure changes
(throttle valve opening / closing) act on the pres-
sure capsule, which in turn acts on the resistive
element to alter resistance. The MAPS is sup-
plied with 5 volts from the ECM and outputs a
voltage to the ECM that is directly proportional
to manifold absolute pressure. The ECM uses
the A and B bank MAPS inputs independently
(not averaged) to control the respective bank in
an aim for optimum combustion. Some aver-
PRESSURE SENSING
CAPSULE aged values (A bank and B bank) are used
during OBD monitoring.

The MAPS are mounted on the rear of each

intake manifold and connect to the manifold by a
hose through a gas filter. The gas filter prevents
MAPS contamination from crankcase vapors.

MANIFOLD ABSOLUTE PRESSURE SENSOR

LOCATION
MAPS

ELECTRICAL
CONNECTOR

INTAKE MANIFOLD
(VIA GAS FILTER)

T851 / 4.22A & B

GAS FILTER CROSS-SECTION GAS FILTER T851 / 4.21

NOTES

INTAKE
MAPS MANIFOLD

T851 / 4.24

24
 6.0 Litre V12 / ND Engine Management System

Manifold Absolute Pressure (MAP) MAPS CHARACTERISTIC

versus Gauge Vacuum (approximate)
MAP Vacuum
(in hg = inches of mercury) VOLTAGE

30 in hg 0 in hg 3.6
29 in hg 1 in hg
28 in hg 2 in hg
27 in hg 3 in hg 2.4
26 in hg 4 in hg
25 in hg 5 in hg
24 in hg 6 in hg 1.2
23 in hg 7 in hg
22 in hg 8 in hg
0 PRESSURE
21 in hg 9 in hg
BAR 0 0.2 Bar 0.6 Bar 1 Bar
20 in hg 10 in hg
PSI 0 2.9 psi 8.7 psi 14.5 psi
19 in hg 11 in hg
18 in hg 12 in hg MAP 0 6 in hg 18 in hg 30 in hg

17 in hg 13 in hg GAUGE 30 in hg 24 in hg 12 in hg 0 in hg
VACUUM
16 in hg 14 in hg
15 in hg 15 in hg
T851 / 4.24
14 in hg 16 in hg
13 in hg 17 in hg
12 in hg 18 in hg
11 in hg 19 in hg
10 in hg 20 in hg

MAPS monitoring for OBD II

The range of the MAPS signal to the ECM is checked for values outside of the normal limits. If the
signal stays high or low continuously (open / short circuit), a DTC is flagged and the CHECK ENGINE
MIL is activated immediately. The MAPS signal is also monitored during acceleration after an idle
period. If the signal does not change as expected, a DTC will be flagged. The fault must occur on two
consecutive trips to activate the CHECK ENGINE MIL. Refer to DTC Summary: Group 1, page 54.

NOTES

25
6.0 Litre V12 / ND Engine Management System

EMS Main Sensing Components: Engine Speed and Position

ELECTROMAGNETIC SENSOR PULSES: ONE ENGINE CYCLE

Three electromagnetic sensors are installed on the
engine: the engine speed sensor (RPM Sensor),
the crankshaft position sensor (CKPS), and the
TDC camshaft position sensor (CMPS).

CRANKSHAFT POSITION SENSOR: 26˚ BTDC

The ECM uses the engine speed sensor input to
@ 800 rpm
+ determine engine speed and for individual cylin-
4V min
der identification. The ECM uses the camshaft
0V position sensor input for compression stroke
identification (A bank). All three inputs are re-
– quired semisequential fuel injection.

The illustration at left shows all of the pulses pro-

vided to the ECM during one engine cycle (two
CAMSHAFT POSITION SENSOR: 48˚ BTDC @ 800 rpm engine revolutions).
+
1V min
NOTES
0V

ENGINE SPEED SENSOR: 10˚ BTDC @ 800 rpm

+
2V min
0V

ENGINE CYCLE

T851 / 4.25

26
 6.0 Litre V12 / ND Engine Management System

Engine Speed Sensor (RPM Sensor) ENGINE SPEED SENSOR LOCATION

The engine speed sensor (RPM Sensor) is
located behind the flywheel at the rear of the
engine vee. The sensor is a variable reluc-
tance device that provides a pulse to the ECM
at 30° intervals. A disc, mounted to the crank-
shaft, has twelve “spokes” that pass the RPM
Sensor. The spokes are spaced 30˚ (crank-
shaft angle) apart on the disc. The ECM uses
the RPM Sensor pulses for engine speed
information. In addition, the ECM uses the
pulse, in conjunction with the CKPS and
CMPS pulses for cylinder synchronization.

The RPM Sensor provides twelve pulses per

engine revolution starting at cylinder A1 at 10° T851 / 4.26

BTDC and thereafter at every 30° of crank-

shaft rotation.
ENGINE SPEED SENSOR CROSS-SECTION
RPM Sensor monitoring for OBD II
The RPM Sensor signal is monitored during
engine cranking (determined by the “crank-
ing” signal input to the ECM). If there is no
RPM Sensor signal while a “cranking” signal
is present, a DTC is flagged and the CHECK
ENGINE MIL is activated immediately. Refer
COIL
to DTC Summary: Group 14, page 60.

The RPM Sensor signal is also compared to

the crankshaft position sensor input when the
engine is running. If the expected number of
RPM Sensor pulses are not received, a DTC is
flagged and the CHECK ENGINE MIL is acti- T851 / 4.27

vated immediately.

ENGINE SPEED SENSOR CHARACTERISTIC

NOTES

OUTPUT
VOLTAGE 0V

T851 / 4.28

27
6.0 Litre V12 / ND Engine Management System

EMS Main Sensing Components: Engine Speed and Position (continued)

CRANKSHAFT SENSOR LOCATION

Crankshaft Position Sensor (CKPS)
The crankshaft position sensor (CKPS) is located
at the bottom of the crankshaft front pulley. The
sensor is a variable reluctance device that pro-
vides a pulse to the ECM once each engine
revolution. A disc, mounted to crankshaft
damper has one tooth that passes the CKPS.
The ECM uses the CKPS pulse for semisequential
fuel injection in conjunction with the RPM Sensor
and CMPS pulses. In addition, the ECM uses the
pulse, in conjunction with the RPM Sensor
pulses for grouped (bank) fuel injection and igni-
tion timing.

The CKPS provides a pulse once per engine revo-

T851 / 4.29 lution synchronized to cylinder A1 at 26° BTDC.

CKPS monitoring for OBD II

CRANKSHAFT SENSOR CROSS-SECTION The CKPS signal is compared to the RPM Sensor
signal. If there are 36 RPM Sensor pulses and no
CKPS pulse, a DTC is flagged and the CHECK
ENGINE MIL is activated immediately. Refer to
DTC Summary: Group 14, page 60.

The three sensors (RPM Sensor, CKPS, and

CMPS) are also continuously compared to one
COIL another when the engine is running. If an unex-
pected signal is detected, a DTC is flagged and the
CHECK ENGINE MIL is activated immediately.

NOTES

T851 / 4.30

CRANKSHAFT SENSOR CHARACTERISTIC

OUTPUT
VOLTAGE 0V

T851 / 4.31

28
 6.0 Litre V12 / ND Engine Management System

Camshaft Position Sensor (CMPS) CAMSHAFT SENSOR LOCATION

The camshaft position sensor (CMPS) is
located on the A bank camshaft cover at the
front of the engine. The sensor is a variable
reluctance device that provides a pulse to the
ECM once each engine cycle (two engine
revolutions). A single peg on the A bank cam-
shaft passes the CMPS once per camshaft
revolution (two engine revolutions). The ECM
uses the CMPS pulse in conjunction with the
RPM Sensor and CKPS pulses for timing
semisequential fuel injection in the engine fir-
ing order.

The CMPS provides one pulse per engine CAMSHAFT PEG

cycle (two engine revolutions) synchronized to
cylinder A1 at 48° BTDC on the compression
stroke.

CMPS monitoring for OBD II

The CMPS signal is compared to the CKPS T851 / 4.32A & B
signal. If there are 5 CKPS pulses and no
CMPS pulse, a DTC is flagged and the CHECK
ENGINE MIL is activated immediately. Refer CAMSHAFT SENSOR CROSS-SECTION
to DTC Summary: Group 14, page 60.

NOTES

‘O’ RING

COIL T851 / 4.33

CAMSHAFT SENSOR CHARACTERISTIC

OUTPUT
VOLTAGE 0V

T851 / 4.34

29
6.0 Litre V12 / ND Engine Management System

EMS Main Sensing Components: Temperature

INTAKE AIR TEMPERATURE SENSOR

Intake Air Temperature Sensor (IATS)
The intake air temperature sensor (IATS) is a
negative temperature coefficient (NTC) ther-
mistor identical to the sensor used in V12 Lucas
/ Marelli EMS. Intake air temperature is deter-
mined by the ECM by a change in resistance
within the sensor. The ECM applies 5 volts to
the sensor and monitors the voltage across the
pins to detect the varying resistance.

Intake air temperature sensor –

T851 / 4.35 temperature versus resistance:
Intake air temperature Resistance
°F °C (kilo ohms)
INTAKE AIR TEMPERATURE SENSOR LOCATION
68 20 2.50
176 80 0.325
212 100 0.19

IATS monitoring for OBD II

The IATS range is checked for values outside the
normal limits while the engine is running. If the
signal is out of the normal range for more than
25.6 seconds, a DTC will be flagged. The fault
must occur on two consecutive trips to activate
the CHECK ENGINE MIL.

If the IATS signal is high or low (open / short cir-

cuit) continuously, a DTC is flagged and the
T851 / 4.36
CHECK ENGINE MIL is activated immediately.
Refer to DTC Summary: Group 2, page 54.

NOTES

30
 6.0 Litre V12 / ND Engine Management System

Engine Coolant Temperature Sensor (ECTS)

The engine coolant temperature sensor (ECTS), located on the B bank thermostat housing, is a negative
temperature coefficient (NTC) thermistor. Engine coolant temperature is determined by the ECM by
a change in resistance within the sensor. The ECM applies 5 volts to the sensor and monitors the volt-
age across the pins to detect the varying resistance.

Coolant temperature sensor – ENGINE COOLANT TEMPERATURE SENSOR WITH CROSS-SECTION

temperature versus resistance:
Coolant temperature Resistance
°F °C (kilo ohms)
68 20 2.45
176 80 0.318
230 110 0.1417

Coolant temperature sensor –

temperature versus voltage:
Coolant temperature Voltage
°F °C
THERMISTOR
-13 -25 4.43
20 -7 3.8
40 4 3.18
60 16 2.55
86 29 1.93
112 45 1.31
158 70 0.68
247 119 0.2
ELECTRICAL
ECTS monitoring for OBD II CONNECTOR
Two test are performed to check the ECTS: T851 / 4.37A & B

1 The ECTS signal is checked for values

outside the normal range. If there is a fault,
a DTC is flagged and the CHECK ENGINE ENGINE COOLANT TEMPERATURE SENSOR
MIL is activated immediately.
2 A “time to warm-up” test checks that the
sensor responds to a rise in coolant tem-
perature. If there is a fault, a DTC is
flagged. The fault must occur on two con-
secutive trips to activate the CHECK
ENGINE MIL.
Refer to DTC Summary: Group 3, pages 54
and 55).

NOTES

T851 / 4.38

31
6.0 Litre V12 / ND Engine Management System

EMS Main Sensing Components: Throttle Position

THROTTLE POSITION SENSOR WITH CROSS-SECTION

Throttle Position Sensor (TPS)
The throttle position sensor (TPS) is an adjustable
single-track potentiometer connected to the
spindle of the throttle turntable. The TPS incorpo-
rates an idle switch that is closed when the
throttle is closed.

The ECM applies 5 volts to the sensor and moni-

tors the voltage across the pins to determine
throttle position: low voltage / closed throttle, high
voltage / opened throttle. At full throttle, the volt-
age signal to the ECM is approximately 3.4 volts.
The idle switch provides a ground input to the
ECM when the throttle is closed.
DRIVE PLATE ELECTRICAL
CONNECTOR
After installation of a TPS, initial adjustment must
be performed using PDU.

NOTES

RETURN
SPRING

WIPER RESISTIVE
CONTACT TRACK
T851 / 4.39A & B

THROTTLE POSITION SENSOR LOCATION

T851 / 4.40

32
 6.0 Litre V12 / ND Engine Management System

TPS monitoring for OBD II THROTTLE POSITION SENSOR CHARACTERISTIC

Two test are performed to check the TPS:
1 The TPS signal is checked for values out
side the normal range. If there is a fault, a IDLE CLOSE OPEN
DTC is flagged and the CHECK ENGINE SWITCH
MIL is activated immediately.
SWITCHING
OUTPUT
2 If, during steady driving, the sensor voltage
does not change in comparison to changing
MAP and RPM signals, a fault is flagged. 5 +
– 0.15V

OUTPUT VOLTAGE
The fault must occur on two consecutive
trips to activate the CHECK ENGINE MIL.
Refer to DTC Summary: Group 4, page 55.
LINEAR
OUTPUT
Idle switch monitoring for OBD II
The idle switch is checked by the ECM during
0
deceleration and acceleration. If the ECM THROTTLE TURNTABLE ROTATING ANGLE
0˚ 125˚
does not receive an idle switch change of
state during five consecutive deceleration/ac-
T851 / 4.41
celeration cycles, a DTC is flagged. The fault
must occur on two consecutive trips to acti-
vate the CHECK ENGINE MIL. Refer to DTC
Summary: Group 21, page 62.

Sensor power supply monitoring for OBD II

The supply voltage to the MAPS, IATS, ECTS
and TPS is monitored for high or low voltage.
If the voltage is high or low, a DTC is flagged.
The fault must occur on two consecutive trips
to activate the CHECK ENGINE MIL. Refer to
DTC Summary: Group 12, page 58.

NOTE: If the A and B bank MAP sensors and

the TPS have failed at the same time, a sensor
power supply DTC will be flagged. The fault
must occur on two consecutive trips to acti-
vate the CHECK ENGINE MIL.

NOTES

33
6.0 Litre V12 / ND Engine Management System

EMS Main Sensing Components: Exhaust Gas Oxygen Content

HEATED OXYGEN SENSOR WITH CROSS-SECTION

Heated Oxygen Sensors (HO2S)
The V12 / ND EMS uses four heated oxygen
sensors (HO2S), one upstream and one down-
stream of the primary catalyst on each cylinder
bank exhaust pipe.

The sensors used in the V12 / ND EMS are simi-

lar in characteristic to the HO2S used in the V12
Lucas / Marelli EMS. These produces voltage
by conducting oxygen ions at approximate tem-
peratures above 572°F (300°C). In order to
reduce the amount of exhaust gas and resulting
emission needed to bring the sensor up to
working temperature, an internal electric heater
is used. The heaters are controlled by the ECM.
At engine speeds above approximately 3000
PROTECTIVE TUBE
rpm, the ECM switches off the heaters. The tip
portion of the sensor’s ceramic element is in
contact with the exhaust gas. The remaining
portion of the ceramic element is in contact with
ambient air via a filter through the sensor body.
HEATER (10 – 20 Ω @ 68°F [20°C])
ZiO2 - CERAMIC Four oxygen sensors are installed on the exhaust
SENSOR TIP T851 / 4.43A & B system, one upstream and one downstream of
the primary catalysts for each cylinder bank. The
two upstream sensors are used by the ECM for
HEATED OXYGEN SENSORS LOCATION closed loop fuel metering correction. The down-
stream sensors for used for OBD catalyst
monitoring. Refer to Closed Loop Fuel Metering,
pages 24 – 25.

The construction of the upstream and down-

stream sensor harnesses are different so that
they cannot be interchanged. However, there
are no orientation “rules”. If the battery is discon-
nected, the ECM will relearn adaptive values
during the next driving cycle when new sensors
are installed, or if sensors are switched side-
to-side.

NOTES

T851 / 4.42

34
 6.0 Litre V12 / ND Engine Management System

The sensor voltage output swings between HEATED OXYGEN SENSOR CHARACTERISTIC
approximately 800 millivolts and approximately
200 millivolts depending on the oxygen level
differential between ambient air and exhaust
gas on either side of the ceramic element. 800mV
When the air / fuel ratio is richer than opti-
mum, the voltage output is high; when the
air / fuel ratio is leaner than optimum, the out-

OUTPUT VOLTAGE
put voltage is low. Only a very small change
in air / fuel ratio is required to switch the oxy-
gen sensor.

HO2S monitoring for OBD II

The oxygen sensors and heater circuits are
monitored during steady driving with a fully
warmed-up engine. 200mV

The upstream and downstream sensor output

voltages are compared to a normal range and
to each other. The sensors are also tested RICHER λ = 1 LEANER
when a fuel system fault has been detected. (OPTIMUM)
T851 / 4.44
Periodically, the sensor response rates are
compared to a standard. If there is a fault, a
DTC is flagged. The fault must occur on two HEATED OXYGEN SENSOR VOLTAGE SWING TRACE – UPSTREAM
consecutive trips to activate the CHECK
ENGINE MIL. Refer to DTC Summary: Group 5, 0.86V
pages 56 – 57.
UPSTREAM OXYGEN SENSOR

700mV
NOTES

200mV

0V
T851 / 4.45

35
6.0 Litre V12 / ND Engine Management System

Ignition Control

IGNITION TIMING STRATEGY (TYPICAL)

Ignition Timing and Spark Distribution
Ignition timing and spark distribution are con-
IGNITION ANGLE trolled by the engine control module (ECM)
according to sensor inputs. As with fuel injection,
the sensed control inputs form two groups: pri-
mary and secondary. Primary control inputs are
intake manifold absolute pressure (engine load)
and engine speed; secondary control inputs con-
sist of engine coolant temperature, intake air
temperature, throttle movement and position,
and transmission shift status.

Ignition timing strategies are held in memory

LOA
D E SP
EE D (EPROM) in the ECM and form an engine load
IN
ENG versus engine speed matrix. Digital numbers
representing ignition timing values fill each site.
T851 / 4.46 The resulting ignition timing values cover the
entire engine load and speed range. Ignition tim-
ing is then calculated from the ignition timing
IGNITION PRIMARY AND SECONDARY CONTROL strategy according to secondary input correction
factors.

Spark distribution, in the engine firing order, is

ENGINE CONTROL MODULE
ECM controlled. The spark plugs are fired in pairs
(each pair 360 degrees apart in the engine cycle)
IGNITION TIMING so that the cylinder on the exhaust stroke re-
ENGINE SPEED STRATEGY
ceives a “wasted” spark. The ECM determines
spark synchronization based on the input pulses
ENGINE LOAD PRIMARY
IGNITION TIMING from the engine speed sensor (RPM Sensor) and
the crankshaft position sensor (CKPS). Refer to
the sensor descriptions, pages 27 – 28.
ENGINE CRANKING
Engine Firing Order
ENGINE COOLANT TEMP.
A1 - B6 - A5 - B2 - A3 - B4 - A6 - B1 - A2 - B5 - A4 - B3
INTAKE AIR TEMP.
CORRECTION
THROTTLE MOVEMENT
FACTORS Ignition Primary Control
IDLE
Ignition timing is controlled primarily as a func-
TRANSMISSION SHIFT
tion of engine load and speed. Engine load is
A/C COMPRESSOR
OPERATION sensed by the intake manifold absolute pres-
sure sensors (MAPS) (one A bank, one B bank)
BATTERY connected to the rear of the engine air intake
VOLTAGE
manifolds. Engine speed is sensed by the
engine speed sensor (RPM Sensor) located at
ENGINE SPEED SENSOR the rear of the engine vee. The ECM processes
IGNITION TIMING AND the inputs from the MAPS and the RPM sensor
SYNCHRONIZATION and accesses ignition timing from the ignition
CRANKSHAFT POSITION
SENSOR timing strategy.

NOTES

IGNITION COILS

T851 / 4.47

36
 6.0 Litre V12 / ND Engine Management System

Ignition Modules
Two ignition modules (amplifiers) are installed, one for each ignition coil pack. The modules receive
ignition drive signals from the ECM and, in turn control the primary current switching of the ignition coils
(three coils per ignition coil pack). Dwell control for the ignition system is performed within the ECM.

IGNITION MODULE IGNITION MODULES LOCATION

T851 / 4.49 T851 / 4.48

Ignition module monitoring for OBD II IGNITION MODULE DRIVE SIGNALS AT ECM
Each ignition module (A bank, B bank) outputs
a feedback signal to the ECM when a correct IDLE
ignition primary trigger signal has occurred. If 20

the correct number of pulses is not received

by the ECM, a DTC relating to the specific 15
bank will be flagged and the CHECK ENGINE
MIL is activated immediately. Refer to DTC
VOLTAGE

10
Summary: Group 15, page 60.
5

NOTES
0

5
0 20 40 60 80 100
MS

2000 RPM
20

15
VOLTAGE

10

5
0 20 40 60 80 100
MS
T851 / 4.50A & B

37
6.0 Litre V12 / ND Engine Management System

Ignition Control (continued)

IGNITION COIL PACK

Ignition Coil Packs
Each ignition coil pack contains three separate
ignition coils. Each coil fires two spark plugs
simultaneously (each pair 360 degrees apart
in the engine cycle) so that one spark occurs
on a compression stroke and one spark on an
exhaust stroke. The spark fired on the ex-
haust stroke (wasted spark) uses only a small
amount of the coil’s stored energy, the major-
ity going to the spark on the compression
stroke. Since the spark plugs are connected
in series, the ignition voltage of one spark
plug is negative while the other spark plug is
T851 / 4.52
positive (referenced to ground).

IGNITION COIL PACK CROSS-SECTION

HIGH TENSION
TERMINALS

PRIMARY
COIL

SECONDARY
COIL

T851 / 4.53

IGNITION COIL PACKS LOCATION NOTES

T851 / 4.51

38
 6.0 Litre V12 / ND Engine Management System

The spark plugs are paired as shown in the high-tension wiring layout.

Spark plug specification

NGK BR6EF Electrode gap: 0.026 in (0.65 mm)

HIGH TENSION WIRING LAYOUT

6B 5B 4B 3B 2B 1B

HIGH TENSION
FIRING PAIRS:

1A – 6A 4A 5A 6A 4B 5B 6B
6B – 1B
5A – 2A 3A 2A 1A 3B 2B 1B
2B – 5B
3A – 4A
4B – 3B

6A 5A 4A 3A 2A 1A

Ignition coil pack monitoring for OBD II

IGNITION COIL PRIMARY CIRCUIT CHARACTERISTIC
Ignition coil primary circuit current is monitored
by the ignition modules while the engine is IDLE
40
running. If incorrect ignition occurs, ignition
module feedback to the ECM is disrupted and 30
a DTC is flagged. Refer to Ignition Module
Monitoring for OBD II, page 37, and DTC 20
VOLTAGE

Summary: Group 15, page 60.

10

NOTES
0

10
0 20 40 60 80 100
MS

1500 RPM
40

30

20
VOLTAGE

10

10
0 20 40 60 80 100
MS

39
6.0 Litre V12 / ND Engine Management System

Ignition Control (continued)

Ignition Secondary Control
Secondary ignition timing control inputs consist of battery voltage, engine coolant temperature, intake
air temperature, throttle movement and position, and transmission shift.

Dwell control
The dwell angle and peak coil current are ECM controlled to maintain the required spark energy required
throughout the operating range of the engine while keeping dwell to a minimum to avoid overheating
of the ignition coils.

Engine coolant temperature correction

Ignition timing is corrected for engine coolant temperature by the ECM.

Intake air temperature correction

Ignition timing is corrected by the ECM for engine intake air temperature measured by the air tempera-
ture sensor mounted in the A bank air intake elbow. At higher intake air temperatures, the ignition is
retarded to prevent detonation.

Closed throttle / idle correction

Separate idle ignition strategies are used for closed throttle based on idle switch input and engine
speed. Refer to Idle Control, pages 41 – 43.

Full load correction

The ECM corrects ignition timing to compensate for full load conditions. Full load is determined by
MAPS an TPS inputs to the ECM.

Engine starting and transient correction

Ignition timing is retarded during engine starting and after rapid throttle opening to prevent detonation.

Torque-based transmission shifting

Transmission shift quality is enhanced by “torque-based shifting”. The ECM continuously provides the
transmission control module (TCM) with a pulse width modulated (PWM) signal that represents the
engine torque. This signal is generated by the ECM based on engine speed and load, plus the correc-
tion factors.

When a shift is to occur, the TCM calculates the necessary torque reduction and provides a PWM
“ignition retard request” signal to the ECM. The PWM torque reduction signal will vary between 20%
and 90% (20% equals 0° ignition retard; 90% equals 34° ignition retard). The actual amount of retard
is applied to the ignition advance angle after other corrections are applied.

Ignition retard request monitoring for OBD II

The ECM monitors the ignition retard request signal from the TCM in two ways:
1 If the signal stays at 12% for a predetermined time, a DTC will be flagged and both the CHECK
ENGINE and TRANSMISSION MILs will immediately be activated.
2 If the TCM requests ignition retard for too long, the ECM will flag a DTC and both the CHECK
ENGINE and TRANSMISSION MILs will immediately be activated.
Refer to DTC Summary: Group 24, page 62.

NOTES

40
 6.0 Litre V12 / ND Engine Management System

Idle Control
Idle speed is regulated by idle air control and IDLE AIR CONTROL VALVE WITH CROSS-SECTION
ignition timing.

The idle air control valves (IACV) are driven by

the ECM. The ECM uses inputs received
from ignition ON, the engine speed sensor
(RPM Sensor), the engine coolant temperature
sensor (ECTS) and the throttle position sensor
(TPS) as well as inputs for gear position, air
conditioning compressor operation, power
steering pump status, and road speed to con-
trol idle speed.

Idle Air Control Valves (IACV)

The throttle bodies of each bank incorporate
connections to individual idle air control valves
(IACV). The IACVs are mounted to manifolds FROM
that attach to the cylinder heads. The IACV AIR CLEANER
and manifold assemblies connect to the air
cleaners by hoses. Engine coolant is circu- SOLENOIDS
lated through the IACVs to provide an engine
temperature reference for the thermostati-
cally-controlled mechanical guard. The guard
prevents excessively high or low idle speed if SPRING

the IACV fails electrically. The throttle bodies

do not have an adjustable bleed to provide a
base idle setting. The base idle setting is con-
trolled by the IACV.

Bypass air flow is controlled by a sleeve valve

operated by a rotary solenoid containing two
TO INTAKE
coils. One coil is used to close the valve; the MANIFOLD
other coil is used to open the valve. One side SLEEVE
VALVE
of each coil receives battery voltage from an
ignition switched supply. The ECM supplies T851 / 4.57, 4.58

each coil with a pulse width modulated (PWM)

ground signal that is in “anti-phase” with the
other so that the two coils work against each IDLE AIR CONTROL VALVE LOCATION (B BANK SHOWN)
other to position the valve. When the ignition FROM
AIR
is switched OFF, a spring returns the valve to IACV CLEANER
a fixed closed position. The ECM positions
the valve for sufficient air during starting.

NOTES

IACV MANIFOLD

T851 / 4.56

41
6.0 Litre V12 / ND Engine Management System

Idle Control (continued)

IDLE AIR CONTROL VALVE OPEN / CLOSE PWM SIGNALS

Idle Air Control Valves (continued)
The PWM signals shown in the illustration are for
a valve position that is relatively open. The sig-
nals would have an opposite “duty cycle” for a
12V closed valve position.

During most operating modes, the ECM uses

OPEN 0V
COIL common control for both A and B bank IACVs;
however, individual bank corrections are made to
CLOSE 12V
COIL balance A and B bank manifold pressure and for
OBD monitoring.
0V
IACV monitoring for OBD II
The IACVs are tested during each drive cycle at
T851 / 4.59
the first long idle period at normal operating tem-
perature. Each IACV is opened individually during
which time the ECM monitors the MAP and
RPM signals for the expected response. If the
response is not as expected, a DTC is flagged.
The fault must occur on two consecutive trips to
activate the CHECK ENGINE MIL. Refer to DTC
Summary: Group 20, page 62.

ECM Idle Speed Control

The ECM controls idle speed from an idle speed strategy. This strategy is accessed when the idle
switch within the TPS closes (closed throttle). Refer to TPS, pages 32 – 33.

Closed loop idle speed control occurs at closed throttle (idle switch closed) when road speed is less
than 1.25 mph (2 kph). The programmed idle speed accounts for engine temperature and the loads
placed on the engine by the transmission (gear position N, D, etc.), air conditioning compressor clutch
operation, power steering pump pressure, vehicle elevation and battery voltage.

Target stable idle speeds: (normal operating temperature)

Park / Neutral – 700 ± 25 rpm
Drive / R, D 2, D 3 – 600 ± 25 rpm

NOTE: At road speeds above 1.25 mph (2 kph), the idle air control valves (IACVs) are opened to limit
overrun intake manifold pressure. The amount that the valves are opened is based on engine speed,
engine temperature and throttle opening.

NOTES

42
 6.0 Litre V12 / ND Engine Management System

Engine start-up
ECM idle speed control begins shortly after the engine is started, provided the throttle is closed (idle
switch closed) and the road speed is less than 1.25 mph (2 kph). The rotary solenoid valves in the
IACVs move toward close, until the target idle speed is reached.

Gear position
When the gear selector is in Park or Neutral, the engine management ECM receives a ground signal
from the linear gear position switch. The ECM then starts closing the idle air control valves in antici-
pation of the reduced engine load.

Electrical load
When the ECM receives an input from the climate control system that either the windshield heat-
ers, heated backlight or the blowers (high speed) are switched ON, the ECM compensates for this
increased engine load. The ECM drives the idle air control valves open by a programmed amount
and advances the ignition timing to compensate for the change in engine load.

Air conditioning compressor clutch operation

When the air conditioning compressor clutch is energized, the ECM drives the idle air control valves
further open and advances the ignition timing to compensate for the change in engine load.

Power steering pump pressure

POWER STEERING PRESSURE SWITCH
The ECM compensates for increased engine
load that occurs when the power steering
hydraulic pressure is high. During low speed
maneuvering and parking, a power steering
pump pressure switch closes at 475 – 625 psi
(32.75 – 43 bar) to provide the ECM with a
ground signal when the pressure is high. The
idle air control valves are driven open by a
fixed amount.

Vehicle elevation
At high elevations, the ECM compensates for
low atmospheric pressure at idle speed using
T851 / 4.60
the input from the high altitude correction sen-
sor (HACS) within the ECM. Refer to High
Altitude Correction, page 5.

Battery voltage
The ECM compensates for low battery voltage at idle by increasing the programmed idle speed by 100
rpm. The higher engine speed increases generator output.

Idle speed control adaptations

The ECM learns idle speed control adaptions at normal operating temperature in Drive and Neutral to
improve the response rate to target idle speeds. In addition, other adaptions are learned to allow lim-
ited balancing of A and B bank manifold absolute pressures. The A and B bank MAPS signals are
used by the ECM to help balance the banks through individual IACV control.

The adaptive values are held in memory and will be retained as long as the vehicle battery is connected.
If the battery is disconnected, the adaptive values will be lost. The ECM will relearn the values during
the next driving cycle.

NOTES

43
6.0 Litre V12 / ND Engine Management System

Secondary Air Injection (AIR)

Secondary air injection is employed to accelerate catalyst “light off”. “Light off” is the term used to
describe the time taken to bring the catalyst to the ideal operation temperature. Initially, after engine
start, the air / fuel mixture is rich. The exhaust from this rich mixture is still burning when it enters the
catalyst. Air is delivered to the exhaust system to prolong the catalyst burning time and raise the cata-
lyst operating temperature to the ideal level as soon as possible.

SECONDARY AIR INJECTION SYSTEM

ECM DELAY VALVE

RIGHT
INTAKE MANIFOLD

SECONDARY
AIR INJECTION
RELAY
VACUUM
SOLENOID VALVE

A BANK
AIR INJECTION RAIL

CHECK VALVE

AIR SWITCHING
VALVE
B BANK
AIR INJECTION RAIL AIR PUMP
CHECK VALVE

T851 / 4.61

The AIR system consists of a pump, AIR switching valve, solenoid vacuum valve, two check valves,
and the necessary plumbing. The ECM enables secondary air injection as necessary depending on
coolant temperature, engine speed, time after start, and OBD monitoring. Additionally, the ECM
operates the secondary air injection pump after each engine start and for a short period during normal
engine running (approximately every 30 minutes) to clear condensation from the air pipes.

NOTES

44
 6.0 Litre V12 / ND Engine Management System

Secondary Air Injection Pump (AIR Pump)

The secondary air injection pump (AIR Pump) SECONDARY AIR INJECTION PUMP CROSS-SECTION
is the same type and construction used on
the V12 Lucas / Marelli EMS. The vane-type
pump couples to an engine driven electromag-
netic clutch. The clutch is activated via a relay
that is switched by the ECM.

NOTES

T851 / 4.63

SECONDARY AIR INJECTION PUMP LOCATION

T851 / 4.62

45
6.0 Litre V12 / ND Engine Management System

Secondary Air Injection (continued)

AIR Switching Valve (ASV)
The vacuum operated AIR switching valve (ASV), located at the rear of the engine vee, controls the flow
of air injection to the exhaust system.

AIR SWITCHING VALVE CROSS-SECTION AIR SWITCHING VALVE LOCATION

AIR VACUUM
SOLENOID VALVE

SECONDARY AIR EXHAUST SYSTEM

INJECTION PUMP (VIA CHECK VALVES)

T851 / 4.65 T851 / 4.64

SECONDARY AIR INJECTION CHECK VALVE WITH CROSS-SECTION NOTES

,,,,,,,
,,,
,,,,,,,
INLET

,
,,,, ,,
,,,
,,,,,,, PERFORATED FLEXIBLE DISK
DISK VALVE

T851 / 4.66A & B

46
 6.0 Litre V12 / ND Engine Management System

AIR Vacuum Solenoid Valve (VSV) AIR VACUUM SOLENOID VALVE CROSS-SECTION
The vacuum solenoid valve (VSV), located at the AIR SWITCHING
VALVE
rear of the A bank intake manifold, switches ELECTRICAL
CONNECTOR
vacuum to the ASV. The ECM activates the
VSV one second after the AIR Pump clutch
relay, enabling the pump to reach operating
pressure before the ASV is opened. When
activated, ported vacuum is applied to the ASV, INTAKE
opening the ASV. MANIFOLD
(VIA DELAY
VALVE)
AIR monitoring for OBD II
Secondary air injection is monitored for decreas-
ing flow. The ECM can determine the air
injection flow volume by monitoring the change
in short term fuel trim. The test of the AIR sys- AIR FILTER
T851 / 4.68
tem is performed once each ignition cycle
during the first long hot idle period. If the AIR
related values do not respond as expected, a AIR VACUUM SOLENOID VALVE LOCATION
DTC is flagged. The fault must occur on two
consecutive trips to activate the CHECK
ENGINE MIL. Refer to DTC Summary: Group
16, page 61.

NOTES

T851 / 4.67

47
6.0 Litre V12 / ND Engine Management System

Catalytic Converters
Catalyst monitoring for OBD II
Deterioration of catalytic conversion efficiency will create higher than legally acceptable HC, CO and
NOx exhaust emission.

HEATED OXYGEN SENSORS LOCATION

The efficiency of the catalytic converter system is
monitored and a deterioration in efficiency is
flagged as a fault by the ECM. Monitoring for
catalyst efficiency is achieved by sampling both
the incoming and outgoing exhaust gas at the
primary catalysts. Two oxygen sensors are posi-
tioned in each exhaust downpipe assembly —
one upstream of the primary catalyst and one
downstream of the primary catalyst. By compar-
ing the voltage swings of each set of sensors,
the ECM can detect when catalyst efficiency
drops off.

The catalyst operation is monitored two ways

during steady speed driving:
1 The average downstream HO2S voltage
swings are monitored. If the swing amplitude
is less than the maximum limit, the catalyst is
considered to be operating normally.
2 If the average test is not passed, the upstream
and downstream HO2S values are then
compared. A DTC is flagged if the values do
not correspond to the expected efficient cata-
lyst values. The fault must be flagged three
successive times to activate the CHECK
ENGINE MIL.
T851 / 4.69
Refer to DTC Summary: Group 17, page 61.

NOTE: The CHECK ENGINE MIL will not be

activated for catalyst monitoring faults on 1995
model year vehicles; however, a DTC will
be flagged by the ECM that can be retrieved
using PDU.

NOTES

48
 6.0 Litre V12 / ND Engine Management System

Engine Misfire
Misfire monitoring for OBD II
Engine misfire may cause catalytic converter damage and/or cause a vehicle to fail an emission inspection.

The ECM monitors the engine for individual cylinder misfire by monitoring the engine speed sensor
(RPM Sensor). At each cylinder firing, the crankshaft momentarily accelerates. The ECM records
and compares the time intervals between cylinder firings and the engine sensor pulses.

If a misfire is detected, the ECM flags a DTC that identifies the misfiring cylinder and activates the
CHECK ENGINE MIL. During certain types of misfire, the CHECK ENGINE MIL will flash once per
second, then remain lit if misfiring stops.

There are two levels of misfire that can be detected:

Level 1 If the misfire is not severe but will increase emission levels, the fault must occur on two
consecutive trips before a DTC is flagged.
Level 2 If the misfire is severe enough so that catalyst damage can occur, the DTC is flagged
immediately.
Refer to DTC Summary: Group 13, page 59.

NOTE: The CHECK ENGINE MIL will not be activated (flash or steady ON) for misfire monitoring faults
on 1995 model year vehicles; however, a DTC will be flagged by the ECM.

NOTES

49
6.0 Litre V12 / ND Engine Management System

Vehicle Systems Interfaces

The engine management system interfaces with the instrument pack, the climate control system,
and the transmission control module to provide data and sensor input, and operational control.

Instrument Pack
Low fuel level
The fuel level sensor outputs a fuel level voltage signal to the ECM. When the voltage drops below
a specified value, fuel metering DTCs are disabled. Canceling the fuel metering diagnostics prevents
the ECM from flagging DTCs caused by the vehicle running out of fuel.

Fuel level signal monitoring for OBD II

The fuel level signal is monitored for out of range high or low voltage. If there is a fault, a DTC is flagged
and the CHECK ENGINE MIL is activated immediately. Refer to DTC Summary: Group 9, page 57.

Engine speed
The ECM outputs a shared engine speed signal to the instrument pack, the air conditioning control
module (A/CCM) and the transmission control module (TCM). The engine speed output is generated
by the ECM to give three rectangular wave pulses per engine revolution. The signal duration is 50˚
active per 120˚ of crankshaft rotation.

The instrument pack uses the engine speed signal for tachometer operation.

CHECK ENGINE MIL

If the OBD system detects a fault, the ECM outputs a warning signal (ground) to the instrument pack
for operation of the CHECK ENGINE MIL. Refer to On-Board Diagnostic Facility on pages 2 – 4.

Climate Control
Air conditioning compressor
The ECM controls air conditioning compressor clutch operation from a request made by the climate
control module. When an air conditioning compressor ON request (12 volt signal) is received from the
climate control module, the ECM switches ON the compressor (via the air conditioning compressor
relay). The ECM cancels (or does not switch ON) air conditioning during the following engine condi-
tions: starting, acceleration, high coolant temperature, excessively low idle speed, or the loss of the
request signal.

Engine speed
The ECM-supplied engine speed signal (refer to Instrument Pack: Engine Speed above) is used by the
A/CCM to enable or cancel coolant pump operation and window and mirror heater operation. The signal
is also used for A/CCM diagnostic functions.

NOTES

50
 6.0 Litre V12 / ND Engine Management System

Automatic Transmission
Throttle position
The ECM processes the throttle position input signal from the single track throttle position sensor (TPS)
and supplies the TCM with a pulse width modulated signal to indicate throttle position.

Vehicle road speed

The transmission TCM outputs a road speed signal (pulsed signal) to the ECM. The ECM uses the
signal to determine idle speed control and OBD functions. The TCM receives the signal input from the
transmission output speed sensor.

Vehicle speed input monitoring for OBD II

If a vehicle speed signal is not sensed by the ECM, but other signals indicate vehicle speed ( rpm,
neutral switch, MAP), a DTC is flagged. The fault must occur on two consecutive trips to activate the
CHECK ENGINE MIL. Refer to DTC Summary: Group 19, page 61.

Gear selector position

Gear selector position signals are output to the ECM by the linear gear position switches. When the
gear selector is in R, D, 2 or 3, the signal is 5 volts; when the gear selector is in P or N, the signal is
ground or 0 volts. The ECM uses the gear position inputs to help control idle speed. Refer to Ignition
Control, pages 36 – 40, and Idle Control, pages 41 – 43, for a detailed explanation.

Gear selector position monitoring for OBD II

Gear selector position faults are detected by using two tests. One test monitors for high engine load
or gear change request signals while the gear position is P or N. The other test monitors for engine
starting when the gear position is not P or N. A fault must occur on two consecutive trips before the
CHECK ENGINE MIL is activated. Refer to Systems Readiness Test, page 4, and DTC Summary:
Group 22, page 62.

Engine speed and torque

In addition to the engine speed signal, the ECM supplies the TCM with an engine torque signal.
Refer to Instrument Pack: Engine Speed, page 50. The engine torque signal (derived from injector pulse
duration) is supplied as a pulse width modulated (PWM) signal. The TCM uses the engine speed signal
for diagnostic function. Refer to Torque-Based Transmission Shifting, page 40, for torque signal uses.

Serial Communication
Serial communication between the engine management system and PDU takes place via the serial
communication data link. Only one bidirectional serial line connects to the ECM. Serial communica-
tion is used for engine setup, accessing stored DTCs, fault diagnosis and erasing DTCs.

NOTES

51
6.0 Litre V12 / ND Engine Management System

Crankcase Emission Control

The crankcase ventilation system ports crankcase gases to the air intakes. The oil separator consists
of five cylinders of breather gauze held in place by a sliding-fit retainer. The oil separator is located in
the rear half of the breather chest (engine vee). Hoses run from the breather chest cover to the A and
B bank air intakes. Each hose Y’s at the intake manifold with one connection made downstream of
the throttle valve and one connection made to the air cleaner housing. Both hoses between the Y’s
and the air intakes incorporate restrictors.

CRANKCASE VENTILATION / IDLE AIR CONTROL / EVAPORATIVE PURGE RESTRICTORS

BREATHER HOSES

OIL
SEPARATOR

IDLE AIR CONTROL EVAPORATIVE

MANIFOLD AND VALVE CONTROL VALVE

EVAPORATIVE
CANISTER
ECM

T851 / 4.71

When the engine is running at part load, intake

OIL SEPARATOR BREATHER CHEST manifold vacuum draws the crankcase gases into
COVER
the intake manifold. When the engine is running
at full load (throttle valves fully open), the vacuum
in the air cleaners draws the crankcase gases.
The restrictors ensure that correct gas flow
occurs during all engine operating conditions. As
the crankcase gases pass through the gauze
assembly, oil vapor condenses and drains back to
the sump.

NOTES
BREATHER
BREATHER GAUZE
GAUZE RETAINER

T851 / 4.72A & B

52
 The following DTC section is extracted from the
DTC Summaries manual and is included here as an
aid to understanding the system.
Do not use this information to diagnose vehicle faults.

Always refer to the Model Year specific section contained in

the DTC Summaries manual for accurate information.
 DTC Summary
6.0 Litre V12 / ND Engine Management System

OBD II MONITORING CONDITIONS:

When testing for DTC reoccurrence, it can be determined if the Service Drive Cycle
was of sufficient length by performing a PDU “Systems Readiness Test”.
The Systems Readiness Test occurs automatically when the PDU reads the DTCs from
the ECM memory and reports if a full OBD check has or has not been completed
since the memory was last cleared.

If DTC P1000 is stored in memory, the on-board diagnostic tests have not been completed;
if DTC P1111 is stored in memory, all on-board diagnostic tests have been completed.

53
54
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
P1000 System Readiness Check OBD tests not complete since last memory clear 1 System Readiness Check report only
P1111 System Readiness Check OBD tests completed since last memory clear 1 System Readiness Check report only
7 P0105 HACS circuit malfunction Ignition ON > 5 seconds 1 HACS failure (internal ECM fault)
1 P0106 A Bank MAPS range / performance Engine at normal operating temperature; idle, then accelerate 2 Throttle rod disconnected or incorrectly adjusted
Leaking or blocked hose between MAPS and intake manifold
Blocked gas filter
Failed sensor element
P1106 B Bank MAPS range / performance Engine at normal operating temperature; idle, then accelerate 2 Throttle rod disconnected or incorrectly adjusted
Leaking or blocked hose between MAPS and intake manifold
Blocked gas filter
Failed sensor element
P0107 A Bank MAPS sense circuit low voltage Ignition ON > 5 seconds 1 MAPS disconnected
MAPS to ECM sense wire open circuit or
short circuit to ground
MAPS to ECM power supply wire open circuit or
short circuit to ground
MAPS internal failure
P1107 B Bank MAPS sense circuit low voltage Ignition ON > 5 seconds 1 MAPS disconnected
MAPS to ECM sense wire open circuit or
short circuit to ground
MAPS to ECM power supply wire open circuit or
short circuit to ground
MAPS internal failure
P0108 A Bank MAPS sense circuit high voltage Ignition ON > 5 seconds 1 MAPS to ECM signal ground wire open circuit
MAPS to ECM wiring (supply, sense, signal ground)
short circuit to each other
MAPS sensing circuit short circuit to B+ voltage
MAPS internal failure
P1108 B Bank MAPS sense circuit high voltage Ignition ON > 5 seconds 1 MAPS to ECM signal ground wire open circuit
MAPS to ECM wiring (supply, sense, signal ground)
short circuit to each other
MAPS sensing circuit short circuit to B+ voltage
MAPS internal failure
2 P0111 IATS range / performance Engine idle > 30 seconds 2 IATS power supply failure; short or open circuit
IATS internal failure
P0112 IATS sense circuit high voltage (low air temperature) Ignition ON > 5 seconds 1 IATS disconnected
IATS to ECM wiring open circuit or high resistance
IATS sensing circuit short circuit to B+ voltage
IATS internal failure
P0113 IATS sense circuit low voltage (high air temperature) Ignition ON > 5 seconds 1 IATS to ECM wiring short circuit to ground
IATS internal failure

* Number of consecutive trips required to activate CHECK ENGINE MIL.

 GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
3 P0116 ECTS range / performance Engine at normal operating temperature; idle > 20 minutes 2 Low coolant level
Engine thermostat stuck open
ECTS connector high resistance when hot
ECTS element failure
P0117 ECTS sense circuit high voltage (low coolant temperature) Ignition ON > 5 seconds 1 ECTS disconnected
ECTS to ECM wiring open circuit or high resistance
ECTS sensing circuit short circuit to B+ voltage
ECTS internal failure
P0118 ECTS sense circuit low voltage (high coolant temperature) Ignition ON > 5 minutes 1 ECTS to ECM wiring short circuit to ground
ECTS internal failure
4 P0121 TPS range / performance Engine at normal operating temperature; 2 Blocked air filter
drive steadily at 45 mph Incorrect TPS setting or loose mounting screws
(engine between 1500 – 2000 rpm) > 5 seconds Incorrect throttle linkage setting
TPS power supply failure
MAPS signal incorrect or not sensed
IATS signal incorrect or not sensed
TPS internal failure
P0122 TPS sense circuit low voltage Ignition ON > 5 seconds 1 TPS disconnected
TPS to ECM position sense wire open circuit or
short circuit to ground
TPS to ECM power supply wire open circuit or
short circuit to ground
TPS internal failure
P0123 TPS sense circuit high voltage Ignition ON > 5 seconds 1 TPS to ECM signal ground wire open circuit
TPS to ECM wiring (supply, sense, signal ground)
short circuit to each other
TPS sensing circuit short circuit to B+ voltage
TPS internal failure
3 P0125 Insufficient coolant temperature for closed loop fuel control Engine at normal operating temperature; idle > 20 minutes 2 Low coolant level
Engine thermostat stuck open
ECTS connector high resistance when hot
ECTS internal failure

* Number of consecutive trips required to activate CHECK ENGINE MIL.

55
56
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
5 P0131 HO2S sense circuit low voltage – A bank, upstream (1) Engine at normal operating temperature; 2 HO2S disconnected
drive steadily at 56 mph > 1 minute HO2S to ECM wiring open circuit
(DTC P0131 may flag with warm engine HO2S short circuit to ground
@ 2000 rpm for 3 minutes) HO2S internal failure
P0132 HO2S sense circuit high voltage – A bank, upstream (1) Engine at normal operating temperature; 2 HO2S sensing circuit short circuit to B+ voltage
drive at 56 mph > 1 minute HO2S ground (BRD – braided shield) open circuit
HO2S internal failure
P0133 HO2S sense circuit slow response – A bank, upstream (1) Engine at normal operating temperature; 2 Engine misfire
drive at 56 mph > 1 minute HO2S disconnected
HO2S mechanical damage
HO2S to ECM wiring open circuit
HO2S sensing circuit short circuit to B+ voltage
HO2S short circuit to ground
HO2S ground (BRD – braided shield) open circuit
Exhaust leak
Low exhaust gas temperature
Injector flow partially blocked
Catalyst efficiency decrease
HO2S internal failure
HO2S heater circuit failure
P0134 HO2S sense circuit no activity – A bank, upstream (1) Engine at normal operating temperature; 2 Engine misfire
drive at 56 mph > 1 minute HO2S disconnected
HO2S mechanical damage
HO2S to ECM wiring open circuit
HO2S sensing circuit short circuit to B+ voltage
HO2S short circuit to ground
HO2S ground (BRD – braided shield) open circuit
Exhaust leak
Low exhaust gas temperature
Injector flow partially blocked
Catalyst efficiency decrease
HO2S internal failure
P0135 HO2S heater circuit malfunction – A bank, upstream (1) Engine run > 45 seconds, idle 2 HO2S disconnected
No HO2S heater power supply
HO2S heater to power supply wiring open circuit
HO2S heater to ECM wiring short circuit
HO2S heater to ECM wiring open circuit
HO2S internal failure
P0137 HO2S sense circuit low voltage – A bank, downstream (2) Engine at normal operating temperature; 2 Refer to P0131 possible causes
drive at 56 mph > 1 minute
P0138 HO2S sense circuit high voltage – A bank, downstream (2) Engine at normal operating temperature; 2 Refer to P0132 possible causes
drive at 56 mph > 1 minute
P0139 HO2S sense circuit slow response – A bank, downstream (2) Engine at normal operating temperature; 2 Refer to P0133 possible causes
drive at 56 mph > 1 minute
P0140 HO2S sense circuit no activity – A bank, downstream (2) Engine at normal operating temperature; 2 Refer to P0134 possible causes
drive at 56 mph > 1 minute
P0141 HO2S heater circuit malfunction – A bank, downstream (2) Engine run > 45 seconds, idle 2 Refer to P0135 possible causes
P0151 HO2S sense circuit low voltage – B bank, upstream (1) Engine at normal operating temperature; 2 Refer to P0131 possible causes
drive at 56 mph > 1 minute
(DTC P0131 may flag with warm engine
@ 2000 rpm for 3 minutes)

* Number of consecutive trips required to activate CHECK ENGINE MIL.

 GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
5 P0152 HO2S sense circuit high voltage – B bank, upstream (1) Engine at normal operating temperature; 2 Refer to P0132 possible causes
drive at 56 mph > 1 minute
P0153 HO2S sense circuit slow response – B bank), upstream (1) Engine at normal operating temperature; 2 Refer to P0133 possible causes
drive at 56 mph > 1 minute
P0154 HO2S sense circuit no activity – B bank, upstream (1) Engine at normal operating temperature; 2 Refer to P0134 possible causes
drive at 56 mph > 1 minute
P0155 HO2S heater circuit malfunction – B bank, upstream (1) Engine run > 45 seconds, idle 2 Refer to P0135 possible causes
P0157 HO2S sense circuit low voltage – B bank, downstream (2) Engine at normal operating temperature; 2 Refer to P0131 possible causes
drive at 56 mph > 1 minute
P0158 HO2S sense circuit high voltage – B bank, downstream (2) Engine at normal operating temperature; 2 Refer to P0132 possible causes
drive at 56 mph > 1 minute
P0159 HO2S sense circuit slow response – B bank, downstream (2) Engine at normal operating temperature; 2 Refer to P0133 possible causes
drive at 56 mph > 1 minute
P0160 HO2S sense circuit no activity – B bank, downstream (2) Engine at normal operating temperature; 2 Refer to P0134 possible causes
drive at 56 mph > 1 minute
P0161 HO2S heater circuit malfunction – B bank, downstream (2) Engine run > 45 seconds, idle 2 Refer to P0135 possible causes
6 P0171 A Bank combustion too lean Engine at normal operating temperature; 2 Engine misfire
drive at 56 mph > 1 minute Fuel filter, system blockage
Fuel injector blockage
Fuel injector wiring open circuit
Fuel pressure regulator failure (low fuel pressure)
Low fuel pump output
HO2S harness wiring condition fault
Exhaust leak (before catalyst)
ECM receiving incorrect signal from one or more of the
following components: ECTS, MAPS, TPS, IATS
P0172 A Bank combustion too rich Engine at normal operating temperature; 2 Blocked air filter
drive at 56 mph > 1 minute Fuel system return pipe blockage
Leaking fuel injector
Fuel injector harness short circuit to ground
Fuel pressure regulator failure (high fuel pressure)
ECM receiving incorrect signal from one or more of the
following components: ECTS, MAPS, TPS, IATS
P0174 B Bank combustion too lean Engine at normal operating temperature; 2 Refer to P0171 possible causes
drive at 56 mph > 1 minute
P0175 B Bank combustion too rich Engine at normal operating temperature; 2 Refer to P0172 possible causes
drive at 56 mph > 1 minute
9 P1198 Fuel level sense circuit high voltage Ignition ON > 1 minute 1 Fuel level sense wire short circuit to B+ voltage
Fuel level sense wire open circuit
Fuel level sensor failure
P1199 Fuel level sense circuit low voltage / malfunction Ignition ON > 1 minute 1 Fuel level sense wire short circuit to ground
Fuel level sensor failure

* Number of consecutive trips required to activate CHECK ENGINE MIL.

57
58
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
11 P0201 Fuel injector circuit malfunction – A bank, cylinder 1 Engine at normal operating temperature; 2 Injector disconnected
engine run > 10 seconds Injector harness wiring open or short circuit
(DTC P0201 may flag at fast idle) Injector failure
P0202 Fuel injector circuit malfunction – A bank, cylinder 2 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0202 may flag at fast idle)
P0203 Fuel injector circuit malfunction – A bank, cylinder 3 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0203 may flag at fast idle)
P0204 Fuel injector circuit malfunction – A bank, cylinder 4 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0204 may flag at fast idle)
P0205 Fuel injector circuit malfunction – A bank, cylinder 5 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0205 may flag at fast idle)
P0206 Fuel injector circuit malfunction – A bank, cylinder 6 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0206 may flag at fast idle)
P0207 Fuel injector circuit malfunction – B bank, cylinder 1 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0207 may flag at fast idle)
P0208 Fuel injector circuit malfunction – B bank, cylinder 2 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0208 may flag at fast idle)
P0209 Fuel injector circuit malfunction – B bank, cylinder 3 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0209 may flag at fast idle)
P0210 Fuel injector circuit malfunction – B bank, cylinder 4 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0210 may flag at fast idle)
P0211 Fuel injector circuit malfunction – B bank, cylinder 5 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0211 may flag at fast idle)
P0212 Fuel injector circuit malfunction – B bank, cylinder 6 Engine at normal operating temperature; 2 Refer to P0201 possible causes
engine run > 10 seconds
(DTC P0212 may flag at fast idle)
12 P1240 Sensor power supply malfunction Engine at normal operating temperature; 2 A Bank MAPS, B Bank MAPS and TPS failure DTCs
MAPS and TPS tests complete flagged at once
Refer to P1241 and P1242 possible causes
P1241 Sensor power supply circuit low voltage Ignition ON > 5 seconds 2 MAPS and TPS sensor power supply wire(s)
short circuit to ground
P1242 Sensor power supply circuit high voltage Ignition ON > 5 seconds 2 MAPS and TPS sensor power supply wire(s)
high resistance or short circuit
MAPS and TPS sensor power supply wire(s)
short circuit to B+ voltage
7 P1244 HACS range / performance Ignition ON > 5 seconds; not cranking 2 HACS failure (internal ECM fault)

* Number of consecutive trips required to activate CHECK ENGINE MIL.

 GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
8 P1245 Engine crank signal low voltage Start engine, idle 2 Starter relay coil to ECM wire (parallel circuit to BPM)
open circuit
P1246 Engine crank signal high voltage Engine at normal operating temperature; 2 Starter relay coil to ECM wire (parallel circuit to BPM)
accelerate from stop to 31 mph; short circuit to B+ voltage
decelerate to stop; repeat 5 times Body Processor Module (BPM) fault
13 P0300** Random misfire detected Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Fuel contaminated
Fuel injector(s) blocked or leaking
Ignition secondary circuit breakdown (spark plugs, leads)
Ignition coil pack internal failure
Fuel pressure low
Cylinder compression low
Broken valve spring(s)
P0301** Misfire detected – A bank, cylinder 1 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0302** Misfire detected – A bank, cylinder 2 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0303** Misfire detected – A bank, cylinder 3 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0304** Misfire detected – A bank, cylinder 4 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0305** Misfire detected – A bank, cylinder 5 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0306** Misfire detected – A bank, cylinder 6 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0307** Misfire detected – B bank, cylinder 1 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0308** Misfire detected – B bank, cylinder 2 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0309** Misfire detected – B bank, cylinder 3 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0310** Misfire detected – B bank, cylinder 4 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0311** Misfire detected – B bank, cylinder 5 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P0312** Misfire detected – B bank, cylinder 6 Engine at idle > 2 minutes; drive below 2000 rpm > 2 minutes 1 or 2 Refer to P0300 possible causes
P1313** Catalyst damage misfire detected – A bank Drive with rpm below 2100 at steady speed > 2 minutes 1 Refer to P0300 possible causes
P1314** Catalyst damage misfire detected – B bank Drive with rpm below 2100 at steady speed > 2 minutes 1 Refer to P0300 possible causes
P1316** Misfire excess emission Drive with rpm below 2100 at steady speed > 2 minutes 2 Refer to P0300 possible causes

* Number of consecutive trips required to activate CHECK ENGINE MIL.

** Flagged DTCs P1313, P1314 and P1316 will activate the CHECK ENGINE MIL (1996 model year ON). In addition one or more of the cylinder identification DTCs will be flagged (random misfire P0300 or individual
cylinder P0301 – P0312.

59
60
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
14 P0335 RPM Sensor circuit malfunction Start engine, idle 1 RPM Sensor disconnected
RPM Sensor sensing circuit open circuit
RPM Sensor sensing circuit short circuit to ground
RPM Sensor sensing circuit short circuit to B+ voltage
RPM Sensor internal failure
P1335 CKPS circuit malfunction*** Engine run > 5 seconds, idle 1 CKPS disconnected
CKPS sensing circuit open circuit
CKPS sensing circuit short circuit to ground
CKPS sensing circuit short circuit to B+ voltage
CKPS / crankshaft disc alignment
Damaged or missing pulser ring tooth
CKPS internal failure
P0336 RPM Sensor range / performance*** Start engine, idle 1 Foreign material on RPM Sensor face
RPM Sensor / flywheel disc alignment
Damaged flywheel disc
Excessive crankshaft end float
RPM Sensor internal failure
P1336 CKPS range / performance Engine run > 5 seconds, idle 1 Foreign material on CKPS face
CKPS / crankshaft disc alignment
Damaged or missing pulser ring tooth
CKPS internal failure
P0340 CMPS circuit malfunction*** Engine run > 5 seconds, idle 1 CMPS disconnected
CMPS sensing circuit open circuit
CMPS sensing circuit short circuit to ground
CMPS sensing circuit short circuit to B+ voltage
Damaged or missing CMPS camshaft peg
CMPS internal failure
15 P1367 Ignition monitor – A bank*** Engine run > 10 seconds, idle 1 Ignition module disconnected
Ignition module to ECM harness open circuit
Ignition module to ECM harness short circuit to ground
Ignition module to ECM harness short circuit to B+ voltage
Ignition coil failure
Ignition coil relay failure
Ignition module internal failure
P1368 Ignition monitor – B bank*** Engine run > 10 seconds, idle 1 Refer to P1367 possible causes

* Number of consecutive trips required to activate CHECK ENGINE MIL.

*** Engine must be running to retrieve DTC
 GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
16 P0410 AIR System malfunction Engine at normal operating temperature; 2 AIR pump drive belt failure
start, idle > 30 seconds AIR hose(s) failure
AIR relay power supply failure
AIR relay failure
AIR pump clutch failure
AIR pump internal failure
AIR wiring harness open or short circuit
ASV disconnected (vacuum)
ASV internal failure
AIR VSV wiring harness open or short circuit
AIR check valve internal failure
P0414 AIR system VSV circuit short circuit Fuel system tests complete 2 AIR pump drive belt failure
(Refer to DTCs P0171 and P0172) AIR hose(s) failure
AIR relay power supply failure
AIR relay failure
AIR pump clutch failure
AIR pump internal failure
AIR wiring harness open or short circuit
ASV disconnected (vacuum)
ASV internal failure
AIR VSV wiring harness open or short circuit
AIR check valve internal failure
17 P0420 Catalyst efficiency below threshold – A bank Engine at normal operating temperature; **** Fuel contamination
drive steadily at 35 mph > 3 minutes Exhaust system air leak (before catalyst)
Engine misfire
Catalyst mechanical damage
Downstream HO2S fault present but undetected
Excessive oil consumption
P0430 Catalyst efficiency below threshold – B bank Engine at normal operating temperature; **** Refer to P0420 possible causes
drive steadily at 35 mph > 3 minutes
18 P0441 EVAP system incorrect purge flow – A bank Engine at normal operating temperature; 2 A and B Bank EVAP valve harness connectors reversed
vehicle stopped, idle > 2 minutes; EVAP purge hose blocked or disconnected
fuel tank < 1/2 full; A/C OFF EVAP canister atmosphere vent blocked
EVAP valve failure
P1441 EVAP system incorrect purge flow – B bank Engine at normal operating temperature; 2 Refer to P0441 possible causes
vehicle stopped, idle > 2 minutes;
fuel tank < 1/2 full; A/C OFF
P0433 EVAP valve circuit malfunction – A bank Ignition ON, not cranking > 10 seconds 2 EVAP valve disconnected
ECM to EVAP valve “drive” circuit short circuit to
EVAP valve “supply” circuit
ECM to EVAP valve “drive” circuit short circuit to B+ voltage
EVAP valve internal failure
P1443 EVAP valve circuit malfunction – B bank Ignition ON, not cranking > 10 seconds 2 Refer to P0433 possible causes
19 P0500 Vehicle speed sensor malfunction (signal from TCM) Engine at normal operating temperature; 2 VSS Wiring harness between TCM and ECM
drive at engine speed > 1600 rpm; open or short circuit
release throttle and decelerate 1600 to 1400 rpm in DRIVE, VSS Internal failure
without using brakes

* Number of consecutive trips required to activate CHECK ENGINE MIL.

**** Three successive fail judgments. Diagnostic tests are performed continuously. Use PDU Systems Readiness Test to determine if tests are complete.

61
62
GROUP DTC FAULT DESCRIPTION OBD II MONITORING CONDITIONS (see page 53) TRIPS* POSSIBLE CAUSES
20 P0506 Idle air control system: rpm lower than expected – A bank Engine at normal operating temperature; 2 IACV hoses blocked or leaking
vehicle stopped, idle > 30 seconds IACV disconnected
IACV internal failure
IACV stuck closed (foreign material)
IACV “drive” circuits open or short circuit
Undetected MAPS fault (hose blocked or disconnected)
Incorrect fuel pressure
Misfire
Seized power steering pump
Seized air conditioning compressor
P1506 Idle air control system: rpm lower than expected – B bank Engine at normal operating temperature; 2 Refer to P0506 possible causes
vehicle stopped, idle > 3 minutes
P0507 Idle air control system: rpm higher than expected – A bank Engine at normal operating temperature; 2 IACV disconnected
vehicle stopped, idle > 3 minutes Brake servo diaphragm failure
Intake manifold leak
IACV gasket air leak
IACV stuck open (foreign material)
IACV “drive” circuits open or short circuit
Undetected MAPS fault (hose blocked or disconnected)
Incorrect fuel pressure
TPS setting incorrect
Throttle linkage / valve setting incorrect
P1507 Idle air control system: rpm higher than expected – B bank Engine at normal operating temperature; 2 Refer to P0507 possible causes
vehicle stopped, idle > 3 minutes
21 P1512 TPS Idle switch sense circuit low voltage Accelerate from stop to 35 mph; decelerate to stop; 2 TPS incorrect setting
repeat 5 times TPS harness short circuit to ground
TPS harness short circuit across wires
P1513 TPS Idle switch sense circuit high voltage Accelerate from stop to 35 mph; decelerate to stop; 2 TPS incorrect setting
repeat 5 times TPS disconnected
TPS harness open circuit
22 P1516 Gear change NEUTRAL / DRIVE malfunction Drive steadily at 55 mph > 30 seconds 2 Linear gear position switch setting incorrect
Gear selector cable setting incorrect
Linear gear position switch to ECM wiring harness open circuit
P1517 Engine cranking NEUTRAL / DRIVE malfunction Start engine 2 Linear gear position switch setting incorrect
Gear selector cable setting incorrect
Linear gear position switch wiring harness
short circuit to ground
23 P0603 ECM PECUS programmed data corrupted Ignition ON > 5 seconds 1 ECM failure
25 P0605 ECM ROM data corrupted Ignition ON > 5 seconds 1 ECM failure
10 P1641 Fuel pump relay 1 malfunction Ignition ON > 5 seconds 2 Relay failure
Relay to ECM wiring (coil circuit) open or short circuit
Relay to fuel pump wiring (switched circuit)
open or short circuit
P1646 Fuel pump relay 2 malfunction Ignition ON > 5 seconds 2 Refer to P1641 possible faults
24 P1775 TCM / CHECK ENGINE MIL request Ignition ON > 5 seconds 1 Possible transmission fault – check for flagged TCM DTCs
P1776 Torque reduction request signal duration fault Ignition ON > 5 seconds 1 Torque reduction signal wire open circuit
Torque reduction signal wire short circuit to ground
Torque reduction signal wire short circuit to B+ voltage

* Number of consecutive trips required to activate CHECK ENGINE MIL.

The following Figures and Data pages are extracted from select
Electrical Guides and are included here as an
aid to understanding the Engine Management system.
Do not use this information to diagnose vehicle faults.

Always refer to the Model and Model Year specific

Electrical Guide for accurate information.
6.0 Litre V12 / LM Engine Management System

Contents

6.0 Litre V12 / LM Engine Management System Overview 3–4

Crankcase Breather System 5

Fuel Injection: Overview 6–7

Fuel Delivery 8 – 11

Fuel Injection 12 – 17

Fuel Injection Components 18 – 21

Ignition: Overview 22 – 23

Ignition Timing Control 24 – 25

Ignition Components 26 – 28

1
2
 6.0 Litre V12 / LM Engine Management System

6.0 Litre V12 / LM Engine Management System Overview

The 6.0 litre V12 Lucas / Marelli (V12 / LM) Engine Management System is the same for both
the XJS and the XJ12 Sedan. This system employs a combination Lucas / Marelli fuel injec-
tion / ignition system that incorporates revisions to include new and expanded functions over
the previous 1992 model year 5.3 litre V12 system. In addition to revised ECM functions, sub-
systems that are not ECM controlled have been revised.

6.0 LITRE V12 ENGINE INSTALLATION: XJ12 SEDAN

POWER
IGNITION RESISTORS
POWER MODULE IGNITION IGNITION
A BANK POWER MODULE IDLE SWITCH
B BANK

IGNITION
FUEL INJECTION AIR TEMPERATURE
AIR TEMPERATURE SWITCH
SENSOR

T850/1.01

3
6.0 Litre V12 / LM Engine Management System

6.0 Litre V12 / LM Engine Management System Overview (continued)

6.0 LITRE V12 ENGINE INSTALLATION: XJS

FUEL INJECTION IGNITION
INTAKE AIR TEMPERATURE SENSOR INTAKE AIR
TEMPERATURE
SUPPLEMENTARY SENSOR
AIR VALVE

POWER
RESISTORS

POWER MODULES

T850/1.02

4
 6.0 Litre V12 / LM Engine Management System

Crankcase Breather System

Part-load engine breather system

OIL SEPARATOR
The part-load engine breather system consists
of an air / oil separator chamber, integral with BREATHER
CONNECTIONS JACKSHAFT
the jack shaft cover plate. The system con- COVER PLATE
nects to the intake manifolds down stream of
the throttle housings.

OIL SEPARATOR WITH HOSES CONNECTED

AIR / OIL
SEPARATOR T850/1.03

A BANK UNDERSIDE

AIR / OIL
SEPARATOR

(VIEWED FROM REAR OF ENGINE) T850/1.04

Full-load engine breather

SUPPLEMENTARY
The full load breather is connected from the B AIR VALVE
bank timing cover to the B bank air cleaner
housing.

FULL LOAD BREATHER

T850/1.05

T850/1.06

5
6.0 Litre V12 / LM Engine Management System

Fuel Injection: Overview

The fuel injection system maintains optimum fuel flow control over the entire engine operating
range by precisely metering the fuel into each cylinder. The main parameters for determining fuel
flow requirements are engine load and speed. The ECM senses engine load from intake mani-
fold absolute pressure and engine speed from the ignition pulses.

The ECM incorporates a manifold pressure sensor (transducer) and has a memory with stored
fuel-flow strategy for various combinations of engine load and speed. The ECM receives inputs
from sensors, switches and the ignition system that are applied to its memory to determine the
required fuel flow.

The 36CU ECM incorporates new and expanded function over the previous 26CU ECM. The
complete range of fuel injection ECM functions is as follows:

• ECM self-test
• Fuel delivery (fuel pumps A and B)
• Fuel injection
• Cold start
• Warm-up
• Exhaust oxygen content feedback
• Fuel cutoff during engine overrun
• Evaporative canister purge control
• Adaptive idle fueling trim
• Air injection control
• Hot start system timing
• Fuel level sensing
• Fuel fail output to transmission control module
• Fuel monitoring (trip computer)
• On Board Diagnostics (OBD) with “Limp home” capability
• Serial Communications (ISO)

NOTE: The sensors and switches are unique to the fuel injection system and are not used or
shared by the digital ignition system.

6
 FUEL PUMP RELAY 2 AIR
INJECT. ECM
FUEL PUMP RELAY 1 RELAY

AIR INJECTION
SOLENOID AIR INJECTION
FUEL FUEL PUMP
PUMP B PUMP A VAC. VALVE
PRESSURE
REGULATOR
FUEL TANK
DELAY
HOT START VALVE THROTTLE
FILTER SWITCH ECM
FUEL RAIL POSITION
SENSOR
HOT START SOL. VAC. VALVE FUEL PUMP
INJECTOR CONTROL MODULE
ECM
INTAKE AIR
ECM ENGINE SPEED
AIR
COOLANT INJ.
TEMP.
SENSOR AIR TEMP. SUPP. AIR
SENSOR VALVE
DISTRIBUTOR
ECM
6.0 LITRE ENGINE MANAGEMENT SYSTEM: XJ12 SEDAN

A / C CLUTCH
ECM
O2 SENSORS
IGNITION FUEL
ECM EXTRA PUMP
AIR VALVE RELAY 2 FUEL PUMP B

FUEL
EXHAUST PUMP FUEL PUMP A
RELAY 1

MANIFOLD O2 SENS.
ABSOLUTE OXYGEN SENSOR
HEATER HEATERS
IGNITION PULSES: PRESSURE RELAY
FUEL INJECTION ECM, COOLANT TEMP. SENSOR SENSOR
FUEL PUMP CONTROL MODULE
THROTTLE POSITION SENSOR
INERTIA
EFI SWITCH
AIR TEMP. SENSOR MAIN
RELAY IGNITION
OXYGEN SENSORS
AIR INJECTION RELAY
IGNITION PULSES PURGE VALVES
(ENGINE SPEED)
INJECTORS FUEL INFORMATION (TRIP COMPUTER)
FUEL FAIL (TRANSMISSION)
CHECK ENGINE WARNING
POWER
RESISTORS DIAGNOSTIC TROUBLE CODES
FUEL INJECTION
ECM SERIAL COMMUNICATIONS

T850/1.07

7
6.0 Litre V12 / LM Engine Management System
6.0 Litre V12 / LM Engine Management System

Fuel Delivery

In order to meet the fuel requirements of the 6.0 litre engine, two fuel pump modules are used.
The modules are identical but operate independently with staged control. One pump runs con-
tinuously when the engine is running, the other is activated when the engine speed exceeds
2840 rpm. Each pump is activated by a separate relay.

FUEL PUMP CONTROL MODULE The fuel pump control module, located on the
trunk right side, receives an engine speed
input from the Ignition ECM and switches the
relay 2 coil ground as follows. When the engine
speed reaches 2840 rpm, the ground is com-
pleted; as the engine speed decreases, the
ground is interrupted at 2000 rpm. Switching of
fuel pump B requires just 1/4 of a second, ensur-
ing instant response for additional fuel delivery.

XJ12 Sedan
T850/1.10
The two fuel pump relays are switched by the
Fuel Injection ECM via the oxygen sensor
heaters relay; however, the coil circuit of relay
2 is completed to ground via the fuel pump
control module.

FUEL PUMP CONTROL: XJ12 SEDAN FUEL PUMPS: XJ12 SEDAN

FUEL
INJECTION
ECM
IGNITION ON

OXYGEN
SENSOR
HEATERS
RELAY T850/1.08

OXYGEN SENSOR HEATERS

FUEL
FUEL FUEL PUMP
PUMP PUMP CONTROL ENGINE SPEED
RELAY 1 RELAY 2 MODULE

FUEL FUEL
PUMP PUMP
A B

T850/1.11

8
 6.0 Litre V12 / LM Engine Management System

XJS
Fuel pump relay 1 is switched by the Fuel
Injection ECM. Fuel pump relay 2 is switched
by the fuel pump control module.

FUEL PUMPS: XJS FUEL PUMP CONTROL: XJS

IGNITION ON

EMS: FI
MAIN
RELAY

ENGINE SPEED

FUEL
FUEL FUEL FUEL PUMP
INJECTION PUMP PUMP CONTROL
ECM RELAY 1 RELAY 2 MODULE
T850/1.09

FUEL FUEL
PUMP PUMP
A B

T850/1.12

9
6.0 Litre V12 / LM Engine Management System

Fuel Delivery (continued)

FUEL PRESSURE REGULATOR

Fuel pressure regulator
The fuel pressure regulator maintains the fuel
rail pressure at 44 psi (3 bar).

Evaporative emission control

The evaporative emission control system uses
the same canister and vacuum / pressure relief
valve as the 4.0 liter XJS and the Sedan
Range. Two purge control valves, one for
each cylinder bank, are located at the charcoal
canister. The purge valves are controlled by
the fuel injection ECM. The ECM opens the
valves simultaneously, according to an engine
load and speed strategy, allowing purge flow
to both intake manifolds. Purge flow is en-
T850/1.13 abled at idle after adaptive idle fueling is
completed. The charcoal canister is located at
the front of the left front wheel arch.
CHARCOAL CANISTER: XJS

PURGE VALVES

VACUUM / PRESSURE
RELIEF VALVE
T850/1.14

10
 ROLL-OVER VALVE PRESSURE
EVAPORATIVE RELIEF VALVE
FLANGE FUEL RAIL

FUEL INJ.
INTAKE INTAKE
MANIFOLD MANIFOLD

RETURN
FUEL FILTERS
PUMPS FUEL
PUMP PRES.
INLET FILTERS REG.
FILTERS
VENT
FUEL TANK FUEL PUMP FUEL PUMP
MODULE MODULE

FILTER
FUEL DELIVERY AND EVAPORATIVE EMISSION CONTROL SYSTEM

RESTRICTOR PURGE
VALVES

VACUUM / PRESSURE
RELIEF VALVE
(ROCHESTER VALVE)
FUEL ENGINE LOAD
INJECTION
ECM
ENGINE SPEED

CHARCOAL IGNITION SWITCHED

CANISTER POWER SUPPLY

T850/1.15

11
6.0 Litre V12 / LM Engine Management System
6.0 Litre V12 / LM Engine Management System

Fuel Injection

FUEL INJECTION CONTROL

Fuel metering control
Fuel metering is obtained by controlling the
injector pulse duration (on-time) during each
engine cycle (two crankshaft rotations). The
pulse duration is varied by the engine control
module (ECM) according to several sensor
ENGINE CONTROL MODULE
inputs. The sensed control inputs form two
groups — primary and secondary. Primary
control inputs are intake manifold absolute
MANIFOLD
ABSOLUTE PRESSURE pressure (MAP) and engine speed; secondary
PRESSURE TRANSDUCER
(ENGINE LOAD)
control inputs consist of engine coolant tem-
perature, intake air temperature, throttle
movement and position, exhaust oxygen con-
tent, cranking signal and battery voltage. The
injectors are triggered via the power resistors,
MANIFOLD PRESSURE
ENGINE SPEED V in staggered groups of six. Except during
ENGINE SPEED
starting and sudden throttle opening, injector
pulses occur every third ignition pulse (once
per engine revolution).

Primary control
ENGINE MOVING Fuel metering is controlled primarily as a func-
COOLANT TEMP. THROTTLE
tion of intake manifold absolute pressure
INTAKE AIR CORRECTION TRIMS CLOSED OR
TEMP. FACTORS WIDE-OPEN (MAP) and engine speed. Manifold pressure
THROTTLE is sensed by a pressure transducer located in
CRANKING EXHAUST OXYGEN
CONTENT the engine control module and connected to
FEEDBACK the A bank manifold by a vacuum line. Engine
speed is sensed from an ignition ECM output.

Fueling strategies are held in memory (EPROM)

BATTERY VOLTAGE BATTERY
CORRECTION VOLTAGE in the ECM and form a manifold pressure v
engine speed matrix. Injector pulse duration is
then calculated according to secondary correc-
tion factors and trims. The resulting injector
pulse duration is further modified to account
INJECTOR PULSE for battery voltage.
DURATION

Injection timing depends on the crankshaft

position and the ECM internal state at start-up.
The ECM internal state is determined from the
IGNITION FUEL INJECTION crankshaft position when the engine was last
PULSE TIMING
stopped and the ECM state when the ignition
was turned off.

INJECTOR(S)
(STAGGERED GROUPS OF SIX)

T850/1.16

12
 6.0 Litre V12 / LM Engine Management System

Secondary control
Secondary fueling enrichment is provided for engine starting, warm-up and throttle response at
all temperatures within the engine’s operating range.

Coolant temperature The coolant temperature sensor provides an electrical input to the ECM.
During engine starting and warm-up, enrichment is provided by increasing the injector pulse
duration when coolant temperature is below normal operating temperature. Enrichment is
reduced with increasing engine speed and load.

Engine starting At engine cranking speeds, the ECM increases the number of injector pulses
to three per engine revolution. It also increases the injector pulse duration in relation to coolant
temperature sensor input. As engine speed increases, cranking enrichment is reduced to tran-
sition to the warm-up phase.

After start enrichment After engine start-up, the ECM increases the injector pulse duration
above the normal running requirement and then decreases the pulse duration as a function of
elapsed time after engine start.

Throttle movement and position The throttle position sensor provides electrical signals to the
ECM for opened and closed throttle operation as well as throttle movement during acceleration
and deceleration. In order to ensure good response when rapid throttle opening occurs, the ECM
triggers an extra injector pulse to all injectors simultaneously. The duration of the extra pulse is
dependent on coolant temperature.

Intake air temperature Fuel metering is adjusted to vary approximately with the density of the
engine intake air. Intake air density is sensed by measuring the air temperature at the right air
intakes.

Full load Full load fuel metering varies with throttle position and engine speed. Under full load
conditions, exhaust oxygen sensor closed loop control is disabled.

Air / fuel ratio (closed loop control) In order to achieve optimum performance from the
exhaust three-way catalyst system, the exhaust oxygen content is monitored and controlled by
trimming the fuel metering. Two oxygen sensors are used: one in each exhaust down-pipe, after
the primary catalyst. Closed loop control is disabled under these conditions:

• during engine warm-up when the air injection is operating

• during full load operation
• during deceleration fuel cutoff (engine overrun).

Battery voltage The time necessary for full injector open and close to occur varies with battery
voltage. For example, with low battery voltage, the time necessary for full injector open to
occur is long; therefore, less fuel is delivered for a given pulse duration. The opposite is true for
high battery voltage. The ECM corrects the injector pulse duration to achieve the fuel delivery
that would be obtained at a nominal reference voltage.

13
6.0 Litre V12 / LM Engine Management System

Fuel Injection (continued)

Adaptive idle fueling trim

In order to ensure optimum performance throughout the life of the vehicle, the fuel injection ECM
software contains an adaptive idle fueling function that automatically trims the fuel injector idle
pulse duration strategy, The total available trim to the nominal injector pulse duration is ± 20%.
This function eliminates the manual adjustment of idle trim. Adaptive fueling is performed by the
ECM software only when there are no diagnostic trouble codes (DTCs) present, and the listed
preconditions are met.

Adaptive idle fueling preconditions:

• Throttle closed
• Engine speed below 900 rpm
• Air injection disabled after engine start
• Closed loop fueling control enabled

If there are no DTCs present and the preconditions are met, the ECM cancels purge flow and
adapts the idle fueling. Between fueling adaptations, there is a delay of approximately eight min-
utes during which the preconditions must be met. If the preconditions are interrupted, the delay
will be lengthened.

Air injection
The 6.0 litre air injection system is similar to the AJ6 4.0 litre air injection system. An air injec-
tion pump with an electric clutch, and a vacuum operated air cutoff valve are controlled by the
fuel injection ECM. Air injection is enabled after all engine starts. The ECM uses a strategy com-
prised of a number of injector pulses versus engine coolant temperature for air injection
switch-off. Air injection is enabled following all hot starts and always operates below 115°F (47°C)
engine coolant temperature. The air shut-off valve is operated by vacuum applied by the sole-
noid vacuum valve when signaled from the ECM.

NOTE: The XJS air injection pump is operationally the same as the XJ12 pump, however, it is
manufactured by a different supplier.

AIR INJECTION

FUEL
ENGINE START INJECTION
ECM DELAY VALVE
COOLANT TEMPERATURE RIGHT
INTAKE MANIFOLD
AIR INJECTION
RELAY

SOLENOID
HOT START VACUUM VALVE
SYSTEM

A BANK
AIR INJECTION RAIL

CHECK VALVE

AIR CUT-OFF
VALVE
B BANK
AIR INJECTION RAIL AIR PUMP
CHECK VALVE
T850/1.17

14
 6.0 Litre V12 / LM Engine Management System

Hot start system

The hot start system remains the same as the previous 5.3 liter system with the exception of the
timing control. The function of the previous 45-second timer is replaced by fuel injection ECM
control. When air injection is enabled, current is applied to the hot start switch. If the fuel rail
temperature is 158°F (70°C) or above, the switch closes and activates the solenoid vacuum valve.
The solenoid vacuum valve is mounted on the front of the right throttle body. The activated valve
closes and directs vacuum to the fuel pressure regulator through the delay valve. The momen-
tary vacuum delay increases fuel pressure to purge the fuel rail.

HOT START SYSTEM

FUEL RAIL FUEL PRESSURE

REGULATOR

HOT START
FUEL SWITCH

ENGINE START INJECTION

ECM
COOLANT TEMPERATURE
AIR INJECTION
RELAY AIR INJECTION
SYSTEM

SOLENOID
VACUUM VALVE DELAY VALVE

RIGHT
INTAKE MANIFOLD

T850/1.18

Idle speed control

Base idle speed control is maintained solely by the adjustable idle air bleed at the extra air valve.

Idle speed stabilization Idle speed stabilization is enabled when the air conditioning compressor
is operating. The supplementary air valve is activated with the compressor clutch to allow throttle-
valve-bypass air flow to the right intake manifold. The valve operates in all gear selector positions.

15
6.0 Litre V12 / LM Engine Management System

Fuel Injection (continued)

OVERRUN FUEL CUTOFF

Fuel Cutoff
Overrun fuel cutoff To improve fuel
THROTTLE
FUEL INJECTION ECM economy and aid in controlling exhaust emis-
POSITION:
CLOSED sions, the ECM cuts off fuel injection during
engine overrun conditions. The ECM deter-
ENGINE SPEED mines overrun conditions from throttle position
(VARIABLE)
(throttle position sensor), engine speed (ignition
pulses) and coolant temperature.
COOLANT TEMP.
(VARIABLE)
Coolant Cutoff Reinstatement
Temperature RPM RPM
Up to -5°F 5000 4000
(-15°C)
32°F(0°C) 3000 2000
NO
FUEL INJECTION 50°F(10°C) 2000 1500
T850/1.19
68°F(20°C) 1900 1400
86°F(30°C) 1900 1400
WIDE OPEN THROTTLE AT CRANKING 104°F(40°C) 1800 1300
149°F(65°C) 1500 1100
FUEL INJECTION ECM and above
THROTTLE
POSITION:
WIDE OPEN
Wide Open Throttle during cranking When
the ECM senses that the throttle is wide open
ENGINE SPEED (throttle position sensor) during cranking (<200
< 200 RPM rpm, ignition pulse input), fuel injection is can-
celed to prevent the engine from flooding.

NO
FUEL INJECTION
T850/1.20

On-Board Diagnostics System (OBD)

The ECM includes a fault diagnosis facility that continuously monitors the operation of the engine
management sensors and components. If a fault is detected, the OBD system will activate the
CHECK ENGINE warning in the instrument pack and on the trip computer display. In addition, it
will flag a diagnostic trouble code (DTC) in the ECM memory. The ECM can, at any time, be in-
terrogated through the trip computer display by switching off the ignition then switching on the
ignition. The CHECK ENGINE warning will display and the DTC will appear 5 seconds later. If
two or more DTCs are flagged in memory, only the highest priority code will be displayed. The
remaining codes will be displayed, in turn, as the faults are corrected and erased from memory.

NOTE: In order to prevent the erroneous flagging of codes, a fuel level input (voltage) to the fuel
injection ECM is supplied. The ECM will not flag DTCs 13, 18, 19, 23, 34, 36, 44 and 45 when
the fuel tank level falls below approximately 1 gallon.

16
 6.0 Litre V12 / LM Engine Management System

Serial communications
Serial communications between the engine management system and JDS or PDU are available
via the serial communications data link connector located in the trunk. Serial communication is
used for engine setup, fault diagnosis and erasing diagnostic trouble codes.

Limp home mode

In order to allow vehicle operation if a malfunction occurs, “limp home” default strategies are
incorporated as an ECM facility. The ECM will substitute a nominal value for missing inputs from
various sensors and components.

Diagnostic trouble code summary

The available DTCs are listed in order of priority on the following table. Limp home mode is avail-
able as indicated. When multiple faults occur, only the highest priority code will be displayed.

DTC Limp Home Mode Input or Component checked

29 ECM Self-test
44 X Oxygen sensor circuit — A bank
45 X Oxygen sensor circuit — B bank
13 X Manifold pressure transducer and sensing hose
34 Injector electrical circuits — A bank
36 Injector electrical circuits — B bank
14 X Coolant temperature sensor circuit
17 X Throttle position sensor circuit
18 X Manifold pressure transducer / throttle position sensor circuit
(high throttle voltage / low MAP)
19 X Manifold pressure transducer / throttle position sensor circuit
(low throttle voltage / high MAP)
23 Fuel metering at idle — banks A and B combined
49 X Power resistors electrical circuits
11 X Pressure transducer / throttle position sensor circuit
16 X Intake air temperature sensor circuit
67 Air injection operation (oxygen sensor response)
77 Engine speed (loss of input from ignition ECM)

Clearing diagnostic trouble codes

All DTCs are held in the ECM memory until cleared using serial communication. If the vehicle
battery is disconnected, the DTC(s) will be cleared.

17
6.0 Litre V12 / LM Engine Management System

Fuel Injection Components

36CU ENGINE CONTROL MODULE: FUEL INJECTION

Engine control module (ECM): Fuel Injection
Location Trunk, right front.
Description The 36CU ECM contains an inte-
grated circuit for a dedicated fuel injection
control chip and an analog / digital converter
for the manifold pressure input. A manifold
absolute pressure sensor (transducer) is built
into the ECM. Fuel injection information is
stored in ROM (read only memory), so that for
a given combination of manifold pressure and
engine speed, the memory assigns a number
proportional to the required injector pulse du-
ration. The ECM also contains facilities for
OBD and serial communications.
T850/1.21

Fuel injectors
Location Intake manifolds.
FUEL INJECTOR
Description Each fuel injector contains a
solenoid-operated needle valve, which is held
against a seat by spring pressure. When ener-
gized, the coil moves the needle away from
the seat, allowing pressurized fuel to flow
through the tip.

Power resistors
Location Engine compartment: right bulk-
T850/1.22 head (XJ12); right front (XJS).
Description The power resistor pack contains
four 6-ohm resistors. Each resistor is con-
POWER RESISTOR
nected to a group of 3 injectors to limit the
current during the “hold” portion of the injec-
tor pulse duration. Limiting the current
protects the ECM.

Throttle position sensor

Location Under the throttle turntable.
Description The twin track throttle position
sensor is mechanically connected to the
T850/1.23
throttle valve shaft and provides a reference
voltage input to the ECM dependent on
throttle position and rate of acceleration. The
THROTTLE POSITION SENSOR
second track is used by the transmission con-
trol system.

T850/1.24

18
 6.0 Litre V12 / LM Engine Management System

Coolant temperature sensor

COOLANT TEMPERATURE SENSOR
Location Left thermostat housing.
Description The coolant temperature sensor
is a temperature-sensitive resistor. As the cool-
ant temperature rises, the electrical resistance
decreases providing a coolant temperature
input to the ECM.

Coolant Temp. Resistance Voltage

(°F) (°C) (kilohms) (±)
14 -10 9.2 3.27
T850/1.25
32 0 5.9 3.11
50 10 3.7 2.91
78 20 2.5 2.66
86 30 1.7 2.38 AIR TEMPERATURE SENSOR
104 40 1.18 2.07
122 50 0.84 1.76
140 60 0.60 1.48
158 70 0.435 1.22
176 80 0.325 0.99
193 90 0.250 0.80
212 100 0.190 0.65

Intake air temperature sensor

Location Right air cleaner intake (XJ12); right
air cleaner (XJS). T850/1.26

Description The air temperature sensor is a

temperature-sensitive resistor. As the ambi-
OXYGEN SENSOR
ent (intake) air temperature rises, the electrical
resistance decreases providing an input to the
ECM. The ECM uses this input as a measure
of intake air density (as air temperature rises,
its density decreases).

Air Temp. Resistance Voltage

(°F) (°C) (kilohms) (±)
14 -10 9.2 3.27
32 0 5.9 3.11
50 10 3.7 2.91
78 20 2.5 2.66
86 30 1.7 2.38
104 40 1.18 2.07
122 50 0.84 1.76
140 60 0.60 1.48 T850/1.27

Oxygen sensor
Location Exhaust down-pipes.
Description The oxygen sensors (2) measure
the oxygen concentration in the exhaust gases
and provide an input to the ECM.

19
6.0 Litre V12 / LM Engine Management System

Fuel Injection Components (continued)

EXTRA AIR VALVE

Extra air valve
Location Left cylinder head, rear.
Description The extra air valve has two func-
tions: it provides the engine base idle speed
through the adjustable idle air bleed, and it pro-
vides warm-up idle speed stabilization through
the variable air duct. The duct area is varied by
a temperature sensitive expansion element, in
contact with engine coolant, that moves a con-
trol piston. As the coolant temperature
increases, the area of the duct is gradually
reduced until, at a coolant temperature of 140
to 158°F, it closes completely.

Supplementary air valve

Location Right air cleaner back plate.
INTAKE MANIFOLDS Description The supplementary air valve
allows additional throttle bypass air into the
intake manifolds to stabilize the idle speed dur-
PRESSURE SPRING ing air conditioning compressor operation. The
valve operates in all gear selector positions.
CONTROL
FROM PISTON
AIR CLEANER

PERMANENT
AIR BLEED

IDLE AIR
ADJUSTMENT
EXPANSION
ELEMENT

T850/1.28, 1.29

SUPPLEMENTARY AIR VALVE

T850/1.30

20
 6.0 Litre V12 / LM Engine Management System

Hot start switch HOT START SWITCH

Location Fuel rail, right.
Description The hot start switch switches
current between the air injection relay
(switched by the ECM) and the hot start sole-
noid vacuum valve. The switch contacts close
at 158°F and above.

Hot start solenoid vacuum valve

Location Above right thermostat housing.
Description The normally open solenoid T850/1.31

vacuum valve closes when current is applied.

Air injection solenoid vacuum valve HOT START SOLENOID VACUUM VALVE
Location Right cylinder head, rear.
Description The normally closed solenoid
vacuum valve opens when current is applied.

Purge valves
Location Right front inner fender (XJ12); char-
coal canister (XJS).
Description The purge valve is a solenoid
operated valve that is normally open. The valve
closing and subsequent rate of vapor flow T850/1.32

(opening) is varied by the “length” of the

pulsed electrical signal provided from the ECM.
AIR INJECTION SOLENOID VACUUM VALVE

T850/1.33

PURGE VALVE

PURGE FLOW

T850/1.34

21
6.0 Litre V12 / LM Engine Management System

Ignition: Overview

The ignition system is a digital microprocessor controlled system that eliminates vacuum and
mechanical advance controls. The microprocessor memory contains ignition timing strategy with
precise timing for engine speeds, loads, and modes of operation. The microprocessor, in the
ignition ECM, receives inputs from engine sensors to program the necessary ignition timing. The
double-deck two-rotor distributor distributes the high tension voltage to A bank (right) via the
lower deck and to B bank (left) via the upper deck. The low-voltage circuit is switched by the
ignition ECM via the two power modules to the two ignition coils. High voltage is generated by
the ignition coils and supplied to the distributor.

The inputs supplied to the ECM from the engine sensors form two groups of control parameters:
primary inputs and secondary inputs. The crankshaft position and engine-speed inputs are nec-
essary for the engine to start. The remaining inputs effect engine operation but are not necessary
for engine start.

Primary Inputs
• Crankshaft position — TDC sensor
• Engine speed — engine speed (flywheel) sensor
• Engine load — manifold absolute pressure sensor

Secondary Inputs
• Throttle position — idle switch
• Intake air temperature — air temperature switch

Other Functions
• Engine speed output
• Ignition retard (torque reduction) during transmission shift

NOTE: The sensors and switches are unique to the digital ignition system and are not used or
shared by the fuel injection system.

Engine speed outputs

The ignition ECM provides engine speed outputs for the following:
• Tachometer
• Fuel injection control
• Fuel pump B control
• Transmission control

22
 AIR
TEMP. IGNITION COILS
SENSOR
6.0 LITRE V12 IGNITION CONTROL

IDLE
SWITCH POWER
MODULES

ENGINE TDC
SPEED SENSOR
SENSOR
MAN. ABSOLUTE
PRESSURE SENS.

BATTERY
POWER

IGNITION
SWITCH

IGNITION RETARD REQUEST (TRANSMISSION)

IGNITION RETARD ACKNOWLEDGE

ENGINE SPEED –
TACHOMETER; FUEL INJECTION ECM;
TRANSMISSION CONTROL MODULE;
FUEL PUMP CONTROL MODULE
IGNITION ECM

T850/1.35

23
6.0 Litre V12 / LM Engine Management System
6.0 Litre V12 / LM Engine Management System

Ignition Timing Control

IGNITION TIMING SYNCHRONIZATION

Ignition timing synchronization
During all engine operating modes, the crank-
ECM: IGNITION shaft position sensor (TDC sensor) input is
used by the ECM to time spark delivery.
Crankshaft position is referenced from A bank.
The ECM times spark delivery for both banks
PRESSURE
TRANSDUCER from the A bank reference.

Engine starting
Ignition timing during cranking and start-up is
determined from engine speed, intake air tem-
perature and throttle position. Ignition timing
IGNITION STRATEGIES
moves from engine starting to normal running
at 350 rpm.

Engine speed is obtained from the engine

speed (flywheel) sensor; intake air temperature
CRANKSHAFT IGNITION is obtained from the intake air temperature sen-
TIMING
POSTIION sor; throttle position is obtained from the
throttle switch.

POWER MODULES
T850/1.36

ENGINE STARTING

ECM: IGNITION

PRESSURE
TRANSDUCER

FIXED
ENGINE SPEED STARTING IGNITION
(LESS THAN TIMING
350 RPM)

CRANKSHAFT IGNITION
POSTITION TIMING

POWER MODULES
T850/1.37

24
 6.0 Litre V12 / LM Engine Management System

Closed throttle running CLOSED THROTTLE RUNNING

Ignition timing during closed throttle operation
ECM: IGNITION
is programmed separately for idle and decel-
eration. Closed throttle running is enabled by
the ECM from the idle switch input.
PRESSURE
TRANSDUCER
When the idle switch is closed, the ECM does
not recognize the engine load (manifold abso-
lute pressure sensor) input and uses the idle
portion of the ignition strategy for ignition tim-
ENGINE
ing. The idle strategy uses engine speed and SPEED IGNITION IDLE
STRATEGY
intake air temperature. INTAKE AIR
TEMPERATURE
Engine speed is obtained from the engine
speed (flywheel) sensor; engine intake air tem-
perature is obtained from the intake air
IGNITION
temperature sensor. CRANKSHAFT
TIMING
POSITION

Open throttle running

Ignition timing during open throttle running is
determined by primary inputs from engine
speed and engine load and from secondary
inputs from intake air temperature. Engine POWER MODULES T850/1.38

speed is obtained from the engine speed (fly-

wheel) sensor; engine load is obtained from
the manifold absolute pressure sensor; intake OPEN THROTTLE RUNNING
air temperature is obtained from the intake air ECM: IGNITION
temperature sensor.

The ECM memory incorporates an ignition tim- MANIFOLD

ABSOLUTE PRESSURE
ing strategy with ignition timing information PRESSURE TRANSDUCER
stored for 16 engine load and 16 engine speed (ENGINE LOAD)

sites. A value number relating to the required

ignition timing is generated from the strategy
based on the engine load and speed inputs. If
the engine load and speed is between sites, a ENGINE SPEED
IGNITION TIMING
STRATEGY
value number is calculated from the surrounding
sites. The ignition timing requirement is then
modified depending on intake air temperature.

Ignition retard / transmission control INTAKE AIR

INTAKE AIR TEMPERATURE
The ignition ECM receives an ignition retard TEMPERATURE CORRECTION
request from the transmission control module
during certain transmission apply and release
functions. Before the transmission completes
the function, an acknowledgment of the request CRANKSHAFT IGNITION
is made by the ignition ECM. The momentary POSITION TIMING

ignition retard reduces engine torque to ensure

a “quality” shift. Ignition timing is retarded up to
20° with a limit of 8° ATDC. The retard is applied
for a maximum of 1.2 seconds after which the
ECM gradually returns to the engine speed / load
POWER MODULES
strategy over a 0.5 second period. T850/1.39

25
6.0 Litre V12 / LM Engine Management System

Ignition Components

ENGINE CONTROL MODULE: IGNITION

Engine control module (ECM): Ignition
Location Front passenger footwell, A post
trim panel.
Description The ECM contains the micropro-
cessor for receiving analog inputs from the
engine sensors and producing the ignition tim-
ing, which is accessed and delivered from the
ignition strategy stored in the memory. Inte-
gral in the ECM is the manifold absolute
pressure sensor.

Top dead-center sensor

Location Front crankshaft pulley.
Description The sensor is triggered by a
three toothed reluctor to produce a TDC refer-
T850/1.40
ence for A bank.

TOP DEAD-CENTER SENSOR

Engine speed sensor
Location Flywheel ring gear.
Description The sensor is triggered by the
flywheel ring gear teeth, which act as a
reluctor to produce an engine speed input to
the ECM.

RESISTANCE: 700 – 800 OHMS

T850/1.41

ENGINE SPEED SENSOR

RESISTANCE: 700 – 800 OHMS

T850/1.42

26
 6.0 Litre V12 / LM Engine Management System

Idle switch IDLE SWITCH

Location Throttle turntable.
Description The micro switch closes when
the throttle is closed, signaling the ECM that
the engine is at idle or decelerating.

Intake air temperature sensor

Location Right air cleaner back plate.
Description The intake air temperature sen-
sor is a temperature-sensitive resistor. As the
air temperature rises, the electrical resistance
decreases providing an air temperature input
to the ECM.

T850/1.43

INTAKE AIR TEMPERATURE SENSOR

T850/1.44

27
6.0 Litre V12 / LM Engine Management System

Ignition Components (continued)

POWER MODULE
Power modules
Location Front bulkhead component panel
(XJ12); upper radiator support (XJS).
Description The power modules switch the
low voltage circuit to ground when signaled by
the ECM.

Ignition coils
Location Engine vee: A bank – red ident on
harness plug; B bank – yellow ident on har-
ness plug.
Description The ignition coils generate high
voltage current for distribution to the spark
plugs.
T850/1.45
Distributor
Location Engine vee.
IGNITION COIL Description The distributor is a double-deck
design with the upper rotor distributing high
voltage current to B bank spark plugs and the
lower rotor distributing high voltage current to
A bank spark plugs.

T850/1.46

DISTRIBUTOR

T850/1.47

28
The following Figures and Data pages are extracted from select
Electrical Guides and are included here as an
aid to understanding the Engine Management system.
Do not use this information to diagnose vehicle faults.

Always refer to the Model and Model Year specific

Electrical Guide for accurate information.
 5.3 Litre Engine Management

Contents

System Introduction 2

1992 Model Year

Crankcase Emission Control 3

Engine Management System:

Fuel Injection — Overview 4–5

Fuel Delivery 6 – 10

Fuel Distribution 11

Engine Management System: Fuel Injection 12 – 16

Additional Fuel Injection ECM Functions 17

Fuel Injection Components 18 – 23

1989 – 90 Model Years

System Variations 24 – 25

Fuel Delivery 26 – 28

Engine Management System 29 – 30

Fuel Injection Components 31

1989 – 92 Model Years

Engine Management System:

Ignition — Overview 33 – 34

Ignition: Engine Operating Modes 34 – 35

Ignition Components 37 – 39

1
5.3 Litre Engine Management

System Introduction

The 5.3 litre V12 engine uses electronic systems, vacuum systems and air injection to govern
engine and engine-related functions. These are independent systems; however, they are depen-
dent on each other to achieve an overall efficiency of operation, while providing precise control
over each individual function. The independent systems should be thought of as one engine man-
agement system when evaluating engine performance.

1992 Model Year Although the engine management system remained fundamentally similar to
previous 5.3 litre V12 systems, many of the components were new and the operation was re-
vised. In the interest of clarity, a complete 1992 model year system description is detailed first
followed by the differences for the earlier 1989 / 90 model year system.

5.3 Litre V12 tuning specifications:

Firing order 1A 6B 5A 2B 3A 4B 6A 1B 2A 5B 4A 3B
(A bank – right; B bank – left)
Idle speed 800 rpm (+50 - 0 rpm)
Fuel pressure 28.5 – 30 psi in fuel rail (vacuum connected at idle)
Spark plug gap 0.024 – 0.028 in.
(1992 MY)
Engine speed sensor gap 0.018 – 0.042 in.
TDC sensor gap 0.018 – 0.042 in.

2
1992 Model Year 5.3 Litre Engine Management

Crankcase Emission Control

Crankcase ventilation
Piston blowby gases are scavenged from the crankcase and the camshaft housings via the left
timing housing and the camshaft covers. The gases are collected and fed into the engine through
the left air cleaner.

5.3 LITRE V12 CRANKCASE EMISSION CONTROL

PCV VALVE

T850/2.01

3
5.3 Litre Engine Management 1992 Model Year

Engine Management System: Fuel Injection — Overview

Starting in model year 1992, the fuel injection system employed a new fuel injection engine con-
trol module (26 CU) and revised components and subsystems.

The fuel injection system maintains optimum fuel flow control over the entire engine operating
range by precisely metering the fuel into each cylinder. The main parameters for determining fuel
flow requirements are engine load and speed. The ECM senses engine load from intake mani-
fold absolute pressure and engine speed from the ignition pulses.

The ECM incorporates a manifold pressure sensor (transducer) and has a memory with stored
fuel-flow strategy for various combinations of engine load and speed. The ECM receives inputs
from sensors, switches and the ignition system that are applied to its memory to determine the
required fuel flow.

The 26CU ECM incorporates an expanded strategy that provided more precise control over the
full range of fuel injection control. In particular, starting and warm-up control were expanded and
refined. A facility for On Board Diagnostics (OBD) that stores fault data during engine operation
was added. Diagnostic trouble codes (DTCs) are displayed on the center console message dis-
play. Additionally, a serial communications serial link is used to access the stored fault data and
test the system.

The complete range of fuel injection ECM functions is as follows:

• ECM self-test
• Fuel delivery (fuel pump)
• Fuel injection
• Cold start
• Warm-up
• Exhaust Oxygen Content feedback
• Fuel cutoff during engine overrun
• “Limp home” capability
• Collision safety
• Fuel monitoring (trip computer)
• On Board Diagnostics (OBD)
• Serial Communications (ISO)

NOTE: The sensors and switches are unique to the fuel injection system and are not used or
shared by the digital ignition system.

4
 FUEL PUMP RELAY 45-SECOND TIMER

AIR INJECTION AIR

SOLENOID SWITCHING
VAC. VALVE VALVE
DELAY
PRESSURE VALVE
REGULATOR
FUEL TANK
DELAY
1992 Model Year

VALVE THERMAL
FILTER HOT START VACUUM
FUEL RAIL SWITCH VALVE ECM
THROTTLE INTAKE AIR TEMP.
POSITION SENS. SENSOR
HOT START SOL. VAC. VALVE ECM
INJECTOR
ECU
INTAKE AIR
ECM
AIR
COOLANT INJ.
TEMP.
SENSOR SUPP. AIR A / C CLUTCH
VALVE
DISTRIBUTOR
IDLE
RELAY
ECM GEAR SELECTOR
(NEUTRAL, PARK)
OXYGEN
SENSORS
IGNITION
ECU EXTRA
AIR VALVE HOT START
SOLENOID
VAC. VALVE
5.3 LITRE V12 ENGINE MANAGEMENT SYSTEM: FUEL INJECTION (1992 MY)

AIR INJECTION
EXHAUST SOLENOID
VAC. VALVE
MANIFOLD
ABSOLUTE 45 SEC.
ECM PRESSURE TIMER
(IGNITION PULSES) COOLANT TEMP. SENSOR SENSOR

THROTTLE POSITION SENSOR INERTIA

ECM
EFI SWITCH
INTAKE AIR TEMP. SENSOR MAIN
RELAY IGNITION
OXYGEN SENSORS

DIAGNOSTICS
IGNITION PULSES
(ENGINE SPEED)
INJECTORS FUEL
PUMP FUEL
RELAY PUMP

POWER
RESISTORS

T850/2.02

5
5.3 Litre Engine Management
5.3 Litre Engine Management 1992 Model Year

Fuel Delivery

The fuel delivery system follows the same principals and layout as the system in Sedan Range
vehicles from 1991 model year on. The fuel pump is part of an in-tank fuel pump module that
gives superior fuel handling qualities under varying conditions and reduces operating noise. An
external filter is located under the vehicle. Approximate fuel tank capacity: 23.5 gallons (Coupe),
21.6 gallons (Convertible).

FUEL DELIVERY SYSTEM (1992 MY)

FUEL FILTER

VACUUM / PRESSURE PURGE VALVES

RELIEF VALVE
(ROCHESTER VALVE) T850/2.03

Fuel lines and connectors

Steel braided PTFE hoses run between the fuel tank flange and the steel underbody lines. Flex-
ible plastic hoses that can be clamped during service operations are used in the engine
compartment. Quick fit connectors are used throughout the system (except for internal fuel tank,
fuel filter, and fuel rail connections). Feed lines have 3/8 in. connectors; return lines have 8 mm
connectors.

6
 INTAKE
FUEL RAIL MANIFOLD
PRESSURE
ROLL-OVER VALVE EVAPORATIVE RELIEF VALVE INTAKE
FLANGE MANIFOLD FUEL INJ.
1992 Model Year

THROTTLE
HOUSING

FUEL PUMP RETURN

MODULE FILTER FUEL
PRES.
FUEL REG.
PUMP PUMP
INLET FILTER
FILTER
VENT PURGE
CONTROL
FUEL TANK

FILTER
HOT START
FUEL DELIVERY AND EVAPORATIVE EMISSION CONTROL SYSTEM : XJS (1992 MY)

PURGE
VALVES

VACUUM / PRESSURE
RELIEF VALVE
(ROCHESTER VALVE)

CHARCOAL
CANISTER

T850/2.04

7
5.3 Litre Engine Management
5.3 Litre Engine Management 1992 Model Year

Fuel Delivery (continued)

Fuel tank
The fuel tank assemblies are similar for Coupe and Convertible models with the exception of the
filler necks. The previous sump tank was eliminated.

Fuel pump module

The fuel pump is contained in a module that mounts in a rubber holder attached to the bottom
of the fuel tank on brackets. The fuel pump module and the rubber holder are indexed to ensure
correct alignment in the tank. The design diverts some of the fuel flow from the pump through
a venturi to maintain full fuel in the module at all times. Fuel enters the module through a
70-micron filter then into the pump inlet through a 400 micron filter. Returning fuel from the
engine fuel rail enters the module through a 70-micron filter. Both the outlet and return feed ports
into the pump module have check valves. The outlet check valve reduces backflow from the fuel
rail when the pump is off. The return check valve prevents siphoning of the fuel tank when the
fuel line is disconnected. Two rubber hoses connect the assembly to the tank inlet and outlet
bosses. The hoses are retained by clamps that are installed and removed with special tool
JD 175. Electrical connection to the pump is made through the evaporative loss flange.

Fuel pump specifications:

Speed 7000 rpm
Flow rate 170 litres per hour
Current 8 – 9 amps @ 13.2 volts

Tool JD 175 is a nonferrous wrench for use when loosening / tightening in-tank fuel hose clamps.
Using JD 175 will eliminate the possibility of a spark being created.

Evaporative loss flange

The removable evaporative loss flange allows installation and removal of the fuel pump assem-
bly, provides three outlet ports for evaporative loss and provides electrical connection to the fuel
pump. Additionally, the flange incorporates a pressure relief valve in the vent port and a roll-over
valve in the evaporative emissions port. The flange is retained by a locking ring that requires
special tool JD 174 for installation and removal.

Fuel level sensing

The instrument pack low fuel warning illuminates with approximately 3.2 gallons of fuel remaining
in the tank. An anti-slosh module in the circuit dampens the low level warning by delaying the
signal 20 seconds.

8
1992 Model Year 5.3 Litre Engine Management

FUEL TANK ASSEMBLY

CONVERTIBLE FILLER NECK

EVAPORATIVE FLANGE

FUEL PUMP
MODULE

INDEX

FUEL LEVEL TRANSMITTER

RUBBER HOLDER

T850/2.05

9
5.3 Litre Engine Management 1992 Model Year

Fuel Delivery (continued)

Evaporative emission control

The fuel tank design includes a lengthened fill tube that limits the fill level and allows for 10% fuel
expansion. Tank venting is via the fuel tank evaporative flange. From there, a tube leads to the
charcoal canister located in the left front wheel well. Vapor flow to the canister is controlled by
a pressure / vacuum relief (Rochester) valve that holds 1 – 1.25 psi when the engine is not run-
ning. Fuel tank pressure is released to the canister upon engine start-up.

The system incorporates two safety pressure relief valves that vent to the atmosphere: a 2-psi
relief valve in the evaporative flange and a 4 psi relief valve in the fill cap.

Canister purging is accomplished by a two-stage system. Two purge control valves are vacuum-
controlled from two left throttle body ports via a thermal vacuum valve. The vacuum ports are
situated so that there is no purge when the throttle plate is in the idle position. Progressive purge
is obtained as the throttle is opened. The thermal vacuum valve controls both vacuum circuits.
The vapor flows to the intake manifolds via the crankcase breather pipe.

At engine coolant temperatures of 95°F and above, the thermal vacuum valve opens allowing
canister purge. As the throttle plate moves off idle, the first vacuum port is exposed applying
vacuum to the first stage purge valve. Further throttle plate movement exposes the second
vacuum port and vacuum is applied to the second stage purge valve. A delay valve in the sec-
ond stage further delays full canister purge as the engine speed increases preventing an over-rich
fuel mixture.

PURGE CONTROL
LEFT
THROTTLE HOUSING

THERMAL
VACUUM VALVE

DELAY VALVE

(2 ND STAGE)

ENGINE COOLANT
PURGE
VALVES

(1 ST STAGE)

FUEL TANK
VAPOR

CHARCOAL
CANISTER
T850/2.06

10
1992 Model Year 5.3 Litre Engine Management

Fuel Distribution

The fuel rail assembly, fuel injectors, and fuel pressure regulator were all new in the 1992 model
year system.

FUEL RAIL ASSEMBLY

B BANK FUEL INJECTORS

(LEFT)

A BANK FUEL INJECTORS

(RIGHT
FUEL PRESSURE
REGULATOR

HOT START SWITCH

T850/2.07

Injectors The injectors are smaller and lighter and allow a lower mounted fuel rail. The injectors
are refined to give improved control of fuel flow at small pulse widths. Connection to the fuel rail
is by ‘O’ rings and clips.

Fuel rail The fuel rail has improved flow characteristics to allow equal injector fuel flow. The rail
assembly is comprised of two separate rails joined by two hoses. The assembly is secured to
the manifolds by integral lugs. The need for a fuel cooler is eliminated by the improved hot fuel
handling capacity of the revised system.

Fuel pressure regulator A single 36-psi regulator mounts in a cast housing connected to the
fuel rail. The vacuum signal from the right intake manifold to the regulator passes through a
solenoid vacuum valve that is a component of the hot start system.

11
5.3 Litre Engine Management 1992 Model Year

Engine Management System: Fuel Injection

Primary inputs
The fuel injectors are triggered and held open by electrical pulses that operate the injector sole-
noid valves. Injector pulse duration determines the quantity of fuel injected and is primarily
determined by engine load and speed. The fuel injection ECM uses the input from the manifold
absolute pressure sensor and ignition pulses to output the required injector pulse duration from
its memory. The injectors are triggered via the power resistors, in staggered groups of six.
Except during starting and sudden throttle opening, injector pulses occur every third ignition pulse
(once per engine revolution).

FUEL INJECTION INPUTS

PRIMARY INPUTS CORRECTION INPUTS

ENGINE LOAD CRANKING

FUEL INJECTION ECM
ENGINE TEMPERATURE

AIR DENSITY (TEMP.)

ENGINE SPEED DEMAND

VOLTAGE

EMISSIONS
INJECTOR PULSE DURATION

T850/2.08

Correction inputs
Additional correction inputs are used by the ECM to vary injector pulse duration as necessary.

Cranking enrichment At engine cranking speeds, the ECM increases the number of injector
pulses to three per engine revolution. It also increases the injector pulse duration in relation to
coolant temperature sensor input. As engine speed increases, cranking enrichment is reduced
to transition to the warm-up phase.

Engine warm-up correction During warm-up, the ECM lengthens the injector pulse duration
in response to the input received from the coolant temperature sensor. Enrichment is reduced
as engine speed increases.

Air density correction Intake air density is sensed by temperature measurement and supplied
to the ECM as an input. The ECM alters the injector pulse duration to lean or enrich the fuel flow
as necessary.

12
1992 Model Year 5.3 Litre Engine Management

Demand corrections During acceleration and full power demands, the injector pulse duration
is lengthened by the ECM in response to input received from the throttle position sensor.

Voltage correction The system uses stabilized voltage for sensing and injector operation.

Emission corrections “Closed loop” exhaust emission control is provided by inputs from the
two heated oxygen sensors. At coolant temperatures below 95°F and for 45 seconds after start-
up, air injection is applied to the exhaust manifolds. During this period, inputs form the oxygen
sensors are not used by the ECM.

IDLE SPEED CONTROL

INTAKE AIR

A / C CLUTCH
SUPP. AIR
VALVE

IDLE
RELAY
GEAR SELECTOR
(NEUTRAL, PARK)

EXTRA
AIR VALVE

T850/2.09

Idle speed
Base idle The base idle speed is set with the adjustment screw on the extra air valve. The
adjustment regulates the throttle valve bypass idle air flow.

Warm-up Dependent on engine coolant temperature, the extra air valve allows additional air to
bypass the throttle valve to maintain idle speed during warm-up.

Idle stabilization During air conditioning compressor operation, the supplementary air valve is
opened via the de-energized idle relay, allowing additional throttle-valve bypass and stabilizing the
idle speed. To prevent excessive idle speed with no engine load (neutral, park), the idle relay is
energized to switch off the supplementary air valve.

13
5.3 Litre Engine Management 1992 Model Year

Engine Management System: Fuel Injection (continued)

OVERRUN FUEL CUTOFF

Overrun fuel cutoff
To improve fuel economy and aid in controlling
exhaust emissions, the ECM cuts off fuel in-
jection during engine overrun conditions. The
THROTTLE
ECM determines overrun conditions from
POSITION:
FUEL INJECTION ECM throttle position (throttle position sensor), en-
CLOSED
gine speed (ignition pulses) and coolant
temperature.
ENGINE SPEED
(VARIABLE)
Coolant Cutoff Reinstatement
COOLANT TEMP. Temperature RPM RPM
(VARIABLE)
Up to -5°F 5000 4000
(-15°C)
32°F(0°C) 3000 2000
50°F(10°C) 2000 1500
68°F(20°C) 1900 1400
NO
FUEL INJECTION 86°F(30°C) 1900 1400
104°F(40°C) 1800 1300
T850/2.10 149°F(65°C) 1500 1100
and above

WIDE OPEN THROTTLE AT CRANKING Wide Open Throttle during cranking

When the ECM senses that the throttle is
wide open (throttle position sensor) during
cranking (<200 rpm, ignition pulse input), fuel
FUEL INJECTION ECM
injection is canceled to prevent the engine
THROTTLE from flooding.
POSITION:
WIDE OPEN

ENGINE SPEED
< 200 RPM

NO
FUEL INJECTION

T850/2.11

14
1992 Model Year 5.3 Litre Engine Management

Hot start HOT START COMPONENTS

During conditions of high underhood tempera-
tures, a hot start system aids in engine starting
by increasing fuel pressure and purging the FUEL RAIL
fuel rail. The system consists of: a fuel rail
temperature sensitive switch, a 45-second
timer and a normally open solenoid vacuum
valve located in the fuel pressure regulator
vacuum line. During normal operation, FUEL PRESSURE
HOT START REGULATOR
vacuum is applied to the regulator through the SWITCH
solenoid vacuum valve.

Each time the ignition is switched ON, the RIGHT INTAKE

45-second timer is activated and applies cur- MANIFOLD
rent to the hot start switch. If the fuel rail SOLENOID VACUUM
VALVE
temperature is 158°F or above, the switch
closes and allows current flow to close the
solenoid vacuum valve. Vacuum to the regu-
lator is delayed causing the regulator to
momentarily increase fuel pressure to purge
the fuel rail.

T850/2.12

HOT START SYSTEM

FUEL RAIL

FUEL PRESSURE
REGULATOR
HOT START
SWITCH

IGNITION

45-SECOND
TIMER

SOLENOID
VACUUM VALVE
DELAY
VALVE

RIGHT
INTAKE MANIFOLD

T850/2.13

15
5.3 Litre Engine Management 1992 Model Year

Engine Management System: Fuel Injection (continued)

Air injection
Secondary air is delivered to the exhaust manifolds during the initial engine warm-up period to
aid oxidation. The rotary vane air pump is belt driven from the crankshaft pulley. Air is delivered
to the exhaust manifolds via the air switching valve, which is controlled by either a thermal
vacuum valve or the 45-second timer via a solenoid vacuum valve. The vacuum circuit also con-
tains a delay valve.

Each time the ignition is switched ON, the 45-second timer is activated and the normally closed
solenoid vacuum valve is opened. If the coolant temperature is below 95° F, the thermal vacuum
valve opens. Manifold vacuum is applied to the air switching valve for 45 seconds after start-up
or until the coolant temperature reaches 95°F, which ever is longer. The delay valve prevents
vacuum loss to the air switching valve when the throttle is suddenly opened.

AIR INJECTION SYSTEM

RIGHT
INTAKE MANIFOLD

45-SECOND
TIMER DELAY VALVE

AIR
IGNITION PUMP
AIR
THERMAL
CLEANER
VACUUM
VALVE AIR
SWITCHING
EXHAUST VALVE
PORTS

IGNITION ENGINE COOLANT

SOLENOID
VACUUM VALVE
T850/2.14

AIR INJECTION CHECK VALVES

Air injection rails
The air injection rails are designed to clear the
revised fuel rail. This arrangement uses two
check valves located at the rear of the engine.

T850/2.15

16
1992 Model Year 5.3 Litre Engine Management

Additional Fuel Injection ECM functions

Collision Safety
In the event of a vehicle impact, the inertia switch will switch off all power supply to the system.
The fuel pump will cease to operate, preventing fuel flow to the engine compartment.

Serial Communications (ISO)

A serial communications serial link is used to access stored fault data in the OBD facility. In ad-
dition, the serial link allows ECM input and output values to be transmitted to check the current
status of the system. The serial link connector is the brown PM 4 located under the passenger’s
center console kick panel.

On-Board Diagnostics
A facility for on-board diagnostics (OBD) that stores fault data during engine operation is contained
in the ECM.

Limp home A “limp home” facility is provided in the memory of the ECM. This facility will al-
low engine operation in the event of system failure(s). The ECM will substitute a nominal value
for missing inputs from the coolant temperature sensor, air temperature sensor, throttle position
sensor, oxygen sensor(s), and the manifold pressure sensor.

Check Engine; Diagnostic Trouble Codes If a fault occurs in the system, a diagnostic trouble
code (DTC) is generated. The CHECK ENGINE warning is immediately displayed on the center
console message display. If the ignition is switched off, and then on, the CHECK ENGINE warn-
ing is displayed with the DTC appearing five seconds later. When the engine is cranked, the
message is cleared and the clock displays. The CHECK ENGINE warning and DTCs will be dis-
played at every ignition cycle.

Diagnostic trouble codes (listed in order of priority):

Code Fault area Limp home Failure
29 ECM self-test NO Checks microprocessor function
44 Oxygen sensor — A bank (right) YES No oxygen sensor response to fueling change (A bank)
45 Oxygen sensor — B bank (left) YES No oxygen sensor response to fueling change (B bank)
13 Manifold absolute pressure sensor YES Manifold pressure does not change on engine starts or
manifold pressure is out of range
34 Fuel injectors or air leak — A bank (right) NO Poor feedback control — rich or lean (A bank)
36 Fuel injectors or air leak — B bank (left) NO Poor feedback control — rich or lean (B bank)
14 Coolant temperature sensor YES Sensor voltage does not change after engine start or
sensor voltage is out of normal range
17 Throttle position sensor YES Throttle position sensor voltage is out of normal range
18 Calibration 1 (engine speed, YES High throttle position sensor voltage / low load pressure,
manifold throttle position) (manifold pressure)
19 Calibration 2 (engine speed, YES Low throttle position sensor voltage / high load pressure,
manifold throttle position) (manifold pressure)
23 Fuel supply NO Poor feedback control — both banks rich or lean
49 Power resistors YES No current through power resistors
11 ECM idle potentiometer YES Idle trim potentiometer is out of normal range
16 Air temperature sensor YES Sensor voltage is out of normal range

NOTE: When multiple faults occur, only the highest priority code will be displayed.

17
18
APPROXIMATE LOCATIONS

AIR INJECTION
SOLENOID VACUUM VALVE THROTTLE POSITION SENSOR

AIR INJECTION
THERMAL VACUUM EXTRA AIR
VALVE VALVE

HOT START
SWITCH

OXYGEN
FUEL INJECTION COMPONENT LOCATIONS (1992 MY)

OXYGEN
5.3 Litre Engine Management

SENSOR
SENSOR

SUPPLEMENTARY CANISTER PURGE

AIR VALVE THERMAL VACUUM
VALVE
HOT START
SOLENOID COOLANT
VACUUM VALVE TEMPERATURE
SENSOR
AIR SWITCHING
VALVE INTAKE AIR
TEMPERATURE
SENSOR

POWER RESISTORS

FUEL PRESSURE
AIR INJECTION PUMP REGULATOR

NOTE: ECM IS LOCATED IN TRUNK, RIGHT FRONT;

45-SECOND TIMER IS LOCATED ON RIGHT COMPONENT PANEL

T850/2.16
1992 Model Year
1992 Model Year 5.3 Litre Engine Management

Fuel Injection Components

Engine control module (ECM): Fuel injection 26CU ENGINE CONTROL MODULE: FUEL INJECTION
Location Trunk, right front.
Description The 26CU ECM contains an inte-
grated circuit for a dedicated fuel injection
control chip and an analog / digital converter
for the manifold pressure input. A manifold
absolute pressure sensor (transducer) is built
into the ECM. Fuel injection information is
stored in ROM (read only memory), so that for
a given combination of manifold pressure and
engine speed, the memory assigns a number
proportional to the required injector pulse du-
ration. The ECM also contains facilities for
OBD and serial communications.

Fuel injectors T850/2.17

Location Intake manifolds.

Description Each fuel injector contains a FUEL INJECTOR
solenoid-operated needle valve, which is held
against a seat by spring pressure. When ener-
gized, the coil moves the needle away from
the seat, allowing pressurized fuel to flow
through the tip.

Power resistors
Location Engine compartment, right front.
Description The power resistor pack contains
four 6-ohm resistors. Each resistor is con-
nected to a group of 3 injectors to limit the
current during the “hold” portion of the injec-
tor pulse duration. Limiting the current
protects the ECM.
T850/2.18

POWER RESISTOR

T850/2.19

19
5.3 Litre Engine Management 1992 Model Year

Fuel Injection Components (continued)

THROTTLE POSITION SENSOR Throttle position sensor

Location Under the throttle turntable.
Description The throttle position sensor is
mechanically connected to the throttle valve
shaft and provides a reference voltage input to
the ECM dependent on throttle position.

Coolant temperature sensor

Location Left thermostat housing.
Description The coolant temperature sensor
T850/2.20 is a temperature-sensitive resistor. As the
coolant temperature rises, the electrical resis-
tance decreases providing a coolant
COOLANT TEMPERATURE SENSOR temperature input to the ECM.

Intake air temperature sensor

Location Left air cleaner intake.
Description The air temperature sensor is a
temperature-sensitive resistor. As the ambi-
ent (intake) air temperature rises, the electrical
resistance decreases providing an input to the
ECM. The ECM uses this input as a measure
of intake air density (as air temperature rises,
T850/2.21 its density decreases).

Oxygen sensor
AIR TEMPERATURE SENSOR
Location Exhaust down pipes.
Description The oxygen sensors (2) measure
the oxygen concentration in the exhaust gases
and provide an input to the ECM.

T850/2.22

OXYGEN SENSOR

T850/2.23

20
1992 Model Year 5.3 Litre Engine Management

Extra air valve EXTRA AIR VALVE

Location Left cylinder head, rear.
Description The extra air valve has two func-
tions: it provides the engine base idle speed
through the adjustable idle air bleed, and it pro-
vides warm-up idle speed stabilization through
the variable air duct. The duct area is varied by
a temperature sensitive expansion element, in
contact with engine coolant, that moves a con-
trol piston. As the coolant temperature
increases, the area of the duct is gradually
reduced until, at a coolant temperature of 140
to 158°F, it closes completely.

Supplementary air valve

Location Right air cleaner back plate.
Description The supplementary air valve INTAKE MANIFOLDS
allows additional throttle bypass air into the
intake manifolds to stabilize the idle speed dur-
ing air conditioning compressor operation PRESSURE SPRING

(except when in neutral or park).

CONTROL
FROM PISTON
AIR CLEANER

PERMANENT
AIR BLEED

IDLE AIR
ADJUSTMENT
EXPANSION
ELEMENT

T850/2.24, 2.25

SUPPLEMENTARY AIR VALVE

T850/2.26

21
5.3 Litre Engine Management 1992 Model Year

Fuel Injection Components (continued)

INERTIA SWITCH
Inertia switch
Location Passenger’s side ‘A’ post.
Description In the event of a vehicle impact,
the inertia switch switches off all power sup-
ply the engine management system.

Hot start switch

Location Fuel rail, right.
Description The hot start switch switches
current between the 45-second timer and the
hot start solenoid vacuum valve. The switch
contacts close at 158°F and above.

Hot start solenoid vacuum valve

T850/2.27
Location Above right thermostat housing.
Description The normally open solenoid
vacuum valve closes when the circuit is com-
HOT START SWITCH pleted via the 45-second timer and the hot
start switch.

T850/2.28

HOT START SOLENOID VACUUM VALVE

T850/2.29

22
1992 Model Year 5.3 Litre Engine Management

Air injection solenoid vacuum valve AIR INJECTION SOLENOID VACUUM VALVE
Location Right cylinder head, rear.
Description The normally closed solenoid
vacuum valve opens when the circuit is com-
pleted via the 45-second timer.

Air switching valve

Location Engine, right front.
Description The air switching valve directs air
injection to the exhaust manifolds or the air
cleaner dependent on vacuum signal.

45-second timer
Location Right component panel.
Description The 45-second timer provides a T850/2.30

timed ground for 45 seconds each time the

ignition is switched on.
AIR SWITCHING VALVE

T850/2.31

45-SECOND TIMER

T850/2.32

23
5.3 Litre Engine Management 1989 – 90 Model Years

System Variations

The 5.3 litre engine management system used in 1989 and 1990 model year vehicles is similar
in construction and operation to the 1992 system. The following variations in the fuel injection
system should be noted:

• Fuel delivery system with external sump tank, fuel pump and fuel cooler
• Evaporative emission system with vapor separator
• Fuel rail with hose connection to injectors and two pressure regulators
• Fuel injection ECM without self-test; specification differences (cranking enrichment, etc.)
• Full throttle enrichment via mechanical and vacuum switches
• Hot start system without timer control
• Air injection system without timer control
• No On-Board Diagnostics (OBD)
• No “limp home” facility
• No serial communications (ISO)

The complete range of fuel injection 16CU ECM functions is as follows:

• Fuel delivery (fuel pump)
• Fuel injection
• Cold start
• Warm-up
• Exhaust emissions feedback
• Fuel cutoff during engine overrun
• Collision safety

NOTE: The sensors and switches are unique to the fuel system and are not used or shared by
the digital ignition system.

24
 FULL THROTTLE
MICRO SWITCH
THROTTLE ECU
FUEL TANK TURNTABLE
OUTLET ECU
PRESSURE
REGULATORS THROTTLE
PUMP ECM POSITION SENSOR
FILTER INLET
FUEL RAIL FULL
THROTTLE
1989 – 90 Model Years

VAC. SWITCH ECM

RIGHT THERM. VAC. AIR TEMP.
FUEL PUMP MAN. INJECTOR VALVE SENSOR
RELAY
ECM
INTAKE AIR
ECM
AIR
COOLANT TEMP. SENSOR INJ.
SUPP. AIR A/C CLUTCH
VALVE
DISTRIBUTOR
IDLE
RELAY
ECM
02
SENSOR (2)
IGNITION
ECM EXTRA GEAR SELECTOR
AIR VALVE (NEUTRAL, PARK)
PULSE START
DAMPER
5.3 LITRE V12 ENGINE MANAGEMENT SYSTEM: FUEL INJECTION (1989 – 90 MY)

RELAY
EXHAUST
START

MANIFOLD
ABSOLUTE FUEL
ECM PRESSURE PUMP
(IGNITION PULSES) SENSORS SENSOR
PUMP
THROTTLE SWITCHES RELAY
ECM

IGNITION PULSES INERTIA

SWITCH
MAIN
INJECTORS RELAY
IGNITION

POWER
RESISTORS

T850/2.33

25
5.3 Litre Engine Management
5.3 Litre Engine Management 1989 – 90 Model Years

Fuel Delivery

A recirculating fuel delivery system is used to provide a continuous supply of pressurized fuel to
the fuel rail.

Fuel is drawn from the small sump through a pre-filter by an external electric pump and delivered
to the fuel rail through a renewable filter. The pump incorporates a check valve.

Two pressure regulators are used on the fuel rail. The inlet regulator maintains fuel pressure in
the delivery line; the outlet regulator controls fuel pressure in the fuel rail. Both regulators sense
intake manifold absolute pressure. The outlet regulator sensing line passes through a thermal
vacuum valve controlled by fuel rail temperature. Fuel pressure in the rail is controlled so that the
pressure drop across the injector nozzles is maintained at approximately 36 psi. The inlet regu-
lator is set at 45± psi; the outlet regulator is set at 36± psi.

If the temperature of the fuel rail exceeds a specified temperature, the thermal vacuum valve
closes the intake manifold sensing port and vents the regulator sensing line to the atmosphere.
When this occurs, the regulator interprets the atmospheric pressure as full throttle (maximum
manifold pressure) and increases fuel pressure in the rail to maximum. The increased fuel pres-
sure prevents vapor formation in the fuel rail at high underhood temperatures and purges the fuel
rail for hot starts.

The fuel pump is activated by the ECM when the ignition is switched on. If no immediate cranking
occurs, the ECM activates the pump for two seconds only to raise the pressure in the fuel rail and
then switches it off to prevent flooding. After cranking has started, the ECM switches on the pump.

Returning fuel is cooled by the fuel cooler when the air conditioning compressor is operating.
Convertible models have a fuel temperature sensing circuit that independently operates the air
conditioning compressor.

26
 RIGHT INTAKE FUEL RAIL LEFT INTAKE
VAPOR MANIFOLD MANIFOLD
SEPARATOR
FUEL INJ.
THROTTLE
HOUSING

SUMP THERM.
TANK VAC.
1989 – 90 Model Years

VENT VALVE

OUTLET
INLET FUEL PRESS.
FUEL PRESS. REG.
FUEL TANK REG.

SUMP
TANK
DELAY
FUEL PUMP FILTER VALVE

PRE FILTER
THERMAL
VACUUM
VALVE
FUEL DELIVERY AND EVAPORATIVE EMISSION CONTROL: XJS (1990 MY)

FUEL COOLER

PURGE
PURGE
VALVES
VALVE

VACUUM / PRESSURE
RELIEF VALVE
(ROCHESTER VALVE)

NOTE: VIN 177468 ON VEHICLES ARE EQUIPPED

CHARCOAL WITH 1992 MY EVAPORATIVE EMISSION SYSTEM
CANISTER

T850/2.34

27
5.3 Litre Engine Management
5.3 Litre Engine Management 1989 – 90 Model Years

Fuel Delivery (continued)

Evaporative emission control

The fuel tank design includes a lengthened fill tube that limits the fill level and allows for 10% fuel
expansion. Tank venting is via the fuel tank vapor separator. From there, a tube leads to the
charcoal canister located in the left front wheel well. Vapor flow to the canister is controlled by
a pressure / vacuum relief (Rochester) valve that holds 1 – 1.25 psi when the engine is not run-
ning. Fuel tank pressure is released to the canister upon engine start-up.

Canister purging is accomplished by a two stage system. Two purge control valves are vacuum
controlled from two left throttle body ports, one via a delay valve. The vacuum ports are situated
so that there is no purge when the throttle plate is in the idle position. Progressive purge is
obtained as the throttle is opened. Purge flow to the intake manifolds flows through a third purge
valve controlled by a thermal vacuum valve. The vapor flows to the intake manifolds via the crank-
case breather pipe.

At engine coolant temperatures of 95°F and above, the thermal vacuum valve opens allowing can-
ister purge. As the throttle plate moves off idle, the first vacuum port is exposed applying vacuum
to the first stage purge valve. Further throttle plate movement exposes the second vacuum port
and vacuum is applied to the second stage purge valve. A delay valve in the second stage fur-
ther delays full canister purge as the engine speed increases preventing an over-rich fuel mixture.

CANISTER PURGE (1990 MY)

LEFT
THROTTLE HOUSING

DELAY VALVE

(2 ND STAGE)

THERMAL
VACUUM VALVE
PURGE
VALVES
ENGINE COOLANT

(1 ST STAGE)

FUEL TANK
VAPOR
NOTE: VIN 177468 ON VEHICLES ARE EQUIPPED
WITH 1992 MY CANISTER PURGE SYSTEM
CHARCOAL
CANISTER

T850/2.35

28
1989 – 90 Model Years 5.3 Litre Engine Management

Engine Management System: Fuel Injection

Primary inputs
The fuel injectors are triggered and held open by electrical pulses that operate the injector solenoid
valves. Injector pulse duration determines the quantity of fuel injected and is primarily determined
by engine load and speed. The ECM uses the input from the manifold absolute pressure sensor
and ignition pulses to output the required injector pulse duration from its memory. The injectors
are triggered via the power resistors, in staggered groups of six. Except during sudden throttle
opening, injector pulses occur every third ignition pulse (once per engine revolution).

FUEL INJECTION INPUTS

PRIMARY INPUTS CORRECTION INPUTS

ENGINE LOAD CRANKING

FUEL INJECTION ECM
ENGINE TEMPERATURE

AIR TEMPERATURE

ENGINE SPEED DEMAND

VOLTAGE

EMISSIONS
INJECTOR PULSE DURATION

T850/2.36

Correction inputs
Additional correction inputs are used by the ECM to vary injector pulse duration as necessary.

Cranking enrichment The ECM receives an input via the starter relay each time the engine is
started and increases the injector pulse duration during cranking to enrich the fuel mixture.

Engine warm-up correction During warm-up, the ECM lengthens the injector pulse duration
in response to the input received from the coolant temperature sensor.

Air density correction Intake air density is sensed by temperature measurement and supplied
to the ECM as an input. The ECM alters the injector pulse duration to lean or enrich the fuel flow
as necessary.

Demand corrections During acceleration and full power demands, the injector pulse duration
is lengthened by the ECM in response to input received from the throttle position sensor and two
full throttle switches. When sudden throttle opening is sensed, the ECM pulses all injectors once
to balance the rapid increase in air intake.

Voltage correction The system uses stabilized voltage for sensing and injector operation.

Emissions corrections “Closed loop” exhaust emissions control is provided by inputs from the two
heated oxygen sensors. At coolant temperatures below 95°F (35°C), air injection is applied to the
exhaust manifolds. During this period, inputs form the oxygen sensors are not used by the ECM.

29
5.3 Litre Engine Management 1989 – 90 Model Years

Engine Management System: Fuel Injection (continued)

FULL THROTTLE OPERATION

Full throttle operation
During full load operation, the engine must
FULL THROTTLE
produce maximum power. When activated by
MICRO SWITCH high manifold absolute pressure or full throttle
THROTTLE position (approximately 80% open), the full
TURNTABLE load switches provide a ground input to the
ECM.
FULL THROTTLE
VACUUM SWITCH
The full load switches are wires in parallel. At
INTAKE
AIR idle, both switches are open (the vacuum
switch is held open by manifold vacuum). As
the throttle is opened to full throttle, the
vacuum switch closes (low manifold vacuum)
and provides a ground input to the ECM. At
FUEL approximately 80% throttle opening, the micro
02 INJECTION
SENS. (2) ECM switch closes and provides a ground input to
the ECM.

EXHAUST The ECM enriches the fuel / air mixture by

lengthening the injector pulse duration and
T850/2.37
ignores the oxygen sensors feedback input.

Air injection
Secondary air is delivered to the exhaust manifolds during the initial engine warm-up period to
aid oxidation. The rotary vane air pump is belt driven from the crankshaft pulley. Air is delivered
to the exhaust manifolds via the air switching valve, which is controlled by a thermal vacuum
valve. The vacuum circuit also contains a delay valve.

At engine coolant temperatures below 95°F (35°C), the thermal vacuum valve opens. Manifold
vacuum is applied to the air switching valve, which in turn directs air injection to the exhaust ports.
The delay valve prevents vacuum loss to the air switching valve when the throttle is suddenly opened.

AIR INJECTION OPERATION

RIGHT
INTAKE MANIFOLD

DELAY VALVE

AIR
PUMP
AIR
THERMAL CLEANER
VACUUM
VALVE AIR
SWITCHING
VALVE
EXHAUST
PORTS

ENGINE COOLANT

T850/2.38

30
1989 – 90 Model Years 5.3 Litre Engine Management

Fuel Injection Components

Engine control module (ECM): Fuel injection 16CU ENGINE CONTROL MODULE: FUEL INJECTION
Location Trunk, right front.
Description The 16CU ECM contains an inte-
grated circuit for a dedicated fuel injection
control chip and an analog / digital converter for
the manifold pressure input. A manifold abso-
lute pressure sensor (transducer) is built into
the ECM. Fuel injection information is stored in
ROM (read only memory), so that for a given
combination of manifold pressure and engine
speed, the memory assigns a number propor-
tional to the required injector pulse duration.

Fuel injectors
Location Intake manifolds.
T850/2.39
Description Each fuel injector contains a
solenoid-operated needle valve, which is held
against a seat by spring pressure. When ener- FUEL INJECTOR
gized, the coil moves the needle away from
the seat, allowing pressurized fuel to flow
through the tip.

Full-load throttle switches

Location Vacuum: right of throttle turntable;
Micro: on throttle turntable pedestal.
Description The full-load switches provide a
ground input to the ECM during full-load con-
ditions.

T850/2.40

FULL LOAD SWITCHES

T850/2.41

31
5.3 Litre Engine Management 1989 – 92 Model Years

Engine Management System: Ignition — Overview

The ignition system is a digital microprocessor-controlled system that eliminates vacuum and
mechanical advance controls. The microprocessor memory contains ignition timing strategy with
precise timing for engine speeds, loads, and modes of operation. The microprocessor, in the ig-
nition ECM, receives inputs from engine sensors to program the necessary ignition timing. The
double-deck two-rotor distributor distributes the high tension voltage to A bank (right) via the
lower deck and to B bank (left) via the upper deck. The low-voltage circuit is switched by the
ignition ECM via the two power modules to the two ignition coils. High voltage is generated by
the ignition coils and supplied to the distributor.

The inputs supplied to the ECM from the engine sensors form two groups of control parameters:
primary inputs and correction inputs. The crankshaft position and engine-speed inputs are nec-
essary for the engine to start. The remaining inputs affect engine operation but are not necessary
for engine start.

Primary Inputs
• Crankshaft position — TDC sensor
• Engine speed — Engine speed (flywheel) sensor
• Engine load — Manifold absolute pressure sensor

Correction Inputs
• Throttle position — Idle switch
• Engine coolant temperature — Coolant temperature sensor
• Intake air temperature — Air temperature switch

NOTE: The sensors and switches are unique to the digital ignition system and are not used or
shared by the fuel injection system.

32
 B
1989 – 92 Model Years

BANK B BANK A IDLE IGNITION COILS

(LEFT) (RIGHT) SWITCH

AIR POWER
TEMPERATURE MODULES A B
SWITCH

COOLANT
TEMP.
SENS.
ENGINE
SPEED
5.3 LITRE V12 ENGINE MANAGEMENT SYSTEM: IGNITION (1989 – 92 MY)

TDC
SENSOR
SENSOR

IGNITION ECM

MAN. ABSOLUTE
PRESSURE SENS.

BATTERY
VOLTAGE

IGNITION
SWITCH

T850/2.42

33
5.3 Litre Engine Management
5.3 Litre Engine Management 1989 – 92 Model Years

Ignition: Engine Operating Modes

ALL OPERATING MODES

All operating modes
During all engine operating modes, the crank-
shaft position sensor (TDC sensor) input is
used by the ECM to program spark delivery.
IGNITION ECM Crankshaft position is referenced from A bank.
The ECM programs spark delivery for both
banks from the A bank reference.
CRANKSHAFT
POSITION (TDC)
Engine starting
Ignition timing during cranking and start-up is
programmed by engine speed and coolant
temperature. Engine speed is obtained from
the engine speed (flywheel) sensor; engine
coolant temperature is obtained from the
T850/2.43 coolant temperature sensor.

ENGINE STARTING

CRANKSHAFT IGNITION ECM

POSITION

ENGINE SPEED

COOLANT TEMP. IGNITION TIMING

T850/2.44

34
1989 – 92 Model Years 5.3 Litre Engine Management

Closed throttle running CLOSED THROTTLE RUNNING

Ignition timing during closed throttle operation
is programmed separately for idle and decel-
eration. Closed throttle running is controlled
by the idle switch and is programmed by en- IDLE SWITCH IGNITION ECM
gine speed and coolant temperature.
CRANKSHAFT
POSITION
When the idle switch is closed, the ECM does
not recognize the engine load (manifold absolute ENGINE SPEED
pressure sensor) input and uses the idle portion
IGNITION TIMING
of the ignition strategy for ignition timing. COOLANT TEMP.

Engine speed is obtained from the engine

speed (flywheel) sensor; engine coolant tem-
perature is obtained from the coolant
temperature sensor.

Open throttle running

Ignition timing during open throttle running is
programmed by primary inputs from engine T850/2.45

speed and engine load and from correction

inputs from coolant temperature and intake air
temperature.

Engine speed is obtained from the engine speed (flywheel) sensor; engine load is obtained from the
manifold absolute pressure sensor; engine coolant temperature is obtained from the coolant tempera-
ture sensor; intake air temperature information is obtained from the intake air temperature switch.

OPEN THROTTLE RUNNING

PRIMARY INPUTS CORRECTION INPUTS

ENGINE LOAD IGNITION ECM

COOLANT TEMP.

ENGINE SPEED

INTAKE AIR
TEMP.
CRANKSHAFT
IGNITION TIMING
POSITION

T850/2.46

35
36
COIL B
AIR TEMPERATURE (YELLOW IDENT)
COOLANT TEMPERATURE SWITCH
SENSOR

(1992 MY)
(THROUGH 1991 MY)

POWER MODULE A
DIGITAL IGNITION SYSTEM COMPONENT LOCATIONS
5.3 Litre Engine Management

DISTRIBUTOR

POWER MODULE B

ECM
(ON RIGHT ‘A’ POST
TRIM PANEL)

TDC SENSOR IDLE SWITCH

ENGINE SPEED
SENSOR
COIL A
(RED IDENT)

T850/2.47
1989 – 92 Model Years
1989 – 92 Model Years 5.3 Litre Engine Management

Ignition Components

Engine control module (ECM): Ignition ENGINE CONTROL MODULE: IGNITION

Location Front passenger footwell, ‘A’ post
trim panel.
Description The ECM contains the micropro-
cessor for receiving analog inputs from the
engine sensors and programming the ignition
timing, which is accessed and delivered from
the ignition strategy stored in the memory. In-
tegral in the ECM is the manifold absolute
pressure sensor.

Top dead-center sensor

Location Front crankshaft pulley.
Description The sensor is triggered by a
three-toothed reluctor to produce a TDC refer-
T850/2.48
ence for A bank.

Engine speed sensor TOP DEAD-CENTER SENSOR

Location Flywheel ring gear.
Description The sensor is triggered by the
flywheel ring gear teeth, which act as a
reluctor to produce an engine speed input to
the ECM.

RESISTANCE: 700 – 800 OHMS

T850/2.49

ENGINE SPEED SENSOR

RESISTANCE: 700 – 800 OHMS

T850/2.50

37
5.3 Litre Engine Management 1989 – 92 Model Years

Ignition Components (continued)

COOLANT TEMPERATURE SENSOR

Coolant temperature sensor
Location Right cylinder head coolant rail,
front.
Description The coolant temperature sensor
is a temperature-sensitive resistor. As the
coolant temperature rises, the electrical resis-
tance decreases providing a coolant
temperature input to the ECM.

Idle switch
Location Left throttle linkage bellcrank.
Description The micro switch closes when
the throttle is closed, signaling the ECM that
the engine is at idle or decelerating.

T850/2.51
Air temperature sensor
Location Right air cleaner back plate.
IDLE SWITCH Description The bimetal switch closes at
167°F (75°C) to signal the ECM to retard the
ignition timing at high intake air temperature.

T850/2.52

AIR TEMPERATURE SENSOR

T850/2.53

38
1989 – 92 Model Years 5.3 Litre Engine Management

Power modules POWER MODULE

Location Upper radiator support.
Description The power modules switch the
low voltage circuit to ground when signaled by
the ECM.

Ignition coils
Location Engine vee: A bank – red ident on
harness plug; B bank – yellow ident on har-
ness plug.
Description The ignition coils generate high
voltage current for distribution to the spark
plugs.

Distributor
T850/2.54
Location Engine vee.
Description The distributor is a double-deck
design with the upper rotor distributing high IGNITION COIL
voltage current to B bank spark plugs and the
lower rotor distributing high voltage current to
A bank spark plugs.

T850/2.55

DISTRIBUTOR

T850/2.56

39
The following Figures and Data pages are extracted from select
Electrical Guides and are included here as an
aid to understanding the Engine Management system.
Do not use this information to diagnose vehicle faults.

Always refer to the Model and Model Year specific

Electrical Guide for accurate information.
 XJR-S 6.0 Litre Engine Management

Contents

System Introduction 2

Crankcase Emission Control 3

Engine Management System Overview 4–5

Fuel Delivery and Evaporative Emission Control 6–7

Fuel Injection 8–9

Ignition 10 – 11

Additional ECM Functions 12 – 13

On-Board Diagnostics System 14 – 15

Engine Management System Components 16 – 17

Engine Management System Service Aid 18 – 25

1
XJR-S 6.0 Litre Engine Management

System Introduction

The XJR-S is a specialized Jaguar model that uses a 6.0 litre version of the basic 5.3 litre V12
engine. A Zytek engine management system that integrates sequential fuel injection, ignition and
emission control is used to provide ultra high performance.

Engine Specifications
Displacement 5993 cc
Bore / stroke 90 mm x 78.5 mm
Compression ratio 11.0:1
Power (DIN) 318 hp @ 5200 rpm
Torque (DIN) 339 ft lbs @ 3750 rpm
Spark plugs Champion RS6 YCC 0.025 in gap
Fuel requirement Unleaded gasoline — 95 RON octane rating
Idle speed 750 rpm — N or P

2
 XJR-S 6.0 Litre Engine Management

Crankcase Emission Control

Crankcase ventilation
The 5.3 litre crankcase ventilation system is retained. Piston blowby gases are scavenged from
the crankcase and the camshaft housings via the left timing housing and the camshaft covers.
The gases are collected and fed into the engine through the left air cleaner.

XJR-S 6.0 LITRE V12 CRANKCASE EMISSION CONTROL

PCV VALVE

T850/3.01

3
XJR-S 6.0 Litre Engine Management

Engine Management System Overview

The Zytek engine management system is a microprocessor based system with control over fuel
delivery, evaporative emission purging, sequential fuel injection, exhaust emission, ignition tim-
ing and air injection. A single engine control module incorporating a manifold absolute pressure
sensor drives the various functions by applying inputs received from engine sensors with the
strategies stored in memory. The ECM contains an on-board diagnostic capability that can be
accessed via serial communication through a lap top computer using special software.

The complete list of engine management ECM functions is as follows:

• Fuel delivery • Engine speed limitation
• Evaporative emission canister purging • Ignition timing
• Sequential fuel injection – idle, acceleration, • Air conditioning compressor override
cruise, deceleration (high engine temperature)
• Cold start • Engine speed output signal (tachometer)
• Warm-up • Fuel monitoring (trip computer)
• Closed loop exhaust emission control • On-board diagnostics (OBD)
• Air injection control • CHECK ENGINE warning and diagnostic
• Wide open throttle injector disable trouble codes
on cranking • Limp home capability
• Overrun fuel cutoff • Serial communication

XJR-S ENGINE MANAGEMENT COMPO-

NENTS
CONNECTOR JSC12
IGNITION COIL

FUEL TEMPERATURE
SENSOR

AIR INJECTION COOLANT

SOLENOID VACUUM TEMPERATURE
VALVE SENSOR

INTAKE AIR
INTAKE AIR TEMPERATURE
TEMPERATURE SENSOR
SENSOR

POWER
RESISTORS

IGNITION AMPLIFIER
T850/3.02

4
 FUEL PUMP
RELAY

FUEL PRESSURE
REGULATOR
THROTTLE POSITION
FUEL TANK SENSOR

FILTER ECM ECM

FUEL RAIL
FUEL TEMP. INTAKE AIR TEMP.
SENSOR SENSORS (2)
INJECTOR ECM
ECM
INTAKE AIR
ECM
XJR-S ENGINE MANAGEMENT SYSTEM

COOLANT TEMP. SENSOR AIR INJ.

PUMP

IGNITION
COIL
DISTRIBUTOR ECM
OXYGEN
SENSORS (2)
EXTRA
IGNITION AIR VALVE
AMPLIFIER
PULSE DAMPER
EXHAUST
ECM AIR INJECTION PUMP
MANIFOLD
ABSOLUTE
PRESSURE PURGE VALVES
SYNCHRONIZATION SENSOR
AND ENGINE SPEED A/C CLUTCH OVERRIDE
ECM COOLANT TEMP. SENSOR
(SYNCHRONIZATION
AND ENGINE SPEED) EMS
FUEL TEMP. SENSOR MAIN
ECM RELAY INERTIA IGNITION
THROTTLE POSITION SENSOR SWITCH SWITCH
INTAKE AIR TEMP. SENSORS
FUEL PUMP
OXYGEN SENSORS FUEL FUSE
PUMP FUEL PUMP
IGNITION TIMING RELAY
OXYGEN
INJECTORS SENSOR
OXYGEN SENSOR HEATERS
HEATERS FUSE
POWER RESISTORS CHECK ENGINE WARNING
INJECTORS
DIAGNOSTIC TROUBLE CODES

SERIAL COMMUNICATIONS
POWER RESISTORS

T850/3.03

5
XJR-S 6.0 Litre Engine Management
XJR-S 6.0 Litre Engine Management

Fuel Delivery and Evaporative Emission Control

Fuel delivery
XJR-S FUEL PUMPS
The basic fuel delivery system is unchanged
from the 1992 model year XJS V12 vehicles. In
order to meet the demands of the 6 litre
engine, two downrated versions of the stan-
dard fuel pump modules are used. These must
be replaced as a matched pair. The fuel pumps
are activated by the ECM (electronic control
module) only when engine cranking or engine
speed signals are received. Two vertical black
stripes identify the twin fuel pump tank.

Evaporative emission control

The evaporative emission control system uses
the same canister and vacuum / pressure relief
valve as the 1992 model year XJS V12 vehicle,
however, the canister is inverted. Engine run-
on is prevented by a normally closed purge
T850/3.04
shut-off valve. The valve opens when the igni-
tion is switch ON. Canister purging is
controlled by the ECM via two purge control valves in the purge lines to the left and right intake
manifolds. The ECM opens the valves simultaneously according to an engine load and speed
strategy. Correct functioning of the purge shut-off valve and the purge control valves is moni-
tored by the on-board diagnostic system in the ECM.

XJR-S EVAPORATIVE EMISSION CONTROL SYSTEM

CANISTER SHOWN UPSIDE DOWN

PURGE
VALVES

PURGE
SHUT-OFF VALVE

VACUUM / PRESSURE
RELIEF VALVE

T850/3.05

6
 ROLL-OVER VALVE PRESSURE FUEL RAIL
EVAPORATIVE RELIEF VALVE
FLANGE
FUEL INJ.
INTAKE INTAKE
MANIFOLD MANIFOLD

RETURN FUEL
FUEL FILTERS PRES.
PUMPS REG.
PUMP
INLET FILTERS
FILTERS
VENT
FUEL TANK FUEL PUMP FUEL PUMP
MODULE MODULE
FILTER
XJR-S FUEL DELIVERY AND EVAPORATIVE EMISSION CONTROL SYSTEM

PURGE
VALVES
PURGE
SHUT-OFF VALVE

VACUUM / PRESSURE
RELIEF VALVE
(ROCHESTER VALVE)
ENGINE ENGINE LOAD
MANAGEMENT
ECM
ENGINE SPEED

CHARCOAL IGNITION SWITCHED

CANISTER POWER SUPPLY

T850/3.06

7
XJR-S 6.0 Litre Engine Management
XJR-S 6.0 Litre Engine Management

Fuel Injection

XJR-S FUEL INJECTION CONTROL

Fuel metering control
Fuel metering is obtained by controlling the
injector pulse duration during each engine
cycle (two crankshaft rotations). The pulse
duration is varied by the engine control module
ENGINE CONTROL MODULE (ECM) according to several sensor inputs. The
sensed control inputs form two groups — pri-
mary and secondary. Primary control inputs
MANIFOLD are intake manifold absolute pressure (MAP)
ABSOLUTE PRESSURE
PRESSURE TRANSDUCER and engine speed; secondary control inputs
(ENGINE LOAD) consist of engine coolant temperature, intake
air temperature, throttle movement and posi-
tion, exhaust oxygen content, crankshaft
position, cranking signal, fuel temperature and
MANIFOLD PRESSURE battery voltage. The injectors are pulsed
ENGINE SPEED V
ENGINE SPEED sequentially, once per engine cycle in the
engine firing order.

Primary control
Fuel metering is controlled primarily as a func-
tion of intake manifold absolute pressure
ENGINE MOVING
COOLANT TEMP. THROTTLE (MAP) and engine speed. Manifold pressure
INTAKE AIR CORRECTION TRIMS CLOSED OR is sensed by a pressure transducer located in
TEMP. FACTORS WIDE-OPEN
THROTTLE the engine control module and connected to
CRANKING EXHAUST OXYGEN the A bank manifold by a vacuum line. Engine
CONTENT speed is sensed by a reluctor mounted in the
FEEDBACK
ignition distributor. In addition to engine
speed, the Hall effect reluctor supplies a syn-
chronization input to the ECM for fuel injection
BATTERY VOLTAGE BATTERY timing.
CORRECTION VOLTAGE

Fueling strategies are held in memory

(EPROM) in the ECM and form a manifold
pressure v engine speed matrix. Injector pulse
INJECTOR PULSE duration is then calculated according to sec-
DURATION ondary correction factors and trims. The
resulting injector pulse duration is further
modified to account for battery voltage.

SYNCHRONIZATION INJECTOR
TIMING

INJECTOR(S)

T850/3.07

8
 XJR-S 6.0 Litre Engine Management

Secondary control
Secondary fueling enrichment is provided for engine starting, warm-up and throttle response at
all temperatures within the engine’s operating range.

Coolant temperature The coolant temperature sensor provides an electrical input to the ECM.
During engine starting and warm-up, enrichment is provided by increasing the injector pulse
duration when coolant temperature is below normal operating temperature. Enrichment is re-
duced with increasing engine speed and load.

Engine starting When the engine starts at low temperatures, the ECM pulses all injectors
together, six injections per engine cycle (2 crankshaft revolutions). Normal sequential timing of
the injectors is resumed after a preset number of injections.

After start enrichment After engine start-up, the ECM increases the injector pulse duration
above the normal running requirement and then decreases the pulse duration at a fixed rate over
a preset number of engine revolutions.

Throttle movement and position The throttle position sensor provides electrical signals to the
ECM for opened and closed throttle operation as well as throttle movement during acceleration
and deceleration.

Intake air temperature Fuel metering is adjusted to vary approximately with the density of the
engine intake air. Intake air density is sensed by measuring the air temperature at both the left
and right air intakes. Independent correction is provided for each cylinder bank.

Full load Full load fuel metering varies with throttle position and engine speed. Under full load
conditions, exhaust oxygen sensor closed loop control is disabled.

Idle fuel To compensate for variable injector flow at short pulse durations, the ECM has an
adjustable idle trim function to optimize the idle fuel metering for each cylinder bank. Adjust-
ments are made using a lap-top computer with special software.

Fuel temperature To improve hot starting and running at high ambient temperature, additional
fuel is supplied as a function of fuel temperature. A fuel temperature sensor on the fuel rail pro-
vides an input to the ECM.

Air / fuel ratio (closed loop control) In order to achieve optimum performance from the ex-
haust three-way catalyst system, the exhaust oxygen content is monitored and controlled by
trimming the fuel metering. Two oxygen sensors are used–one in each exhaust down pipe, after
the primary catalyst. Closed loop control is disabled under these conditions:

• during engine warm-up when the air injection is operating

• following hot starts until the oxygen sensors reach operating temperature
• during full load operation
• during deceleration fuel cutoff (engine overrun).

Battery voltage The time necessary for full injector open and close to occur varies with battery
voltage. For example, with low battery voltage, the time necessary for full injector open to oc-
cur is long; therefore, less fuel is delivered for a given pulse duration. The opposite is true for high
battery voltage. The ECM corrects the injector pulse duration to achieve the fuel delivery that
would be obtained at a nominal reference voltage.

9
XJR-S 6.0 Litre Engine Management

Ignition

IGNITION: STARTING Ignition timing control

The ignition timing is varied by the ECM
ENGINE CONTROL MODULE according to several sensor inputs. The
sensed control inputs form two groups – pri-
mary and secondary. Primary control inputs
PRESSURE are intake manifold absolute pressure and
TRANSDUCER engine speed; secondary control inputs con-
sist of engine coolant temperature, intake air
temperature and throttle position. Crankshaft
position is determined by the Hall effect
reluctor (synchronization sensor) in the dis-
FIXED
ENGINE SPEED STARTING IGNITION tributor.
(CRANKING) TIMING

Ignition timing strategies are held in memory

(EPROM) in the ECM. The ECM uses second-
ary sensor inputs to determine the engine
operating condition — starting, closed throttle
SYNCHRONIZATION IGNITION operation or open throttle operation — and
TIMING
then applies the correct ignition timing.

Engine starting During engine cranking, the

ignition timing is fixed by the ECM. After start-
ing, the ignition timing is varied as determined
by an idle strategy.
IGNITION AMPLIFIER
T850/3.08
Idle A separate “short” idle strategy that
ensures steady idle is employed when the
vehicle is stationary and the throttle closed.
IGNITION: CLOSED THROTTLE
The input from the road speed sensor is used
ENGINE CONTROL MODULE to determine whether the vehicle is in motion
or stationary. Closed throttle operation is
sensed from the throttle position sensor. The
PRESSURE
engine speed change-over points between
TRANSDUCER starting and idle are written in the ECM
memory.
VEHICLE
STATIONARY

THROTTLE POSITION

ENGINE SPEED IGNITION

IDLE STRATEGY
ENGINE
COOLANT TEMP.

IGNITION
SYNCHRONIZATION
TIMING

IGNITION AMPLIFIER

T850/3.09

10
 XJR-S 6.0 Litre Engine Management

Open throttle operation For any given mani- IGNITION: OPEN THROTTLE
fold absolute pressure (MAP) and engine
speed, the ECM will determine the required
ignition timing from the “lookup” table. The ENGINE CONTROL MODULE

timing is then corrected for engine tempera-

ture, intake air temperature and for acceleration.
MANIFOLD
ABSOLUTE PRESSURE
PRESSURE TRANSDUCER
(ENGINE LOAD)

IGNITION
ENGINE SPEED STRATEGY

ENGINE
COOLANT
TEMP. CORRECTION
FACTORS
INTAKE AIR
TEMP.

THROTTLE
POSITION ACCELERATION
SENSOR CORRECTION
(THROTTLE
MOVEMENT)

IGNITION
SYNCHRONIZATION TIMING

IGNITION AMPLIFIER

T850/3.10

11
XJR-S 6.0 Litre Engine Management

Additional ECM functions

Additional ECM functions include air injection control, fuel cutoff and air conditioning compres-
sor clutch override.

Air injection Air injection is enabled by the ECM during engine warm-up. The ECM activates
the solenoid vacuum valve to apply intake manifold vacuum to the air switching valve to switch
air delivery to the exhaust ports. When the coolant temperature reaches 125°F, the ECM
switches off the vacuum valve causing the air delivery to be switched from the exhaust ports
back to the right air cleaner. The air switching valve, solenoid vacuum valve and delay valve are
carry-over components from the 1992 model year XJS V12.

AIR INJECTION OPERATION

ENGINE
MANAGEMENT

ECM
ENGINE TEMPERATURE

RIGHT
INTAKE MANIFOLD

IGNITION

AIR
SOLENOID AIR PUMP
DELAY VALVE
VACUUM VALVE CLEANER

EXHAUST
PORTS
AIR SWITCHING
VALVE

T850/3.11

12
 XJR-S 6.0 Litre Engine Management

Fuel cutoff Fuel cutoff is used during engine overrun conditions, for engine overspeed protec-
tion, and for flooding protection during wide-open-throttle start. The following table lists the fuel
cutoff conditions and control specifications:

Controlled parameter Fuel cutoff (engine speed) Reinstate

Engine overrun (deceleration) 1395 plus rpm (engine temp. 930 rpm
above 60°C, throttle position below
threshold level, vehicle in motion)

Engine overspeed 6498 rpm 6494 rpm

Wide-open-throttle start Engine cranking Throttle closed

NOTE: The ECM uses the road speed input to determine “vehicle in motion” when applying
deceleration fuel cutoff.

Air conditioner compressor clutch override The ECM switches the compressor clutch relay
coil ground circuit to override the compressor operation if the engine coolant temperature reaches
257°F (125°C) or higher. Compressor operation is reinstated when the temperature drops to
253°F (123°C).

Idle speed control

Idle speed control is maintained solely by the adjustable idle air bleed at the extra air valve. No
supplementary air valve or electronic idle speed control is provided.

13
XJR-S 6.0 Litre Engine Management

On-Board Diagnostics System (OBD)

The ECM includes a fault diagnosis facility that continuously monitors the operation of the engine
management sensors and components. If a fault is detected, the OBD system will activate the
CHECK ENGINE warning in the instrument pack and on the trip computer display. In addition, it
will flag a diagnostic trouble code (DTC) in the ECM memory. The ECM can, at any time, be
interrogated through the trip computer display by switching off the ignition then switching on the
ignition. The CHECK ENGINE warning will display and the DTC will appear 5 seconds later. If
two or more DTCs are flagged in memory, only the highest priority code will be displayed. The
remaining codes will be displayed, in turn, as the faults are corrected and erased from memory.

NOTE: Fueling diagnostics are disabled when the fuel tank level falls below approximately 6.5
gallons (25 litres).

Serial communications
Serial communications between the engine management system and a lap top diagnostic com-
puter are available via the EMS data link connector (PM 4) located in the passenger’s footwell.
Serial communication is used for engine setup, fault diagnosis and erasing diagnostic trouble
codes.

Limp home mode

In order to allow vehicle operation if a malfunction occurs, “limp home” default strategies are
incorporated as an ECM facility. The ECM will substitute a nominal value for missing inputs from
various sensors and components.

Open loop default

Certain malfunctions have “open loop” default when in limp home mode. If a malfunction has
open loop default, oxygen sensor inputs are ignored. If a malfunction does not have open loop
default, oxygen sensor inputs are used.

14
 XJR-S 6.0 Litre Engine Management

Diagnostic trouble codes

The available DTCs are listed in order of priority on the following table. Limp home and/or open
loop default are available as indicated.

DTC Limp Home Open Loop Input or Component Checked

Default Default
29 ECM Self-test
55 X X Engine ground sensing circuit
44 X X Oxygen sensor circuit — A bank
45 X X Oxygen sensor circuit — B bank
18 Fuel metering above idle — A bank
19 Fuel metering above idle — B bank
12 Engine speed and synchronization sensors circuit
24 Ignition drive circuit
36 X X Injector electrical circuit — Injector 1A
56 X X Injector electrical circuit — Injector 2A
46 X X Injector electrical circuit — Injector 3A
58 X X Injector electrical circuit — Injector 4A
38 X X Injector electrical circuit — Injector 5A
48 X X Injector electrical circuit — Injector 6A
49 X X Injector electrical circuit — Injector 1B
39 X X Injector electrical circuit — Injector 2B
59 X X Injector electrical circuit — Injector 3B
47 X X Injector electrical circuit — Injector 4B
57 X X Injector electrical circuit — Injector 5B
37 X X Injector electrical circuit — Injector 6B
34 X X Injector drive circuit
33 X X Fuel metering at idle — A bank
35 X X Fuel metering at idle — B bank
23 Fuel metering at idle — A and B banks combined
13 X Pressure transducer and sensing hose
17 X Throttle position sensor circuit
11 X Pressure transducer / throttle position sensor circuit
27 X Sensor ground circuit (coolant, intake air, fuel temp.)
14 X Coolant temperature sensor circuit
15 X Intake air temperature sensor circuit — A bank
16 X Intake air temperature sensor circuit — B bank
26 X Intake air temperature sensor circuits —
excessive difference, A bank to B bank
25 X Fuel temperature sensor circuit
22 Fuel pump relay control circuit
88 Purge valves circuit
79 Purge shut-off valve circuit
66 X X Air injection solenoid vacuum valve circuit
68 X Road speed sensor circuit

15
XJR-S 6.0 Litre Engine Management

Engine Management Components

Engine control module Fuel injectors

Location Passenger’s side ‘A’ post Location Fuel rail / intake manifolds
Description The ECM is a microprocessor Description The fuel injectors are carry-
based unit with control over fuel injection, emis- over components from the 1992 model
sion control and ignition The ECM contains an year XJS V12.
integral pressure transducer for sensing engine
manifold absolute pressure. A vacuum line runs Power resistors
from the right intake manifold to the ECM Location Engine compartment, right front
through a damper. The vacuum line is routed
Description Twin power resistor packs con-
behind the passenger’s ‘A’ post trim. The
tain a resistor for each injector.
damper is located above the passenger footwell.
Throttle position sensor
ENGINE CONTROL MODULE Location Under the throttle turntable
Description The throttle position sensor is a
carry-over component from the 1992 model
year XJS V12.

Coolant temperature sensor

Location Left thermostat housing
Description The coolant temperature sensor
is a carry-over component from the 1992
model year XJS V12.

Intake air temperature sensors

Location Right and left air cleaner intakes
Description Two intake air temperature sensors
are used. The sensors are carry-over components
from the 1992 model year XJS V12.

Fuel temperature sensor

Location Fuel rail, right
Description The fuel temperature sensor is a
T850/3.12 temperature sensitive resistor (thermistor). As
the fuel temperature rises, the electrical resis-
tance decreases providing a fuel temperature
input to the ECM.

Oxygen sensors
Location Exhaust down pipes
Description The oxygen sensors are carry-
over components from the 1992 model year
XJS V12.

16
 XJR-S 6.0 Litre Engine Management

Extra air valve Purge shut-off valve

Location Left cylinder head, rear Location Charcoal canister
Description The extra air valve is carry- Description The purge shut-off valve is a so-
over component from the 1992 model lenoid-operated vacuum switching valve
year XJS V12. identical to the supplementary air valve used in
the 1992 model year XJS V12.
Inertia switch
Location Passenger’s side A post Ignition amplifier
Description The inertia switch is carry- Location Radiator support, top
over component from the 1992 model Description The electronic ignition amplifier
year XJS V12. performs primary circuit switching as signaled
by the ECM.
Air injection solenoid vacuum valve
Location Right cylinder head, front Ignition coil
Description The solenoid vacuum valve is Location Engine vee
carry-over component from the 1992 model Description The ignition coil generates high
year XJS V12. voltage current for distribution to the spark
plugs.
Air switching valve
Location Engine, right front Ignition distributor
Description The air switching valve is carry- Location Engine vee
over component from the 1992 model year Description The distributor is a single deck
XJS V12. design incorporating sensors for engine
speed and crankshaft position. Engine speed
Purge valves output is derived from a Hall effect twelve
Location Charcoal canister segment reluctor. The reluctor has an inte-
gral inner one segment rotor that generates a
Description The purge valves are solenoid-
crankshaft position output for synchronization
operated vacuum switching valves identical to
of the sequential fuel injection.
the purge valve used in the AJ6 4.0L engine
installation.

17
XJR-S 6.0 Litre Engine Management

Engine Management System Service Aid

Zytek Systems, the supplier of the XJR-S engine management system have developed a com-
puterized engine management service aid consisting of special software run on a standard
portable lap-top computer with custom connection to the engine management system. The
Zytek service aid allows monitoring of the system under both static and dynamic conditions.

Main menu options

The main menu options are outlined here. Com-
plete information is contained in the XJR-S
Product Support Manual.

DYNAMIC DISPLAY OF SYSTEM PARAMETERS Dynamic display of system parameters

This option presents a visual display of the en-
COOLANT TEMPERATURE : 193 Deg. F AIR TEMPERATURE-BANK A : 123 Deg. F
gine inputs monitored by the ECM, and the
FUEL TEMPERATURE : 119 Deg. F AIR TEMPERATURE-BANK B : 143 Deg. F outputs for engine operation from the ECM.
The values will be generated with the engine
ENGINE SPEED : 780 RPM THROTTLE POSITION : 323 mV off or running; however, the ignition must be
ROAD SPEED : 0 MPH MANIFOLD DEPRESSION : 13.1 InHg ON for the computer to assemble the informa-
tion. An expanded explanation of the values
BATTERY VOLTAGE : 13.9 V PURGE VALVE VOLTAGE: 11.1 V AIR PUMP: DISABLED and their interpretation is given on pages
FUEL TANK VOLTAGE: 11.0 V AIR COND : ENABLED PURGE FLOW : 2 % 20 – 23. Press <Q> to return to the main
menu.
LAMBDA A VOLTS: 0.75 V LAMBDA B VOLTS: 0.39 V INJECTOR OPEN TIME : 4.47 mS

LAMBDA GROUND VOLTS: 0.45 V IGNITION ADVANCE : 3.4 Deg

DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu

T850/3.14

DIAGNOSTICS
Diagnostics This option is used only to access
FAULT CODE ANALYSIS and erase Diagnostic Trouble Codes flagged in
Total number of Faults found is 1 the ECM memory. No computerized diagnos-
Code Fault
tic routines are provided. Press <Q> to return
15 AIR THERMISTOR / WIRING -A BANK to the main menu.

DELETE FAULT CODE

WARNING! Only delete if the fault has been rectified!

Delete #15,AIR THERMISTOR / WIRING -A BANK. Are You Sure (Y/N)

<D>-Delete Fault <t PgDn PgUp> -Select Fault <Q>-Quit

T850/3.15

18
 XJR-S 6.0 Litre Engine Management

CLOSED LOOP CONTROL DATA

Closed loop control data This option dis- BANK A

% of Lower Clamp
plays the ECM closed loop fuel metering
control in the form of bar graphs for A and B
-100 -80 -60 -40 -20 0 20 40 60 80 100
banks. In addition, the throttle opening is rep- BANK A fueling : 100% BANK A idle trim : 10.0%
resented as a percent (0 = closed; 100 = wide
BANK B
open). An expanded explanation of the values % of Lower Clamp
and their interpretation is given on page 23.
Press <Q> to return to the main menu. -100 -80 -60 -40 -20 0 20 40 60 80 100
BANK B fueling : 100% BANK B idle trim : -4.2%

THROTTLE:- 303 mV

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Feedback Data. <Q> or <Esc>-Qu it

T850/3.16

DISPLAY PROGRAM AND DATA IDENTIFICATION DETAILS

Display program and data identification Program /data currently in engine control unit:-
details This option provides the identification
of the software program within the ECM.
Switch the ignition ON (do not start the
Program Identification : EMO00004 CS 6- 7-92
engine) and press <ENTER>. The computer
will display the program data. Press <Q> to
return to the main menu.
Data Identification : JSFEDL93 CA 17- 6-92

Additional information : -

1993 MODEL YEAR, FEDERAL SPECIFICATION, PRODUCTION DATA-LISTING

DISPLAY IDENTIFICATION DETAILS Press <Q> to quit

T850/3.17

SET UP ENGINE

Set up engine This option provides a step-by- Before proceeding with the engine set-up function, ensure that the following
conditions have been met.
step procedure for engine set up using the
computer screen displays. It is not necessary to
complete the procedures in sequence as each 1). Turn the engine OFF.

procedure can be accessed independently. 2). Set the gear selector to PARK or NEUTRAL.
Press <SPACE> to cycle to the next procedure.
3). Turn the air conditioning unit OFF.
An expanded explanation of the procedures is
given on pages 24 – 25. Press <Q> or <ES- 4). Ensure Ignition is off, connect to timing light, then turn ignition on.
CAPE> to return to the main menu.
5). Be sure that there are no diagnostic faults outstanding.

IMPORTANT: Under normal circum-

stances, the engine set up procedures
should only be carried out after component
replacement or engine disassembly and
1). Set up engine. <Q> or <Esc> quits, <SPACE> cycles to next page
reassembly.
T850/3.18

19
XJR-S 6.0 Litre Engine Management

Dynamic Display of System Parameters

IGNITION ON; ENGINE STOPPED / COLD (AMBIENT) By selecting this option from the main menu,
the engine inputs monitored by the ECM, and
COOLANT TEMPERATURE : 68 Deg. F AIR TEMPERATURE-BANK A : 73 Deg. F the outputs for engine operation from the
FUEL TEMPERATURE : 71 Deg. F AIR TEMPERATURE-BANK B : 72 Deg. F ECM will be displayed. The values will be gen-
erated with the engine off or running;
ENGINE SPEED : STOPPED THROTTLE POSITION : 303 mV however, the ignition must be ON for the
ROAD SPEED : 0 MPH MANIFOLD DEPRESSION : 30.3 InHg
computer to assemble the information. The
information provided in this sub section ex-
BATTERY VOLTAGE : 12.1 V PURGE VALVE VOLTAGE: 9.3 V AIR PUMP: DISABLED plains each value and adds additional detail as
necessary to the understanding of the value
FUEL TANK VOLTAGE: 9.5 V AIR COND : ENABLED PURGE FLOW : 0 %
displayed.
LAMBDA A VOLTS: 4.71 V LAMBDA B VOLTS: 4.80 V INJECTOR OPEN TIME : 65.54mS
Coolant, air and fuel temperatures
LAMBDA GROUND VOLTS: 0.47 V IGNITION ADVANCE : 0.0 Deg
The upper box displays coolant temperature, A
bank air temperature, B bank air temperature
and fuel temperature as input to the ECM
DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu
from the respective sensors. Sensor tempera-
T850/3.19 ture is expressed in degrees Fahrenheit. The
ENGINE AFTER-START WARM UP sensor temperatures will be displayed in one
of three possible ways:
COOLANT TEMPERATURE : 75 Deg. F AIR TEMPERATURE-BANK A : 72 Deg. F
• Actual temperature in degrees Fahrenheit
FUEL TEMPERATURE : 71 Deg. F AIR TEMPERATURE-BANK B : 70 Deg. F
• “Short circuit” indicating a short circuit
within the sensor or the sensor circuit.
ENGINE SPEED : 880 RPM THROTTLE POSITION : 303 mV
• “Open circuit” indicating an open circuit
ROAD SPEED : 0 MPH MANIFOLD DEPRESSION : 17.8 InHg
within the sensor or the sensor circuit
BATTERY VOLTAGE : 14.4 V PURGE VALVE VOLTAGE: 11.2 V AIR PUMP: ENABLED
Engine speed
FUEL TANK VOLTAGE: 11.3 V AIR COND : ENABLED PURGE FLOW : 0 % Engine speed is expressed in rpm (revolutions
per minute). The screen displayed value rep-
LAMBDA A VOLTS: 0.33 V LAMBDA B VOLTS: 1.02 V INJECTOR OPEN TIME : 7.90mS
resents the actual engine speed sensed by the
LAMBDA GROUND VOLTS: 0.43 V IGNITION ADVANCE : 0.0 Deg ECM from the engine speed sensor.

If “stopped” is displayed during cranking, the

DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu ECM is not receiving an engine speed input
T850/3.20 from the speed sensor.
ENGINE AT IDLE / NORMAL TEMPERATURE
Throttle position
COOLANT TEMPERATURE : 193 Deg. F AIR TEMPERATURE-BANK A : 123 Deg. F Throttle opening is expressed as a voltage on a
scale of 0 to 5000 mVolts. The throttle position
FUEL TEMPERATURE : 119 Deg. F AIR TEMPERATURE-BANK B : 143 Deg. F
sensor input to the ECM can be observed with
the engine stopped and the ignition on. Closed
ENGINE SPEED : 780 RPM THROTTLE POSITION : 323 mV
throttle (idle) should indicate very low voltage.
ROAD SPEED : 0 MPH MANIFOLD DEPRESSION : 13.1 InHg As the throttle is opened, the voltage should
rise smoothly. When held full open, the voltage
BATTERY VOLTAGE : 13.9 V PURGE VALVE VOLTAGE: 11.1 V AIR PUMP: DISABLED
should be high and steady.
FUEL TANK VOLTAGE: 11.0 V AIR COND : ENABLED PURGE FLOW : 2 %

LAMBDA A VOLTS: 0.75 V LAMBDA B VOLTS: 0.39 V INJECTOR OPEN TIME : 4.47 mS

LAMBDA GROUND VOLTS: 0.45 V IGNITION ADVANCE : 3.4 Deg

DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu

T850/3.21

20
 XJR-S 6.0 Litre Engine Management

Road speed
Road speed is expressed in mph. The screen displayed value represents the actual road speed
sensed by the ECM from the road speed sensor via the speed interface unit.

Manifold absolute pressure (manifold depression)

Manifold absolute pressure (MAP) is identified as manifold depression on the display. Do not confuse
this value with manifold vacuum. Manifold absolute pressure is expressed in inches of mercury (in.
hg). When the ignition is switched on (engine stopped) the display should indicate ambient atmo-
spheric pressure (29.92 in. hg at sea level). After starting the engine, the MAP should vary from
approximately 13 in. hg at idle to slightly less than ambient atmospheric pressure at full throttle.

Any faults indicated by this display can be detected by static values as the engine modes vary
(level surface v climbing grade; idle v acceleration) or by fluctuating values as the engine mode
remain steady (idle; cruise on level surface).

Manifold Absolute Pressure (MAP) v Gauge Vacuum (approximate):

MAP Vacuum MAP Vacuum MAP Vacuum
30 in hg 0 23 in hg 7 in hg 16 in hg 14 in hg
29 in hg 1 in hg 22 in hg 8 in hg 15 in hg 15 in hg
28 in hg 2 in hg 21 in hg 9 in hg 14 in hg 16 in hg
27 in hg 3 in hg 20 in hg 10 in hg 13 in hg 17 in hg
26 in hg 4 in hg 19 in hg 11 in hg 12 in hg 18 in hg
25 in hg 5 in hg 18 in hg 12 in hg 11 in hg 19 in hg
44 in hg 6 in hg 17 in hg 13 in hg 10 in hg 20 in hg

Battery voltage
Battery voltage as measured by the ECM is displayed.

Purge valve voltage

In order to open the purge shut off valve, the ECM applies voltage to the valve when the ignition
is switched on. This voltage is less than battery voltage (approximately 9 - 11.5 V). The displayed
value will indicate if the valve is open.

Air injection pump

ENABLED indicates that the air pump flow is being directed to the exhaust ports. DISABLED in-
dicates that the air pump flow is being diverted to the right air cleaner.

Fuel tank level (voltage)

The fuel tank level is expressed as a voltage measured directly from the fuel tank level sender
and ranges from 2 to 10 volts (full to empty). Diagnostic trouble codes related to engine fueling
are disabled when the fuel level is below 6.5 gallons.

Air conditioning compressor

ENABLED indicates that the compressor clutch override circuit is not activated thus allowing com-
pressor operation. DISABLED indicates that the override circuit is activated thus preventing
compressor operation.

Purge flow
The % value indicates if the purge valves are open allowing canister purging. 0% indicates that the
valves are closed. The value at idle (engine at normal operating temperature) will be approximately
2%. Above idle, the % value will vary above 2% depending on engine operating conditions.

21
XJR-S 6.0 Litre Engine Management

Dynamic Display of System Parameters

(continued)
IGNITION ON; ENGINE STOPPED / COLD (AMBIENT)
Oxygen sensor (Lambda) ground voltage
COOLANT TEMPERATURE : 68 Deg. F AIR TEMPERATURE-BANK A : 73 Deg. F The voltage of the ground sensing circuit
FUEL TEMPERATURE : 71 Deg. F AIR TEMPERATURE-BANK B : 72 Deg. F between the ECM, the A bank intake manifold
stud and the engine ground is displayed. With
ENGINE SPEED : STOPPED THROTTLE POSITION : 303 mV the ignition switched on (engine stopped) the
ground signal voltage should read 0.4 - 0.55 V.
ROAD SPEED : 0 MPH MANIFOLD DEPRESSION : 30.3 InHg

BATTERY VOLTAGE : 12.1 V PURGE VALVE VOLTAGE: 9.3 V AIR PUMP: DISABLED
Injector open time (pulse duration)
Injector pulse duration is expressed in millisec-
FUEL TANK VOLTAGE: 9.5 V AIR COND : ENABLED PURGE FLOW : 0 %
onds. The screen displayed value represents
the actual pulse duration output from the ECM
LAMBDA A VOLTS: 4.71 V LAMBDA B VOLTS: 4.80 V INJECTOR OPEN TIME : 65.54mS
for the prevailing engine operating condition.
LAMBDA GROUND VOLTS: 0.47 V IGNITION ADVANCE : 0.0 Deg The pulse duration should increase and de-
crease as engine speed and load (MAP) varies.
DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu
Ignition advance
T850/3.19 The actual ignition timing as referenced from
ENGINE AFTER-START WARM UP the synchronization sensor is displayed.

COOLANT TEMPERATURE : 75 Deg. F AIR TEMPERATURE-BANK A : 72 Deg. F NOTE: It is possible for this timing to be incor-
FUEL TEMPERATURE : 71 Deg. F AIR TEMPERATURE-BANK B : 70 Deg. F rect if the distributor is not referenced to the
crankshaft.
ENGINE SPEED : 880 RPM THROTTLE POSITION : 303 mV

ROAD SPEED : 0 MPH MANIFOLD DEPRESSION : 17.8 InHg

BATTERY VOLTAGE : 14.4 V PURGE VALVE VOLTAGE: 11.2 V AIR PUMP: ENABLED

FUEL TANK VOLTAGE: 11.3 V AIR COND : ENABLED PURGE FLOW : 0 %

LAMBDA A VOLTS: 0.33 V LAMBDA B VOLTS: 1.02 V INJECTOR OPEN TIME : 7.90mS

LAMBDA GROUND VOLTS: 0.43 V IGNITION ADVANCE : 0.0 Deg

DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu

T850/3.20

ENGINE AT IDLE / NORMAL TEMPERATURE

COOLANT TEMPERATURE : 193 Deg. F AIR TEMPERATURE-BANK A : 123 Deg. F

FUEL TEMPERATURE : 119 Deg. F AIR TEMPERATURE-BANK B : 143 Deg. F

ENGINE SPEED : 780 RPM THROTTLE POSITION : 323 mV

ROAD SPEED : 0 MPH MANIFOLD DEPRESSION : 13.1 InHg

BATTERY VOLTAGE : 13.9 V PURGE VALVE VOLTAGE: 11.1 V AIR PUMP: DISABLED

FUEL TANK VOLTAGE: 11.0 V AIR COND : ENABLED PURGE FLOW : 2 %

LAMBDA A VOLTS: 0.75 V LAMBDA B VOLTS: 0.39 V INJECTOR OPEN TIME : 4.47 mS

LAMBDA GROUND VOLTS: 0.45 V IGNITION ADVANCE : 3.4 Deg

DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu

T850/3.21

22
 XJR-S 6.0 Litre Engine Management

SYNCHRONIZATION WARNINGS
Synchronization sensor
There is no value display for the synchroniza- LAMBDA GROUND VOLTS: 0.45 V IGNITION ADVANCE : 3.4 Deg
tion sensor output. Two possible warnings
may be displayed at the bottom of the screen: WARNING! No synch. pulses

DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu

The No synch. pulses warning indicates that
the ECM is not receiving the synchronization
pulse to identify cylinder A 1 at T.D.C. The
Synch. pulse every speed pulse warning indi- LAMBDA GROUND VOLTS: 0.45 V IGNITION ADVANCE : 3.4 Deg
cates that the ECM is receiving 12
synchronization pulses each engine cycle WARNING! Synch. pulse every speed pulse
instead of just one. Either warning identifies a
DYNAMIC DISPLAY OF SYSTEM PARAMETERS Press <Q> to return to main menu
fault in the synchronization sensor or engine
speed sensor and/or circuits. T850/3.22

Oxygen Sensor Feedback Data / Throttle CLOSED LOOP CONTROL DATA

Position (Closed Loop Control Data)
BANK A
% of Lower Clamp
By selecting this option from the main menu,
the operation of the closed loop fuel metering -100 -80 -60 -40 -20 0 20 40 60 80 100
control will be displayed. Values will be dis- BANK A fueling : 100% BANK A idle trim : 10.0%
played only when the engine is running in
BANK B
closed loop control mode (the oxygen sensors % of Lower Clamp
are controlling fuel metering).
-100 -80 -60 -40 -20 0 20 40 60 80 100
The display includes two bar graphs indicating BANK B fueling : 100% BANK B idle trim : -4.2%
the idle fuel metering trim for each bank and a THROTTLE:- 303 mV
bar graph indicating throttle opening as a per-
cent (0 = closed; 100 = wide open). After
starting the engine and bringing it to normal 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
operating temperature, the ECM outputs will
Feedback Data. <Q> or <Esc>-Qu it
control the idle fuel metering trim. As the
ECM attempts to maintain the optimum air/ T850/3.23

fuel ratio, the bars on the graphs should

“hunt” to either side of the zero position. The
graph scales represent how close to the opti-
mum idle fuel metering strategy the system is
operating. The center of the scales (100%) is
optimum. Idle trim is adjustable.

NOTE: A slight deviation between A and B

bank fueling is acceptable.

23
XJR-S 6.0 Litre Engine Management

Engine Set Up

The Zytek Engine Management Service Aid

provides an Engine Set Up option in a step-by-
step procedure. Many of the displays for the
procedures can be used for system operating
analysis as an aid to fault diagnosis. It is not
necessary to run the procedures in sequence
as each item can be accessed independently
as long as the engine is running.

IMPORTANT: Under normal circum-

stances, the engine set up procedures
should only be carried out after component
replacement or engine disassembly and
reassembly.
THROTTLE POSITION SENSOR
Throttle position sensor
Two bar graphs are displayed for the throttle
position sensor check. The upper graph indi-
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 cates throttle opening as a percent (0 =
% THROTTLE closed; 100 = wide open). The lower graph
displays the output voltage from the throttle
position sensor as measured by the ECM.
With the throttle closed (idle), the voltage
118 236 295 355 473
Out of range Acceptable Out of range
should be within the acceptable range: 236-
Throttle Voltage:- 295 mV 355 mV. If adjustment is necessary, attempt
to center the bar at 295 mV. Adjust only if the
voltage is outside the acceptable range.
Set the throttle potentiometer so that the bar is as close as possible to the
centre of the acceptance band shown in the expanded display immediately above.

2) Set up Engine <Q> or <Esc> quits, <SPACE> cycles to next page.

T850/3.24

Throttle linkage adjustment

Three screens cover a verbal description of a
complete throttle linkage adjustment. This
procedure should not be necessary during nor-
mal service or fault diagnosis.

24
 XJR-S 6.0 Litre Engine Management

IGNITION ADVANCE
Ignition advance
After starting the engine and ensuring that the
If the following conditions have been met, the ignition will be fixed to a
displayed conditions are met, the actual igni- constant advance angle of 10 Deg. Exiting this page will cause the ignition
tion timing advance as referenced from the to revert to the normal settings. Parameters shown in highlights are those
which are out of limits. The advance will not be fixed until these parameters
synchronization sensor will be fixed at 10 Deg. are brought within the limits stated.
It is possible for this timing to be incorrect if
the distributor is not correctly referenced to ENSURE THAT;

the crankshaft. The reference to the crank- Water temperature is greater than 165 F Current value is: 188 F
shaft can be checked by using a timing strobe Engine speed is between 100 and 1000 RPM Current value is: 831 RPM
Throttle is set between 276 and 335mV Current value is: 308mV
light to check the engine timing marks on the Road speed is zero Current value is: 0 MPH
front pulley. If necessary, adjust the distribu- No faults are present System is currently: OK
tor to 10 Deg. B.T.D.C. when observed at the
Ignition fixed at 10 Deg.
crankshaft pulley. Exiting this screen will
cause the ignition timing to revert to control by Adjust distributor if required to give 10 Deg when measured
at the crank pulley.
the ECM strategy.
7) Set up engine. <Q> or <Esc> quits, <SPACE> cycles to next page

T850/3.25

Idle speed
Idle speed is adjusted at the extra air valve idle
bleed screw. If necessary, adjust the speed to
750 rpm.

ECM idle fuel trim IDLE FUEL TRIM

The closed loop control system automatically
adjusts the idle fuel metering, however; to cor- <T> - show trim relevant parameters, <S> - save trim in ECU
rectly position the idle fueling on the ECM decrease trim ( ) increase trim

strategy, the ECM idle fuel trim can be ad-

justed. Before adjustment, stop the engine and % of Lower Clamp % of Upper Clamp
disconnect the purge line at the B bank intake
manifold. Block off the intake manifold port.
-100 -80 -60 -40 -20 0 20 40 60 80 100
fueling : 100% idle trim : 3.1%
The displayed bar graph is for B bank; therefore,
keep in mind that the adjustment will affect
both banks as observed in the Oxygen Sensor
Feedback Data / Throttle Position option. Start Set the idle fuel trim potentiometer to cause the feedback bar shown above
to oscillate equally about the zero position
the engine and allow to idle for at least one
minute. Use the left and right arrow keys on
the computer to adjust the trim so that the bar 10) Set up Engine <Q> or <Esc> quits, <SPACE> cycles to next page.
“hunts” to either side of the zero position. Be-
fore exiting this screen, press <S> to save the T850/3.26

trim adjustment.

25
SERVICE TRAINING COURSE 801S JAGUAR EMS: AJ16 OBD II; AJ6 OBD I; V12 OBD I/II

Student Proficiency Test

ANSWER SHEET
Instructions
1. Complete all of the information in the Student Information section of this sheet.
2. Read the questions and possible answers provided on the blue colored test sheets and record your
answers on this sheet. Answer the questions based only on the information provided in the 801S
EMS Self Study book.
3. When complete, fax or mail only the answer sheet to:
Jaguar Cars Service Training Department
ATTN: Service Training Administrator
555 MacArthur Boulevard
Mahwah, New Jersey 07430
FAX: (201) 818-9074
Student Information
Name __________________________________________________ Date of birth _________________
Social Security # – –
Dealer Name _______________________________________________ Dealer # _________________
Address_______________________________________________________________________________

801S Test Answers

Mark an X in the box adjacent to your answer for each question.

1. A B C D 16. A B C D
2. A B C D 17. A B C D
3. A B C D 18. A B C D
4. A B C D 19. A B C D
5. A B C D 20. A B C D
6. A B C D 21. A B C D
7. A B C D 22. A B C D
8. A B C D 23. A B C D
9. A B C D 24. A B C D
10. A B C D 25. A B C D
11. A B C D 26. A B C D
12. A B C D 27. A B C D
13. A B C D 28. A B C D
14. A B C D 29. A B C D
15. A B C D 30. A B C D