CHAPTER
13
Body Control
Modules
Instructor Name: (Your Name)
Copyright 2014 Delmar, Cengage Learning
Learning Objectives
Explain the concept of virtual fusing
List the type of inputs and outputs used by a
typical body control module
Discuss the reasons that most electronic
control modules used in modern trucks make
use of a reference ground
Discuss the difference between a
conventional switch and diagnosable switch
Describe how a body control module can act
as a turn signal flasher
Copyright 2014 Delmar, Cengage Learning
Learning Objectives (continued)
Retrieve DTCs stored in memory related to
the body controller
List the main components of the International
Diamond Logic and Freightliner Smart
Plex multiplexed electrical systems
Describe how a Freightliner Smart Switch
operates
Explain the concept of ghost voltage and
describe how it can lead to confusion when
diagnosing an electrical problem
Copyright 2014 Delmar, Cengage Learning
International Multiplexed
Electrical System
Referred to as the Diamond Logic
electrical system
Between 2001-2006 body control modules
were referred to as electrical system
controller (ESC)
In 2007 the name was changed to the
body controller
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International ESC
Figure 13-1 International electrical system
controller (ESC). Copyright 2014 Delmar, Cengage Learning
International Body Controller
Figure 13-2
International
body
controller.
Copyright 2014 Delmar, Cengage Learning
Overview of Body Controller
Figure 13-3 Overview of body
controller. Copyright 2014 Delmar, Cengage Learning
Tech Tip
Think of the J1939 data link as both being
an input and an output device for most
electronic devices. The messages
received by a module are inputs; the
messages sent by a module are the
outputs.
Copyright 2014 Delmar, Cengage Learning
Typical Body Control Module
Horn Circuit
Figure 13-5 Typical body control module
horn circuit.
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Body Controller Outputs
The body controller has three main
types of outputs:
High side drivers
Low side drivers
Messages transmitted on the J1939 data link
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High Side Driver
Capable of sourcing high levels of current
The high side drivers used in body
controllers are power MOSFETs (FETs)
Some FETs are capable of sourcing 20A
continuously
Smart FETs can monitor the amount of
current that the FET is conduction
Copyright 2014 Delmar, Cengage Learning
Current Feedback For Virtual Fusing
Figure 13-6 The high side driver measures the
current being conducted and feeds back this
information to the microprocessor as a proportional
voltage. Copyright 2014 Delmar, Cengage Learning
Low Side Drivers
Current ratings of 1A or less
Commonly used in body controllers
Low side drivers sink a path to ground
Typically used to energize relay coils or
small solenoids
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Body Controller Inputs
There are three main types of inputs
to the body controller:
Hardwired inputs from switches and sensors
Messages received from a proprietary switch
data link
Messages received from the J1939 data link
Copyright 2014 Delmar, Cengage Learning
Hardwired Inputs
Conventional switch to control electrical
devices
Reference ground is a single ground that
all sensors and switches share
Reference ground is connected to chassis
ground but in one location usually inside
the electronic module
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Common Reference Ground Located in
Body Controller
Figure 13-7 The common reference ground point inside of
body controller is connected to chassis ground at only one
location.
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CAUTION
It is vital that any electronic system that uses a
reference ground only be grounded in
accordance with OEM recommendations. Even
though reference ground may appear to be the
same as chassis ground, connecting the
reference ground to chassis ground outside the
electronic module may result in the truck
having intermittent EMI induced problems that
are nearly impossible to duplicate or
troubleshoot.
Copyright 2014 Delmar, Cengage Learning
Open and Closed Switches
with Digital Input
Figure 13-8
Open switch
(upper) and
closed switch
(lower) with
digital input.
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Open Circuit Prevents Digital Input From
Detecting Switch is Closed
Figure 13-9 Open circuit prevents digital input from detecting that
switch is closed; input voltage should be 0V with switch closed, but
is actually +12V.
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Diagnosable Switch With Contacts Open
and Closed
Figure 13-10 Diagnosable switch with contacts
open and closed. Copyright 2014 Delmar, Cengage Learning
Diagnosable Switch Open;
8V at the Input Terminal
Figure 13-11 Diagnosable switch open; 8V at
input terminal.
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Diagnosable Switch Closed; 6V at the
Input Terminal
Figure 13-12 Diagnosable switch closed; 6V at
input terminal.
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Diagnosable Switch Open Circuit; 12V at
the Input Terminal
Figure 13-13 Diagnosable switch open circuit; 12V at
input terminal. Copyright 2014 Delmar, Cengage Learning
Switch Packs
International trucks with body controllers
use switch packs using J1708/J1578
specification data link
This proprietary link is not the same as the
J1708/J1587 data link connected to the
power train or ECM modules
Switch packs are rockers that require
switch actuators installed in them
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Switch Pack with
Switch Actuators Removed
Figure 13-14 Switch pack with the switch
actuators removed. Copyright 2014 Delmar, Cengage Learning
Tech Tip
Think of high side drivers as being like
conventional relays. A small signal
provided by the microprocessor is used to
control a large amount of current.
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Body Controller Headlight Circuit
Figure 13-15 Body controller headlamp circuit.
EGC contains headlamp switch.
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Turn-Signal System, International Truck
With Body Controller
Figure 13-16 Turn-signal system on International trucks with body
controller. Two switches are inputs; four high side drivers are
outputs.
Copyright 2014 Delmar, Cengage Learning
Tech Tip
The body controller only powers the
applicable trailer light relay control circuit.
The body controller does not directly
supply the current to the trailer lighting. A
conventional CPD such as a fuse or a
circuit breaker in the PDC is used to
protect the trailer wiring, not virtual fusing.
Copyright 2014 Delmar, Cengage Learning
A/C System Inputs; Outputs Is A/C
Clutch High Side Driver
Figure 13-17 Air conditioning system inputs; output is A/C
clutch high side driver.
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Cruise Control Related Inputs Output is
J1939 Message to Engine ECM
Figure 13-18 Cruise control related inputs; output is J1939
message to engine ECM.
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Primary and Secondary Air Pressure
Measurement System
Figure 13-19
Primary and
secondary air
pressure
measurement
system.
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Windshield Wiper System Outputs
Figure 13-20 Windshield wiper system outputs; one high side driver and
two low side drivers.
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Wiper Switch Inputs and Truth Table
Figure 13-21
Wiper switch
inputs and
truth table.
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Tech Tip
An open windshield wiper switch connection
on an International truck with a body controller
causes the wiper to operate at high speeds at
any time the key switch is in the ignition
position. Additionally, a short to ground of the
windshield washer pump control circuit will
cause the windshield wipers to operate at low
speed any time the key switch is in the ignition
position because the controller is falsely
detecting that the washer switch is depressed.
Copyright 2014 Delmar, Cengage Learning
Freightliner Multiplexed Electrical System
Freightliner refers to their multiplexed
electrical system as SmartPlex
The bulkhead module (BHM) acts as the
primary command module for body and
chassis electrical systems.
The chassis module (CHM) is the other
standard electronic module
The CHM is a slave or dependent that
receives commands from the BHM
Copyright 2014 Delmar, Cengage Learning
Freightliner SmartPlexTM Electronic
Module Locations
Figure 13-22 Freightliner SmartPlexTM electronic
module locations. Copyright 2014 Delmar, Cengage Learning
Bulkhead Module (BHM)
Main electronic controller for Freightliner
SmartPlexTM electrical system
The BHM is connected to the J1939 data link and
transmits and receives information from other
electronic modules
The BHM is hardwired to several inputs in the
cab
Direct hardwired high side outputs include horn,
dome light, left side low-beam and high beam
headlights
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Freightliner Smart Switch Schematic
Figure 13-25
Freightliner smart
switch schematic.
Copyright 2014 Delmar, Cengage Learning
Chassis Module (CHM)
Contains several high side driver FETs that
source current to several chassis electrical
features
The CHM is dependent on commands from
the BHM via the J1939 data link
High side driver outputs include park and
marker lights, back-up lamps, turn signal
lamps, right side high and low beam
headlights and fog lamps
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Freightliner Multifunction Switch
Figure 13-28
Freightliner
multifunction switch.
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Freightliner Multiplexed
Headlamp Control
Figure 13-29 Freightliner multiplexed
headlamp control.
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Troubleshooting The Multiplexed Truck
Best if performed with OEM diagnostic software
and a PC, referred to as a electronic service
tool (EST)
Software for Freightliner trucks is ServiceLink
Software for International trucks is diamond
Logic
This software permits viewing diagnostic trouble
codes by the body controller and EGC, along
with fault descriptions
Copyright 2014 Delmar, Cengage Learning
International Diagnostic
Code Retrieval
Place the ignition switch in the ignition or
accessory position
Set the park brake
Depress the cruise control ON and
RESUME switches at the same time
The EGC will indicate the number of DTCs
that exist
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Diagnostic Trouble Codes Display
Figure 13-32 Diagnostic trouble codes as displayed
in instrument panel cluster odometer display.
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SAE J1939 Suspect
Parameter Number
Figure 13-33 SAE J1939 suspect parameter number
(SPN).
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SAE J1939 Failure Mode Indicator
Figure 13-34 SAE J1939 failure
mode indicator.
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ORH Condition at a Pulled-Up Input With
Open Circuit
Figure 13-36 ORH condition at a pulled-up input with an
open circuit.
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ORL Condition at a Pulled-Up Input with
Grounded Circuit
Figure 13-37 ORL condition at a pulled-up input with a ground
circuit.
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ORL Condition at a Pulled-Down Input
With Open Circuit
Figure 13-38 ORL condition at a pulled-down input with an
open circuit.
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Summary
The body control module on International
High Performance Vehicles is called the
electrical system controller (ESC) on
model year 2001-2006 trucks and the body
controller on 2007 and later year trucks.
The body controller or ESC contains a
microprocessor. The body controller or
ESC uses information obtained from input
sources to control the outputs.
Copyright 2014 Delmar, Cengage Learning
Summary(continued)
Outputs of the body controller include high side
drivers, low side drivers, and messages on the J1939
data link.
Input sources for the body controller include
messages from the J1939 data link, messages from
the switch link, and hardwired inputs such as switches
and sensors.
A reference ground scheme is commonly used in
automotive electronics to minimize the effects of
electromagnetic interference and to improve
measurement accuracy for sensor circuits.
Copyright 2014 Delmar, Cengage Learning
Summary(continued)
A diagnosable switch is a special switch
that provides specific values of resistance,
unlike a conventional switch, which is
either an open circuit or a near 0. A
diagnosable switch is connected to an
analog input. This permits circuit failures
such as an open circuit or a shorted-to-
ground circuit to be diagnosed.
Copyright 2014 Delmar, Cengage Learning
Summary(continued)
The body controller controls several electrical
system features, including headlamps, turn
signals, stop lamps, and windshield wipers. The
various switches act as inputs to the body
controller through either hardwiring or
multiplexing. The body controller microprocessor
makes decisions based on its programming and
provides an output in the form of energizing a
high side driver, energizing low side driver, or
transmitting a data link message.
Copyright 2014 Delmar, Cengage Learning
Summary(continued)
Self-diagnostics assists in troubleshooting
the body controller. Diagnostic trouble
codes may be logged to indicate a circuit
that is out of range high or out of range low.
The Freightliner SmartPlexTM system uses
two or more separate modules to control
body electrical features. The bulkhead
module (BHM) controls the chassis module
(CHM) via the J1939 data link.
Copyright 2014 Delmar, Cengage Learning
Summary(continued)
The Freightliner SmartPlexTM uses optional smart
switches to control electrical system features.
Each smart switch contains two identification
resistors that uniquely define the switch function.
The instrument cluster in the Freightliner
SmartPlexTM system is called the ICU. The ICU
acts as the input device for the stalk mounted
multifunction switch. The ICU transmits the
status of the multifunction switch inputs on the
J1939 data link.
Copyright 2014 Delmar, Cengage Learning
Summary(continued)
Diagnostic trouble codes (DTCs) are used
to indicate that an electrical module has
detected and abnormal condition. DTCs
may indicate a sensor in-range operating
condition, such as engine coolant
temperature is too high. DTCs may also
indicate sensor out of range conditions,
such as open circuits or shorts to grounds.
A J1939 DTC consists of an SPN and FMI.
Copyright 2014 Delmar, Cengage Learning
Summary(continued)
Ghost voltage describes an open circuit
measurement of a voltage by a DMM in a
circuit with high resistance. Ghost voltage
can result in misdiagnosis.
Copyright 2014 Delmar, Cengage Learning
