2004 ISUZU TF SERIES Workshop Manual

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Page 2185 of 4264

ISUZU TF SERIES 2004 Workshop Manual 3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-189
Diagnostic Trouble Code (DTC) P0123 (Flash Code 21) Throttle Position
Sensor Circuit High Input
Step Action Value (s) Yes No
1
Was the "On-Board

Page 2186 of 4264

ISUZU TF SERIES 2004 Workshop Manual 6E-190 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Step Action Value (s) Yes No
6
Using the DVM and check the TPS.
1. Ignition "Off", engine "Off".
2. Disconnect TPS connector.
3. Measure

Page 2187 of 4264

ISUZU TF SERIES 2004 Workshop Manual 3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-191
Step Action Value (s) Yes No
9
Using the DVM and check the TPS signal circuit.
1. Ignition "On", engine "Off".
2. Disconnect the TPS connect

Page 2188 of 4264

ISUZU TF SERIES 2004 Workshop Manual 6E-192 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Step Action Value (s) Yes No
Breaker box is not available:
1. Ignition "Off", engine "Off".
2. Disconnect the TPS connector and ECM connecto

Page 2189 of 4264

ISUZU TF SERIES 2004 Workshop Manual 3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-193
DIAGNOSTIC TROUBLE CODE (DTC) P0131 (FLASH CODE 15) O2 SENSOR
CIRCUIT LOW VOLTAGE (BANK 1 SENSOR 1)
DIAGNOSTIC TROUBLE CODE (DTC) P0151 (FLASH CODE 15)

Page 2190 of 4264

ISUZU TF SERIES 2004 Workshop Manual 6E-194 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Condition For Setting The DTC and Action Taken When The DTC Sets
Flash
Code Code Type DTC Name DTC Setting Condition Fail-Safe (Back Up)
P0131 A

6E-194 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Condition For Setting The DTC and Action Taken When The DTC Sets
Flash
Code Code Type DTC Name DTC Setting Condition Fail-Safe (Back Up)
P0131 A O2 Sensor Circuit Low
Voltage (Bank 1
Sensor 1) 15
P0151 A O2 Sensor Circuit Low
Voltage (Bank 2
Sensor 1) 1. No DTC relating to ECT sensor, CMP sensor, CKP sensor,
VSS, injector control circuit, ignition control circuit and O2
sensor circuit no activity (bank 1 & 2).
2. Engine speed is between 1000rpm and 4000rpm.
3. Engine coolant temperature is between 70C and 110C.
4. Vehicle speed is between 0km/h and 120km/h.
5. Engine load is between 80% and 160%.
6. Throttle position fluctuation is below 0.28V.
7. O2 sensor bank 1 or bank 2 output voltage is more than
400mV for 50 seconds. "Open Loop" fuel control.

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) supplies a bias
voltage of about 450 mV between the heated oxygen
sensor (HO2S) signal high and signal low circuits. The
ECM constantly monitors the HO2S signal during
“closed loop" operation and compensates for a rich o
r
lean condition by decreasing or increasing injector pulse
width as necessary. If HO2S voltage remains
excessively low for an extended period of time, DTC
P0131 or P0151 will be set.
DIAGNOSTIC AIDS
Check for the following conditions:
Heated oxygen sensor wiring – The sensor pigtail
may be routed incorrectly and contacting the exhaus
t
system.
Poor ECM to engine block grounds.
Fuel pressure – The system will go lean if pressure is
too low. The ECM can compensate for some
decrease. However, If fuel pressure is too low, a DTC
P0131 or P0151 may be set. Refer to 6E-116 Fue
l
System Diagnosis.

Lean injector(s) – Perform “Injector Balance Test."
Exhaust leaks – An exhaust leak may cause outside
air to be pulled into the exhaust gas stream past the
HO2S, causing the system to appear lean. Check fo
r
exhaust leaks that may cause a false lean condition
to be indicated.
MAF sensor –The system can go lean if the MAF
sensor signal indicates an engine airflo
w
measurement that is not correct. Disconnect the MAF
sensor to see if the lean condition is corrected. If so,
replace the MAF sensor.
Fuel contamination –Water, even in small amounts,
can be delivered to the fuel injectors. The water can
cause a lean exhaust to be indicated. Excessive
alcohol in the fuel can also cause this condition.
Refer to 6E-116 Fuel System Diagnosisfor the
procedure to check for fuel contamination.
If none of the above conditions are present, replace
the affected HO2S.

Page 2191 of 4264

ISUZU TF SERIES 2004 Workshop Manual 3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-195
Diagnostic Trouble Code (DTC) P0131 (Flash Code 15) O2 Sensor Circuit Low
Voltage (Bank 1 Sensor 1)
Diagnostic Trouble Code (DTC) P0151 (Flash Code 15)

Page 2192 of 4264

ISUZU TF SERIES 2004 Workshop Manual 6E-196 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Step Action Value (s) Yes No
5
Using the DVM and check the O2 sensor circuit for the
affected bank.
1. Ignition "On", engine "Off".
2. Discon

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