Isuzu 1999 RODEO Workshop Manual page 1424

f Evaporative emissions (EVAP) canister purge – Check
for fuel saturation. If full of fuel, check the canister
control and hoses. Refer to Evaporative Emission
(EVAP) Control System .
f 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 the rich condition is corrected. If so,
replace the MAF sensor.
f Check for a leak in 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.
f TP sensor – An intermittent TP sensor output will
cause the system to go rich, due to a false indication
of the engine accelerating.
f 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.
indicated by a powdery white deposit on the portion of
the HO2S exposed to the exhaust stream.
contamination is noticed, replace the affected HO2S.
DTC P0138 – HO2S Circuit High Voltage Bank 1 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 1 HO2S 2 voltage.
Does the Bank 1 HO2S voltage remain above the
specified value?
3 1. Ignition "ON," review and record Tech 2 Failure
Records data.
2. Operate the vehicle within Failure Records
conditions as noted.
3. Using a Tech 2, monitor "DTC" info for DTC P0138
until the DTC P0138 test runs.
4. Note the test result.
Does the Tech 2 indicate DTC P0138 failed this
ignition?
4 1. Ignition "OFF."
2. Disconnect Bank 1 HO2S 1.
3. Ignition "ON."
4. At the HO2S Bank 1 Sensor 2 connector (PCM
side), use a DVM to measure voltages at the high
and low signal terminals.
Are the voltages above the specified range?
RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS
an engine airflow
Silicon
This condition is
If
Action
f Open HO2S Signal Circuit of Faulty HO2S – A poor
connection or open in the HO2S signal circuit can
cause the DTC to set during deceleration fuel mode.
An HO2S which is faulty and not allowing a full voltage
swing between the rich and lean thresholds can also
cause this condition.
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 circuit wiring
and associated terminal connections.
f If none of the 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 P0138 being set during deceleration fuel mode
operation may indicate a condition described in the
"Diagnostic Aids" above. If the DTC P0138 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 cutoff
Go to Step 4
mode)
Go to Step 4
—
3-4 V Go to Step 5
6E2–181
Operate the vehicle while
Yes No
Go to OBD
System
Check
Go to Step 3
Refer to
Diagnostic
Aids
Go to Step 6