1998 ISUZU TROOPER check engine

6E±151 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0152 HO2S Circuit HIGH Voltage Bank 2
Sensor 1
060RW190
Circuit Description
The powertrain control module (PCM) supplies a bias
voltage of about 450 mV between the heated oxygen
sensor (HO2S) signal high and signal low circuits. When
measured with a 10 megaohm digital voltmeter, this may
display as low as 320 mV. The oxygen sensor varies the
voltage within a range of about 1000 mV when the
exhaust is rich, down through about 10 mV when exhaust
is lean. The PCM constantly monitors the HO2S signal
during ªclosed loopº operation and compensates for a rich
or lean condition by decreasing or increasing the injector
pulse width as necessary. If the Bank 2 HO2S 1 voltage
remains excessively high for an extended period of time,
DTC P0152 will be set.
Conditions for Setting the DTC

No related DTCs.

The engine is operating in ªclosed loop.º

The engine coolant temperature is above 60
C
(140
F).

ªClosed loopº commanded air/fuel ratio between 14.5
and 14.8.

Throttle angle between 3% and 19%.

Bank 2 HO2S 1 signal voltage remains above 952 mV
during normal ªclosed loopº operation for a total of 77
seconds over a 90-second period.
OR
Bank 2 HO2S 1 signal voltage remains above 500 mV
during deceleration fuel cutoff mode operation for up to
3 seconds.
Action Taken When the DTC Sets

The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.

The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.

ªOpen loopº fuel control will be in effect.
Conditions for Clearing the MIL/DTC

DTC P0152 can be cleared by using Tech 2 ªClear Infoº
function or by disconnecting the PCM battery feed.
Diagnostic Aids
Check for the following conditions:

Fuel pressure ± The system will go rich if pressure is
too high. The PCM can compensate for some
increase. However, if fuel pressure is too high, a DTC
P0152 may be set. Refer to
Fuel System Diagnosis.

Rich injector(s) ± Perform ªInjector Balance Test.º

Leaking injector ± Refer to
Fuel System Diagnosis.

Evaporative emissions (EVAP) system ± Check the
canister for fuel saturation. If the canister is full of fuel,
check EVAP control system components and hoses.
Refer to
Evaporative Emission (EVAP) Control
System.

6E±152
ENGINE DRIVEABILITY AND EMISSIONS

MAF sensor ± The system can go rich if the MAF
sensor signal indicates an engine airflow
measurement that is not correct. Disconnect the MAF
sensor to see if rich condition is corrected. If so,
replace MAF sensor.

Check for leaking fuel pressure regulator diaphragm by
checking vacuum line to regulator for the presence of
fuel. There should be no fuel in the vacuum line.

TP sensor ± An intermittent TP sensor output will
cause the system to go rich, due to a false indication
of the engine accelerating.

Shorted Heated Oxygen Sensor (HO2S)± If the HO2S
is internally shorted, the HO2S voltage displayed on
Tech 2 will be over 1 volt. Try disconnecting the
affected HO2S with the key ªON,º engine ªOFF.º If the
displayed HO2S voltage changes from over 1000 mV
to around 450 mV, replace the HO2S. Silicon
contamination of the HO2S can cause a high HO2S
voltage to be indicated. This condition is indicated by
powdery white deposit on the portion of the HO2S
exposed to the exhaust stream. If contamination is
noticed, replace the affected HO2S.

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
switch between the rich and lean thresholds can also
cause the condition. Operate the vehicle while
monitoring the HO2S voltage with Tech 2. If the HO2S
is limited within a range between 300 mV to 600 mV,
check the HO2S signal circuit wiring and associated
terminal connections.

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 P0152 failing during deceleration fuel cutoff
mode operation may indicate a condition described
in the ªDiagnostic Aidsº above. If the DTC P0152
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.
DTC P0152 ± HO2S Circuit High Voltage Bank 2 Sensor 1

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Install Tech 2.
2. Engine is at operating temperature.
3. Operate the vehicle within the parameters specified
under ªConditions for Setting the DTCº criteria
included in Diagnostic Support.
4. Using Tech 2, monitor Bank 2 HO2S 1 voltage.
Does the Bank 2 HO2S 1 voltage remain above the
specified value?
952 mV
(500 mV in
deceleration
fuel cut-off
mode)
Go to Step 4Go to Step 3
31. Ignition ªON.º
2. Review and record Tech 2 Failure Records data.
3. Operate the vehicle within Failure Records
conditions as noted.
4. Using Tech 2, monitor ªSpecific DTCº info for DTC
P0152 until the DTC P0152 test runs.
5. Note the test result.
Does Tech 2 indicate DTC P0152 failed this ignition?
ÐGo to Step 4
Refer to
Diagnostic
Aids
41. Ignition ªOFF.º
2. Disconnect Bank 2 HO2S 1.
3. Ignition ªON.º
4. At HO2S Bank 2 Sensor 1 connector (PCM side)
use a DVM to measure voltages at the high and low
signal terminals.
Are the voltages in the specified range?
3-4 VGo to Step 5Go to Step 6
5Repair short to voltage in signal circuit.
Is the action complete?
ÐVerify repairÐ

6E±155 ENGINE DRIVEABILITY AND EMISSIONS

Mass air flow is between 2 g/second and 200 g/second.

Ignition voltage is above 9.5 volts.

Fuel system is in ªclosed loop.º
Action Taken When the DTC Sets

The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.

The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC

DTC P0171 can be cleared by using the Tech 2 ªClear
Infoº function or by disconnecting the PCM battery
feed.
Diagnostic Aids
Check for the following conditions:

Poor connection at PCM ± Inspect harness connectors
for backed-out terminals, improper mating, broken
locks, improperly formed or damaged terminals, and
poor terminal-to-wire connection.
Damaged harness ± Inspect the wiring harness for
damage. If the harness appears to be OK, observe the
Bank 1 HO2S 1 display on the Tech 2 while moving
connectors and wiring harnesses related to the engine
harness. A change in the display will indicate the
location of the fault.
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.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. DTCs other than P0171 and P0174 may indicate a
condition present which may cause a lean condition.
If this is the case, repairing the condition which
caused the other DTC will most likely correct the
DTC P0171/P0174.
4. If the DTC P0171 test passes while the Failure
Records conditions are being duplicated, the lean
condition is intermittent. Refer to
Diagnostic Aids or
Symptoms for additional information on diagnosing
intermittent problems.

6E±156
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0171 ± Fuel Trim System Lean Bank 1

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
2Are any DTCs set other than P0171 and P0174?
Ð
Go to the
applicable
DTC charts
and repair the
other DTCs
before
proceeding
with this chart
Go to Step 3
31. Start the engine and operate the vehicle in ªclosed
loop.º
2. Observe the ªBANK 1 L.T. FUEL TRIMº display on
the Tech 2.
Is the displayed value greater than the specified value?
L.T. Fuel
Trim: +20%
Go to Step 5Go to Step 4
41. Review and record the Tech 2 Failure Records data.
2. Clear the DTC P0171/P0174 and operate the
vehicle to duplicate the Failure Records conditions.
3. Monitor the Tech 2 ªSpecific DTCº info for DTC
P0171 while operating the vehicle to duplicate the
Failure Records conditions.
4. Continue operating the vehicle until the DTC P0171
test runs and note the test result.
Does the Tech 2 indicate DTC P0171 failed this
ignition?
ÐGo to Step 5
The lean
condition is
not present.
If a
driveability
symptom still
exists, refer
to
Symptoms
section.
5Was DTC P0174 also set?ÐGo to Step 6Go to Step 15
6Visually and physically inspect the vacuum hoses for
disconnects, splits, kinks, improper routing and
improper connections and repair any problem found.
Did your inspection reveal a problem requiring repair?
ÐVerify repairGo to Step 7
7Visually and physically inspect the crankcase
ventilation valve for proper installation and repair any
problem found (refer to
Crankcase Ventilation
System
).
Did your inspection reveal a problem requiring repair?
ÐVerify repair Go to Step 8
81. Inspect the MAF sensor inlet screen for damage or
for the presence of foreign objects which may
partially block the air flow sample through the MAF
sensor.
2. Correct any problem that is found as necessary.
Did your inspection of the MAF sensor reveal a
condition requiring repair?
ÐVerify repairGo to Step 9
9Start the engine and note the idle quality.
Is a high or unsteady idle being experienced?
ÐGo to Step 10Go to Step11
101. Visually and physically inspect the throttle body,
intake manifold, EGR valve and the EGR feed pipe
for vacuum leaks.
2. Repair any vacuum leaks as necessary.
Did your inspection reveal a vacuum leak?
ÐVerify repair Go to Step 11

6E±157 ENGINE DRIVEABILITY AND EMISSIONS
DTC P0171 ± Fuel Trim System Lean Bank 1

 
StepNo Ye s Value(s) Action
11Check the fuel for excessive water, alcohol, or other
contaminants (see
Diagnosis in Engine Fuel for the
procedure) and correct the contaminated fuel condition
if present (see
Engine Fuel).
Was the fuel contaminated?
ÐVerify repair Go to Step 12
121. Visually and physically inspect the PCM injector
grounds, power grounds and sensor grounds to
ensure that they are clean, tight, and in their proper
locations.
2. If a faulty ground condition is present, correct it as
necessary.
Did your inspection reveal a condition requiring repair?
ÐVerify repairGo to Step 13
131. Disconnect the MAF sensor electrical connector.
2. Operate the vehicle in ªclosed loopº while
monitoring the ªBANK 1 S.T. FUEL TRIMº displayed
on the Tech 2.
Does ªBANK 1 S.T. FUEL TRIMº value decrease to
near the specified value?
0%Go to Step 19Go to Step 14
14Perform the procedure in the ªFuel System Pressure
Testº and repair fuel system problem if necessary.
Did Fuel System Pressure Test isolate a condition
requiring repair?
ÐVerify repairGo to Step 15
151. Visually and physically inspect the intake manifold,
injector O-rings, EGR adapter, EGR valve and the
EGR feed pipes for vacuum leaks.
2. Repair any problem that is found.
Did your inspection reveal a problem?
ÐVerify repairGo to Step 16
16Visually and physically inspect the Bank 1 exhaust
manifold for leaks and loose or missing hardware and
correct any problem found.
Did your inspection reveal a problem?
ÐVerify repairGo to Step 17
17Perform the ªInjector Balance Test,º and correct any
problem found (refer to
Fuel Metering System).
Did Injector Balance Test isolate a problem?
ÐVerify repairGo to Step 18
181. Visually and physically inspect the Bank 1 HO2S 1
to ensure that it is installed securely and that the
Bank 1 HO2S 1 pigtail and wiring harness are not
contacting the exhaust or otherwise damaged.
2. If a problem is found, correct it as necessary.
Did your inspection reveal a problem?
ÐVerify repair
Refer to
Diagnostic
Aids
19Replace the MAF sensor.
Is the action complete?
ÐVerify repairÐ

6E±159 ENGINE DRIVEABILITY AND EMISSIONS

Vehicle speed is below 136 km/h (85 mph).

Engine speed is between 400 and 6,000 RPM.

Barometric pressure is greater than 72.5 kPa.

Mass air flow is between 2 g/second and 200 g/second.

Ignition voltage is above 9.5 volts.

Fuel system is in ªclosed loop.º
Action Taken When the DTC Sets

The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.

The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC

DTC P0172 can be cleared by using the Tech 2 ªClear
Infoº function or by disconnecting the PCM battery
feed.
Diagnostic Aids
Check for the following conditions:

Poor connection at PCM ± Inspect harness connectors
for backed-out terminals, improper mating, broken
locks, improperly formed or damaged terminals, and
poor terminal-to-wire connection.
Damaged harness ± Inspect the wiring harness for
damage. If the harness appears to be OK, observe the
Bank 1 HO2S 1 display on the Tech 2 while moving
connectors and wiring harnesses related to the engine
harness. A change in the display will indicate the
location of the fault.
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.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. DTCs other than P0172 and P0175 may indicate a
condition present which may cause a lean condition.
If this is the case, repairing the condition which
caused the other DTC will most likely correct the
DTC P0172/P0175.
4. If the DTC P0172 test passes while the Failure
Records conditions are being duplicated, the rich
condition is intermittent. Refer to
Diagnostic Aids or
Symptoms for additional information on diagnosing
intermittent problems.

6E±160
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0172 ± Fuel Trim System Rich Bank 1

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
2Are any DTCs set other than P0172 and P0175?
Ð
Go to the
applicable
DTC charts
and repair the
other DTCs
before
proceeding
with this chart
Go to Step 3
31. Start the engine and operate the vehicle in ªclosed
loop.º
2. Observe ªB1 Long Term Fuel Trimº display on the
Tech 2.
Is the displayed value more negative than the specified
value?
L.T. Fuel
Trim: ±15%
(auto. trans.)
OR ±12%
(man. trans.)
Go to Step 5Go to Step 4
41. Review and record the Tech 2 Failure Records data.
2. Clear the DTC P0172/P0175 and operate the
vehicle to duplicate the Failure Records conditions.
3. Monitor the Tech 2 ªDTCº info for DTC P0172 while
operating the vehicle to duplicate the Failure
Records conditions.
4. Continue operating the vehicle until the DTC P0172
test runs and note test result.
Does the Tech 2 indicate DTC P0172 failed this
ignition?
ÐGo to Step 5
The rich
condition is
not present.
If a
driveability
symptom still
exists, refer
to
Symptoms.
5Is DTC P0175 also set?ÐGo to Step 6Go to Step 15
6Visually and physically inspect the air filter element and
replace it if necessary.
Did the air filter require replacement?
ÐVerify repairGo to Step 7
7Visually and physically inspect the air intake duct for
collapse or restriction and repair if necessary.
Did your inspection reveal a condition requiring repair?
ÐVerify repairGo to Step 8
8Inspect the MAF sensor inlet screen for damage or for
the presence of foreign objects which may partially
block air flow through the screen and correct any
problem found.
Did your inspection of the MAF sensor reveal a
condition requiring repair or replacement?
ÐVerify repairGo to Step 9
9Start the engine and note the idle quality.
Is a low or unsteady idle being experienced?
ÐGo to Step 10Go to Step 11
101. Ignition ªOFF.º
2. Physically inspect the throttle body bore, throttle
plate, and IAC passages for coking and foreign
objects.
3. If a problem was found, repair as necessary.
Did your inspection reveal a condition requiring repair?
ÐVerify repairGo to Step 11

6E±161 ENGINE DRIVEABILITY AND EMISSIONS
DTC P0172 ± Fuel Trim System Rich Bank 1

 
StepNo Ye s Value(s) Action
111. Disconnect the vacuum hose from the fuel pressure
regulator and inspect the hose for the presence of
fuel.
2. If fuel is present in the vacuum hose, replace the
fuel pressure regulator (refer to
Fuel Metering
System
).
Did the fuel pressure regulator require replacement?
ÐVerify repairGo to Step 12
12Ignition ªON,º engine ªOFF,º monitor the TP Angle
display on the Tech 2 while slowly depressing the
accelerator pedal.
Does the TP Angle display increase steadily and
evenly from minimum value at closed throttle to
maximum value at wide-open throttle?
Minimum 0%
Maximum
100%
Go to Step 13Go to Step 18
131. Disconnect the MAF sensor electrical connector.
2. Operate the vehicle in ªclosed loopº while
monitoring the ªBANK 1 L.T. FUEL TRIMº and
ªBANK 1 S. T. FUEL TRIMº display on the Tech 2.
Did both values change to near the specified value?
0%Go to Step 19Go to Step 14
141. Perform ªFuel System Pressure Test.º
2. If Fuel System Pressure Test isolates a problem,
repair as necessary (refer to
Engine Fuel or Fuel
Metering System
).
Did the Fuel System Pressure Test isolate a problem
requiring repair?
ÐVerify repairGo to Step 16
15Replace the PCM.
IMPORTANT:The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?ÐVerify repairÐ
161. Perform the ªInjector Balance Test.º
2. If Injector Balance Test isolates a problem, repair as
necessary (refer to
Fuel Metering System).
Did the Injector Balance Test isolate a problem
requiring repair?
ÐVerify repair Go to Step 17
171. Remove and visually/physically inspect the Bank 1
HO2S 1 for silicon contamination. This will be
indicated by a powdery white deposit on the portion
of the HO2S that is exposed to the exhaust stream.
2. If contamination is evident on the Bank 1 HO2S 1,
replace the contaminated sensors.
Did the sensor require replacement?
ÐVerify repair
Refer to
Diagnostic
Aids
181. Check the TP sensor mounting screws and tighten
or replace them as necessary if they are loose or
missing.
2. If the screws are OK, replace the TP sensor.
Is the action complete?
ÐVerify repairÐ
19Replace the MAF sensor.
Is the action complete?
ÐVerify repairÐ