Isuzu 2000 Trooper Workshop Manual page 1039

6E–170
TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
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 system to appear lean. Check for
exhaust leaks that may cause a false lean condition to
be indicated.
D MAF sensor – The system can go lean if the MAF
sensor signal indicates
measurement that is not correct. Disconnect the MAF
sensor to see if the lean 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.
DTC P0131 –HO2S Circuit Low Voltage Bank 1 Sensor 1
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 1 HO2S 1 voltage.
Does the Bank 1 HO2S 1 voltage remain below the
specified value?
3 1. Ignition "ON," engine "OFF," review and record Tech
2 Failure Records data and note parameters.
2. Operate the vehicle within Failure Records
conditions as noted.
3. Using a Tech 2, monitor "DTC" info for DTC P0131
until the DTC P0131 test runs.
Note test result.
Does Tech 2 indicate DTC P0131 failed this ignition?
4 1. Turn the ignition "OFF."
2. Disconnect the PCM.
3. Check the Bank 1 HO2S 1 high and low circuits for a
short to ground or a short to the heater ground
circuit.
Are the Bank 1 HO2S 1 signal circuits shorted to
ground?
5 Repair the Bank 1 HO2S 1 signal circuit.
Is the action complete?
6 1. Turn the ignition "OFF," HO2S 1 and PCM
disconnected.
2. Check for continuity between the high and low
signal circuits.
Was there continuity between the high and low circuits?
an engine airfiow
Excessive
Action
D If none of the above conditions are present, replace the
affected HO2S.
Test Description
Number(s) below refer to step numbers on the diagnostic
chart.
3. DTC P0131 failing during operation may indicate a
condition described in the "Diagnostic Aids" above.
If the DTC P0131 test passes while the Failure
Records conditions are being duplicated, an
intermittent condition is indicated.
Reviewing the Failure Records vehicle mileage since the
diagnostic test last failed may help determine how often
the condition that caused the DTC to be set occurs. This
may assist in diagnosing the condition.
Value(s)
— Go to Step 2
22 mV Go to Step 4
Go to Step 4
—
— Go to Step 5
— Verify repair
— Go to Step 7
Yes No
Go to OBD
System
Check
Go to Step 3
Refer to
Diagnostic
Aids
Go to Step 6
—
Go to Step 8