1998 ISUZU TROOPER Service Repair Manual

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Page 1249 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±132
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0121 ±TP System Performance
StepNo Ye s Value(s) Action
10Check the following items:
1. TP signal circuit or 5 volt reference ªAº circuit fo

Page 1250 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±133 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0122 TP Sensor Circuit Low Voltage
D06RW028
Circuit Description
The throttle position (TP) sensor circuit provides a voltage
si

6E±133 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0122 TP Sensor Circuit Low Voltage
D06RW028
Circuit Description
The throttle position (TP) sensor circuit provides a voltage
signal that changes relative to throttle blade angle. The
signal voltage will vary from below 0.6 volts at closed
throttle to about 4.5 volts at wide open throttle (WOT).
The TP signal is used by the powertrain control module
(PCM) for fuel control and many of the PCM±controlled
outputs.
Conditions for Setting the DTC
The ignition is ªON.º
TP sensor signal voltage is less than 0.22 volt for a total
of 0.78 second over a 1.5-second period.
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.
The PCM will use a default throttle position based on
mass air flow and RPM.
Conditions for Clearing the MIL/DTC
DTC P0122 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:
Check intermittent codes.
The TP sensor shares a 5 Volt reference with the EGR
position sensor. Check the 5 Volt reference if these
DTCs are also set.
The TP sensor shares a ground with the IAT sensor,
the EGR position sensor.
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
throttle position display on the Tech 2 while moving
connectors and wiring harnesses related to the TP
sensor. A change in the display will indicate the
location of the fault.
If DTC P0122 cannot be duplicated, the information
included in the Failure Records data can be useful in
determining vehicle mileage since the DTC was last set.

Page 1251 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±134
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0122 ±TP Sensor Circuit Low Voltage
StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
S

6E±134
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0122 ±TP Sensor Circuit Low Voltage
StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Ignition ªON,º engine ªOFF.º
2. With the throttle closed, observe the ªTP Sensorº
display on the Tech 2.
Is the ªTP Sensorº below the specified value?
0.22 VGo to Step 4Go to Step 3
31. Ignition ªON,º engine ªOFF.º
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 the ªDTCº info for DTC
P0122.
Does the Tech 2 indicate DTC P0122 failed?
ÐGo to Step 4
Refer to
Diagnostic
Aids
41. Ignition ªOFF.º
2. Disconnect the TP sensor electrical connector.
3. Jumper the 5 volt reference ªAº circuit and the TP
signal together at the TP sensor harness connector.
4. Ignition ªON.º
Observe the ªTP Sensorº display on the Tech 2.
Is the ªTP Sensorº at the specified value?
5 VGo to Step 10Go to Step 5
51. Disconnect jumper.
2. Connect a test light between B+ and the TP sensor
signal circuit at the TP sensor harness connector.
Observe the ªTP Sensorº display on the Tech 2.
Is the ªTP Sensorº at the specified value?
5 VGo to Step 6Go to Step 8
61. Ignition ªOFF.º
2. Disconnect the PCM and check the 5 volt reference
ªAº circuit for an open or short to ground.
3. If the 5 volt reference ªAº circuit is open or shorted to
ground, repair it as necessary.
Was the 5 volt reference ªAº circuit open or shorted to
ground?
ÐVerify repairGo to Step 7
7Check the 5 volt reference ªAº circuit for a poor
connection at the PCM and replace the terminal if
necessary.
Did the terminal require replacement?
ÐVerify repairGo to Step 12
81. Ignition ªOFF.º
2. Disconnect the PCM, and check the TP signal
circuit for an open, short to ground, or short to the
sensor ground circuit.
3. If the TP sensor signal circuit is open or shorted to
ground, repair it as necessary.
Was the TP signal circuit open or shorted to ground?
ÐVerify repairGo to Step 9
9Check the TP sensor signal circuit for a poor
connection at the PCM and replace the terminal if
necessary.
Did the terminal require replacement?
ÐVerify repairGo to Step 12

Page 1252 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±135 ENGINE DRIVEABILITY AND EMISSIONS
DTC P0122 ±TP Sensor Circuit Low Voltage
StepNo Ye s Value(s) Action
10Check the TP sensor signal circuit for a poor
connection at the TP sensor a

Page 1253 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±136
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0123 TP Sensor Circuit High Voltage
D06RW028
Circuit Description
The throttle position (TP) sensor circuit provides a voltage

6E±136
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0123 TP Sensor Circuit High Voltage
D06RW028
Circuit Description
The throttle position (TP) sensor circuit provides a voltage
signal that changes relative to throttle blade angle. The
signal voltage will vary from about 0.6 volts at closed
throttle to about 4.5 volts at wide open throttle (WOT).
The TP signal is one of the most important inputs used by
the powertrain control module (PCM) for fuel control and
many of the PCM-controlled outputs.
Conditions for Setting the DTC
The ignition is ªON.º
TP sensor signal voltage is greater than 4.88 volts for
a total of 0.78 second over a 1.5-second period.
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.
The PCM will use a default throttle position based on
mass air flow and RPM.
Conditions for Clearing the MIL/DTC
DTC P0123 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:Check intermittent codes.
The TP sensor shares a 5 Volt reference with the EGR
position sensor. Check the 5 Volt reference if these
DTCs are also set.
The TP sensor shares a ground with the IAT sensor
and the EGR position sensor. Check the ground if
these other DTCs are also set.
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
TP sensor display on the Tech 2 while moving
connectors and wiring harnesses related to the TP
sensor. A change in the display will indicate the
location of the fault.
Faulty TP sensor ± With the ignition key ªON,º engine
ªOFF,º observe the TP sensor display on the Tech 2
while slowly depressing the accelerator to wide open
throttle. If a voltage over 4.88 volts is seen at any point
in normal accelerator travel, replace the TP sensor.
If DTC P0123 cannot be duplicated, the information
included in the Failure Records data can be useful in
determining vehicle mileage since the DTC was last set.
Test Description
Number (s) below refer to the step number(s) on the
Diagnostic Chart.
7. Components that share the TP sensor 5 volt reference
ªAº circuit include the following device:
EGR valve

Page 1254 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±137 ENGINE DRIVEABILITY AND EMISSIONS
Disconnect the component while observing the TP
sensor display on the Tech 2. If the reading
changes drastically when this component isdisconnected, replace

6E±137 ENGINE DRIVEABILITY AND EMISSIONS
Disconnect the component while observing the TP
sensor display on the Tech 2. If the reading
changes drastically when this component isdisconnected, replace the component that affected
the reading.
DTC P0123 ± TP Sensor Circuit High Voltage
StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Ignition ªON,º engine ªOFF.º
2. With the throttle closed, observe the ªTP Sensorº
display on the Tech 2.
Is the ªTP Sensorº above the specified value?
4.88 VGo to Step 4Go to Step 3
31. Ignition ªON,º engine ªOFF.º
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 ªSpecific DTCº info for DTC
P0123.
Does the Tech 2 indicate DTC P0123 failed.
ÐGo to Step 4
Refer to
Diagnostic
Aids
41. Disconnect the TP sensor electrical connector.
2. Observe the ªTP Sensorº display on the Tech 2.
Is the ªTP Sensorº near the specified value?
0 VGo to Step 5Go to Step 6
5Probe the sensor ground circuit at the TP sensor
harness connector with a test light connected to B+.
Is the test light ªON?º
ÐGo to Step 7Go to Step 10
61. Ignition ªOFF,º disconnect the PCM.
2. Ignition ªON,º engine ªOFF.º
3. Check for a short to voltage on the TP sensor signal
circuit.
4. If the TP sensor signal circuit is shorted, repair it as
necessary.
Was the TP sensor signal circuit shorted?
ÐVerify repairGo to Step 12
71. Ignition ªON.º
2. Monitor the ªTP Sensorº Tech 2 display while
disconnecting each of the components that share
the 5 volt reference ªAº circuit (one at a time).
3. If the ªTP Sensorº Tech 2 display changes, replace
the component that caused the display to change
when disconnected.
Does disconnecting any of these components cause
the ªTP Sensorº display to change?
ÐVerify repairGo to Step 8
81. Ignition ªOFF,º disconnect the PCM.
2. Ignition ªON,º engine ªOFF.º
3. Check for a short to B+ on the 5 volt reference ªAº
circuit.
4. If the 5 volt reference ªAº circuit is shorted, repair it
as necessary.
Was the 5 volt reference ªAº circuit shorted?
ÐVerify repairGo to Step 9
9Check for poor electrical connections at the TP sensor
and replace terminals if necessary.
Did any terminals require replacement?
ÐVerify repairGo to Step 11

Page 1255 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±138
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0123 ± TP Sensor Circuit High Voltage
StepNo Ye s Value(s) Action
101. Ignition ªOFF.º
2. Disconnect the PCM, and check for an open sensor
g

Page 1256 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±139 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0131 HO2S Circuit Low Voltage Bank 1
Sensor 1
060RW236
Circuit Description
The powertrain control module (PCM) supplies a bias

6E±139 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0131 HO2S Circuit Low Voltage Bank 1
Sensor 1
060RW236
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 350 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 injector
pulse width as necessary. If the Bank 1 HO2S 1 voltage
remains excessively low for an extended period of time,
DTC P0131 will be set.
Conditions for Setting the DTC
No related DTCs.
Vehicle is operating in ªclosed loop.º
Engine coolant temperature is above 60C (140F).
ªClosed loopº commanded air/fuel ratio is between
14.5 and 14.8.
Throttle angle is between 3% and 19%.
Bank 1 HO2S 1 signal voltage remains below 22 mV
during normal ªclosed loopº operation for a total of 77
seconds over a 90-second period of time.
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 P0131 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:
Heated oxygen sensor wiring ± The sensor pigtail may
be routed incorrectly and contacting the exhaust
system.
Poor PCM to engine block grounds.
Fuel pressure ± The system will go lean if pressure is
too low. The PCM can compensate for some
decrease. However, If fuel pressure is too low, a DTC
P0131 may be set. Refer to
Fuel System Diagnosis.
Lean injector(s) ± Perform ªInjector Balance Test.º
Vacuum leaks ± Check for disconnected or damaged
vacuum hoses and for vacuum leaks at the intake
manifold, throttle body, EGR system, and PCV system.
Exhaust leaks ± An exhaust leak may cause outside air
to be pulled into the exhaust gas stream past the

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