05174
DIAGNOSTICS
DTC
P0420
SFI SYSTEM
05DJU01
CATALYST SYSTEM EFFICIENCY BELOW
THRESHOLD (BANK 1)
CIRCUIT DESCRIPTION
The ECM compares the 2 waveforms of the heated oxygen sensors located before and after the catalyst
to determine whether or not the catalyst performance has deteriorated.
Airfuel ratio feedback compensation keeps the waveform of the heated oxygen sensor in front of the catalyst alternates between back and forth, from RICH to LEAN.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor behind the catalyst switches
back and forth between RICH and LEAN much more slowly than the waveform of the heated oxygen sensor
in front of the catalyst.
When both waveforms change at a similar rate, it indicates that the catalyst performance has deteriorated.
DTC No.
P0420
DTC Detecting Condition
Trouble Area
After engine and catalyst are warmed up, and while vehicle is
driven within set vehicle and engine speed range, waveforms
of heated oxygen sensors have same amplitude (2 trip detection logic)
Gas leakage in exhaust system
Heated oxygen sensor
Threeway catalytic converter
MONITOR DESCRIPTION
The vehicle is equipped with the two heated oxygen sensors (O2S). One is mounted upstream from the
threeway catalytic (TWC) converters (front heated oxygen sensor sensor 1), the second is mounted
downstream (rear heated oxygen sensor sensor 2). The catalyst efficiency monitor compares the sensor
1 and 2 signals in order to calculate TWC ability to store oxygen.
During normal operation, the TWC stores and releases oxygen as needed. This results in low oxygen variations in the post TWC exhaust stream as shown.
Waveform of Heated
Oxygen Sensor
(before Catalyst)
Waveform of Heated
Oxygen Sensor
(before Catalyst)
Waveform of Heated
Oxygen Sensor
(after Catalyst)
Normal Catalyst
Deteriorated Catalyst
Waveform of Heated
Oxygen Sensor
(after Catalyst)
A83860
2004 SCION xB REPAIR MANUAL (RM1031U)
Author:
Date:
334
05175
DIAGNOSTICS
SFI SYSTEM
Heated Oxygen Sensor Signal Length
Signal Length
Sensor
Output
Voltage
Time
A82718
MONITOR STRATEGY
Related DTCs
P0420
Bank 1 catalyst is deterioration
Main sensors
Required sensors/components
Frequency of operation
Duration
MIL operation
Sequence of operation
Front and rear heated oxygen sensor
Mass air flow sensor, engine coolant temperature
sensor, engine speed sensor, intake air temperature sensor
Related sensors
Once per driving cycles
90 sec
2 driving cycles
None
TYPICAL ENABLING CONDITIONS
Specification
Item
The monitor will run whenever the following DTCs are not present
Battery voltage
Intake air temperature
Minimum
Maximum
See List of Disable a Monitor table (On page 0524)
11 V
10C (14F)
Idle
OFF
Intake air amount
Engine speed
Engine coolant temperature
8 g/sec
25 g/sec
4,500 rpm
75C (167F)
Estimated catalyst temperature conditions
are met:
1 and 2
1. Estimated temperature of upstream catalyst
470C (878F)
800C (1,472F)
2. Estimated temperature of downstream
catalyst
470C (878F)
800C (1,472F)
Fuel system status
Closed loop
Accumulated time with above parameters
are met
30 sec 2 times
TYPICAL MALFUNCTION THRESHOLDS
Detection Criteria
Threshold
Catalyst deterioration level (heated oxygen sensor locus
length ratio)
0.3 or more
Number of times detection
2 times
2004 SCION xB REPAIR MANUAL (RM1031U)
Author:
Date:
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DIAGNOSTICS
SFI SYSTEM
COMPONENT OPERATING RANGE
Parameter
Standard Value
Catalyst deterioration level (heated oxygen sensor locus
length ratio)
0 to 1
MONITOR RESULT (MODE 06 DATA)
Test ID
Comp ID
Description of test data
Description of test limit
Unit
Conversion factor
$01
$01
Catalyst deterioration (bank 1) level determined by waveforms of the
heated oxygen sensor.
Malfunction criteria for catalyst deterioration
Multiply by
0.007812
(no dimension)
Refer to page 0526 for detailed information on CHECKING MONITOR STATUS.
CONFIRMATION DRIVING PATTERN
Engine Speed
2,500 to 3,000 rpm
(c)
(d)
3 minutes
Check
(b)
Idling
Ignition OFF
(a)
Warmed up
Time
A58693
(a)
(b)
(c)
(d)
OX Signal Waveform (Oscilloscope)
1.0 V
Connect the handheld tester to the DLC3, or connect the
probe of the oscilloscope between terminals HTL, HTL2,
OXL1, OXL2 and E1 of the ECM connector.
Start the engine and warm it up with all the accessories
switched OFF until the engine coolant temperature becomes stable.
Run the engine at 2,500 to 3,000 rpm for about 3 minutes.
After confirming that the waveform of the bank 1 sensor
1 (OXL1) which oscillates between 0 V and 1 V under a
feedback to the ECM, check the waveform of the bank 1
sensor 2 (OXL2).
HINT:
If there is malfunction in the system, the waveform of sensor
2 (OXL2) may become a similar to the one of sensor1 (OXL1)
shown in the diagram on the left.
0V
200 msec. /Division
A58694
2004 SCION xB REPAIR MANUAL (RM1031U)
Author:
Date:
336
05177
DIAGNOSTICS
SFI SYSTEM
INSPECTION PROCEDURE
HINT:
Read freeze frame data using the handheld tester or the OBD II scan tool. Freeze frame data records the
engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether
the vehicle was running or stopped, the engine was warmed up or not, the airfuel ratio was lean or rich,
etc. at the time of the malfunction.
1
(a)
(b)
(c)
(d)
CHECK OTHER DTCS OUTPUT(IN ADDITION TO DTC P0420)
Connect the handheld tester or the OBD II scan tool to the DLC3.
Turn the ignition switch ON and push the handheld tester or the OBD II scan tool main switch ON.
Select the item DIAGNOSIS / OBD/MOBD / DTC INFO / CURRENT CODES.
Read the DTCs using the handheld tester or the OBD II scan tool.
Result:
Display (DTC output)
Proceed to
Only P0420 is output
P0420 and other DTCs are output
HINT:
If any other codes besides P0420 are output, perform the troubleshooting for those DTCs first.
B
GO TO RELEVANT DTC CHART
(See page 0534)
CHECK FOR EXHAUST GAS LEAKAGE
NG
REPAIR OR REPLACE EXHAUST
LEAKAGE POINT (See page 153)
GAS
OK
INSPECT HEATED OXYGEN SENSOR(BANK 1 SENSOR 1) (See page 0596)
Refer to the hint below.
NG
REPLACE HEATED OXYGEN SENSOR
OK
INSPECT HEATED OXYGEN SENSOR(BANK 1 SENSOR 2) (See page 05122)
Refer to the hint below.
NG
REPLACE HEATED OXYGEN SENSOR
OK
REPLACE THREEWAY CATALYTIC CONVERTER (EXHAUST MANIFOLD)
2004 SCION xB REPAIR MANUAL (RM1031U)
Author:
Date:
337
05178
DIAGNOSTICS
SFI SYSTEM
HINT:
Handheld tester only:
The following procedure enables the technician to identify a trouble area if malfunction in both front and rear
heated oxygen sensors other than the catalyst converter, or the malfunction that indicates the actual airfuel
ratio extremely RICH or LEAN.
(a) Perform ACTIVE TEST using the handheld tester (A/F CONTROL).
HINT:
A/F CONTROL is ACTIVE TEST which changes the injection volume 12.5 % or +25 %.
(1) Connect the handheld tester to the DLC3 on the vehicle.
(2) Turn the ignition switch ON.
(3) Warm up the engine by running the engine at 2,500 rpm for approximately 3 minutes.
(4) Select the item DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/ A/F CONTROL.
(5) Perform A/F CONTROL with the engine in an idle condition (press the right or left button).
Result:
Heated oxygen sensor reacts in accordance with increase and decrease of injection volume:
+25 % rich output: More than 0.55 V
12.5 % lean output: Less than 0.4 V
NOTICE:
There is a delay of few seconds in the sensor 1 (front sensor) output, and there is about 20 seconds
delay at maximum in the sensor 2 (rear sensor).
Output voltage of heated oxygen
sensor (sensor 1: front sensor)
Injection volume
+25 %
12.5 %
12.5 %
Case 1 Output voltage
Less than 0.4V
Output voltage
OK
Injection volume
More than 0.55 V
OK
Less than 0.4V
Injection volume
+25 %
+25 %
12.5 %
12.5 %
Case 2 Output voltage
No reaction
Sensor 1: front sensor
(sensor 1, heater, sensor 1
circuit)
Output voltage
NG
Injection volume
More than 0.55 V
OK
Less than 0.4V
Injection volume
+25 %
+25 %
12.5 %
12.5 %
Case 3 Output voltage
Sensor 2: rear sensor
(sensor 2, heater, sensor 2
circuit)
Output voltage
More than 0.55 V
Less than 0.4V
OK
Injection volume
NG
No reaction
Injection volume
+25 %
+25 %
12.5 %
12.5 %
Case 4 Output voltage
No reaction
Mainly suspect
trouble area
Injection volume
+25 %
More than 0.55 V
Output voltage of heated oxygen
sensor (sensor 2: rear sensor)
Output voltage
NG
No reaction
NG
Extremely rich or lean actual
airfuel ratio
(Injector, fuel pressure, gas
leakage in exhaust system,
etc.)
2004 SCION xB REPAIR MANUAL (RM1031U)
Author:
Date:
338
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DIAGNOSTICS
SFI SYSTEM
The following A/F CONTROL procedure enables the technician to check and graph the voltage outputs of
both the heated oxygen sensors.
For displaying the graph indication, enter ACTIVE TEST / A/F CONTROL / USER DATA, then select O2S
B1S1 and O2S B1S2 by pressing YES button and push ENTER button before pressing F4 button.
2004 SCION xB REPAIR MANUAL (RM1031U)
Author:
Date:
339
