Isuzu 2000 Trooper Workshop Manual page 1083

6E–214
TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Aids
Check for the following conditions:
D Heated oxygen sensor wiring – The sensor pigtail may
be mispositioned and contacting the exhaust system.
D Poor PCM to engine grounds.
D Fuel pressure – A condition which causes a lean
exhaust can cause DTC P0157 to set. The system will
go lean if pressure is too low.
compensate for some decrease.
pressure is too low, a DTC P0157 may be set. Refer
to Fuel System Diagnosis .
D Lean injector(s) – Perform "Injector Balance Test."
D Vacuum leaks – Check for disconnected or damaged
vacuum hoses and for vacuum leaks at the intake
manifold, throttle body, EGR system, and PCV system.
D Exhaust leaks – An exhaust leak may cause outside air
to be pulled into the exhaust gas stream past the
HO2S, causing the DTC P0157 to set. Check for
exhaust leaks near the Bank 1 HO2S 2 sensor.
D MAF sensor – The system can go lean if the MAF
sensor signal indicates
DTC P0157 – HO2S Circuit Low Voltage Bank 2 Sensor 2
Step
1 Was the "On-Board Diagnostic (OBD) System Check"
performed?
2 1. Install the Tech 2.
2. Run the engine at operating temperature.
3. Operate the vehicle within the parameters specified
under "Conditions for Setting the DTC" criteria
included in Diagnostic Support.
4. Using a Tech 2, monitor Bank 2 HO2S 2 voltage.
Does the Bank 2 HO2S 2 voltage remain below the
specified value?
3 1. Ignition "ON," engine "OFF."
2. Review and record Tech 2 Failure Records data and
note parameters.
3. Operate the vehicle within Failure Records
conditions as noted.
4. Using a Tech 2, monitor "DTC" info for DTC P0157
until the DTC P0157 test runs.
5. Note the test result.
Does the Tech 2 indicate DTC P0157 failed this
ignition?
4 1. Turn the ignition "OFF."
2. Disconnect the PCM.
3. Check the Bank 2 HO2S 2 high and low signal
circuits for a short to ground or a short to the heater
ground circuit.
Were Bank 2 HO2S 2 signal circuits shorted?
5 Repair the Bank 1 HO2S 2 signal circuit.
Is the action complete?
The PCM can
However, if fuel
an engine airflow
Action
measurement that is not correct. Disconnect the MAF
sensor to see if the condition is corrected. If so, replace
the MAF sensor.
D Fuel contamination – Water, even in small amounts,
can be delivered to the fuel injectors. The water can
cause a lean exhaust to be indicated.
alcohol in the fuel can also cause this condition. Refer
to Fuel System Diagnosis for the procedure to check
for fuel contamination.
D If none of above conditions are present, replace the
affected HO2S 2.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. DTC P0157 failing during operation may indicate a
condition described in the "Diagnostic Aids" above.
If the DTC P0157 test passes while the Failure
Records conditions are being duplicated, an
intermittent condition is indicated.
Value(s)
— Go to Step 2
22 mV Go to Step 4
— Go to Step 4
— Go to Step 5
— Verify repair
Excessive
Yes No
Go to OBD
System
Check
Go to Step 3
Refer to
Diagnostic
Aids
Go to Step 6
—