Isuzu 2000 Trooper Workshop Manual page 1086

Diagnostic Aids
Check for the following conditions:
D Fuel pressure – An excessively rich fuel mixture can
cause a DTC P0158 to be set. Refer to Fuel System
Diagnosis .
D Rich injector(s) – Perform "Injector Balance Test."
D Leaking injector – Refer to Fuel System Diagnosis .
D Evaporative emissions (EVAP) canister purge – Check
for fuel saturation. If full of fuel, check canister control
and hoses. Refer to Evaporative Emission (EVAP)
Control System .
D MAF sensor –The system can go rich if the MAF
sensor signal indicates
measurement that is not correct. Disconnect the MAF
sensor to see if a rich condition is corrected. If so,
replace the MAF sensor.
D Check for a leaking fuel pressure regulator diaphragm
by checking the vacuum line to the regulator for the
presence of fuel. There should be no fuel in the
vacuum line.
D TP sensor – An intermittent TP sensor output will
cause the system to go rich, due to a false indication
of the engine accelerating.
D Shorted Heated Oxygen Sensor (HO2S) – If the HO2S
is internally shorted, the HO2S voltage displayed on
the Tech 2 will be over 1 volt. Try disconnecting the
affected HO2S with the key "ON," engine "OFF." If the
displayed HO2S voltage changes from over 1000 mV
to around 450 mV, replace the HO2S.
contamination of the HO2S can also cause a high
HO2S voltage to be indicated.
DTC P0158 – HO2S Circuit High 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 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 above the
specified value?
3 1. Ignition "ON."
2. Review and record Tech 2 Failure Records data.
3. Operate the vehicle within Failure Records
conditions as noted.
4. Using a Tech 2, monitor "DTC" info for DTC P0158
until the DTC P0158 test runs.
5. Note the test result.
Does the Tech 2 indicate DTC P0158 failed this
ignition?
TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
an engine airflow
Silicon
This condition is
Action
indicated by a powdery deposit on the portion of the
HO2S exposed to
contamination is noticed, replace the affected HO2S.
D Open HO2S signal or low circuit, or faulty HO2S – A
poor connection or open in the HO2S signal or low
circuit can cause the DTC to set during deceleration
fuel cutoff mode operation. An HO2S which is faulty
and does not allow full voltage swing between the rich
and lean thresholds can also cause this condition.
Operate the vehicle while monitoring the HO2S voltage
with a Tech 2. If the HO2S voltage is limited within a
range between 300 mV to 600 mV, check the HO2S
signal and low circuit wiring and associated terminal
connections. If the wiring and connections are OK,
replace the HO2S.
D If none of above conditions are present, replace the
affected HO2S.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. DTC P0158 being set during deceleration fuel cutoff
mode operation may indicate a condition described
in the "Diagnostic Aids" above. If the DTC P0158
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
—
952 mV
(500 mV in
deceleration
fuel cut-out
Go to Step 4
mode)
Go to Step 4
—
6E–217
the exhaust stream.
Yes No
Go to OBD
System
Check
Go to Step 3
Refer to
Diagnostic
Aids
If