Isuzu Trooper 1999 Workshop Manual page 995

6E–194
TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Aids
Check for the following conditions:
f Fuel pressure – An excessively rich fuel mixture can
load the catalyst, causing a DTC P0144 to be set.
Refer to Fuel System Diagnosis .
f Rich injector(s) – Perform "Injector Balance Test."
f Leaking injector– Refer to Fuel System Diagnosis .
f 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 .
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 a rich condition is corrected. If so,
replace the MAF sensor.
f Check for a leaking fuel pressure regulator diaphragm
by checking the vacuum line to regulator for the
presence of fuel. There should be no fuel in the vacuum
sensor.
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
DTC P0144 – HO2S Circuit High Voltage Bank 1 Sensor 3
Step
1 Was the "On-Board Diagnostic (OBD) System Check"
performed?
2 1. Install 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 1 HO2S 3 voltage.
Does the Bank 1 HO2S 3 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 P0144
until the DTC P0144 test runs.
4. Note test result.
Does Tech 2 indicate DTC P0144 failed?
an engine airflow
Silicon
Action
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.
f Open HO2S High or Low Circuit or Faulty HO2S — A
poor connection or open in the HO2S high or low 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. 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 high and low
circuit wiring and associated terminal connections.
f 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 P0144 being set during deceleration fuel cutoff
mode operation may indicate a condition described
in the "Diagnostic Aids" above. If the DTC P0144
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
This condition is
Yes No
Go to OBD
System
Check
Go to Step 3
Refer to
Diagnostic
Aids
If