Isuzu Trooper (1998-2002 year). Manual - part 606

6E–72

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0122 (Flash DTC 21) 

AP Sensor Low Voltage

060RW134

Circuit Description

The accelerator position (AP) sensor circuit provides a
voltage signal that changes relative to throttle blade
angle.
The AP signal is used by the Engine Control Module ECM
for fuel volume control and many of the ECM-controlled
outputs.

Action Taken When the DTC Sets

D

The ECM 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

D

DTC P0122 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the ECM battery
feed.

Diagnostic Aids

Check for the following conditions:

D

Poor connection at ECM – Inspect harness connectors
for backed-out terminals, improper mating, broken
locks, improperly formed or damaged terminals, and
poor terminal-to-wire connection.

D

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.

DTC P0122 –AP Sensor Low Voltage

 

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to 

Step 2

Go to 

OBD

System

Check

2

Check the AP sensor signal circuit.

Was the AP sensor signal circuit open or darmage?

—

Replace the

APS circuit

Go to 

Step 3

6E–73

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

DTC P0122 –AP Sensor Low Voltage

  (Cont'd)

Step

No

Yes

Value(s)

Action

3

1. Ignition “ON,” engine “OFF.”
2. With the throttle closed, observe the “AP Sensor”

display on the Tech 2.

Is the “AP Sensor” below the specified value?

0.1 V

Go to 

Step 5

Go to 

Step 4

4

1. Ignition “ON,” engine “OFF.”
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 “DTC” info for DTC

P0122.

Does the Tech 2 indicate DTC P0122 failed?

—

Go to 

Step 5

Refer to

Diagnostic

Aids

5

1. Ignition “OFF.”
2. Disconnect the AP sensor electrical connector.
3. Jumper the 5 volt reference “J2” circuit and the AP

signal together at the AP sensor harness connector.

4. Ignition “ON.”
Observe the “AP Sensor” display on the Tech 2.

Is the “AP Sensor” at the specified value?

5 V

Go to 

Step 11

Go to 

Step 6

6

1. Disconnect jumper.
2. Connect a test light between B+ and the AP sensor

signal circuit at the AP sensor harness connector.

Observe the “AP Sensor” display on the Tech 2.

Is the “AP Sensor” at the specified value?

5 V

Go to 

Step 7

Go to 

Step 9

7

1. Ignition “OFF.”
2. Disconnect the ECM and check the 5 volt reference

“A” circuit for an open or short to ground.

3. If the 5 volt reference “J2” circuit is open or shorted

to ground, repair it as necessary.

Was the 5 volt reference “J2” circuit open or shorted to
ground?

—

Verify repair

Go to 

Step 8

8

Check the 5 volt reference “J2” circuit for a poor
connection at the ECM and replace the terminal if
necessary.

Did the terminal require replacement?

—

Verify repair

Go to 

Step 13

9

1. Ignition “OFF.”
2. Disconnect the ECM, and check the AP signal

circuit for an open, short to ground, or short to the
sensor ground circuit.

3. If the AP sensor signal circuit is open or shorted to

ground, repair it as necessary.

Was the AP signal circuit open or shorted to ground?

—

Verify repair

Go to 

Step 10

10

Check the AP sensor signal circuit for a poor
connection at the ECM and replace the terminal if
necessary.

Did the terminal require replacement?

—

Verify repair

Go to 

Step 13

11

Check the AP sensor signal circuit for a poor
connection at the AP sensor and replace the terminal if
necessary.

Did the terminal require replacement?

—

Verify repair

Go to 

Step 12

6E–74

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

DTC P0122 –AP Sensor Low Voltage

  (Cont'd)

Step

No

Yes

Value(s)

Action

12

Replace the AP sensor.

Is the action complete?

—

Verify repair

—

13

Replace the ECM (Refer to the Data Programming in
Case of ECM change).

Is the action complete?

—

Verify repair

—

6E–75

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0123 (Flash DTC 21)

 AP Sensor High Voltage

060RW134

Circuit Description

The accelerator position (AP) sensor circuit provides a
voltage signal that changes relative to throttle blade
angle.
The TP signal is one of the most important inputs used by
the Engine Control Module ECM for fuel volume control
and many of the ECM-controlled outputs.

Action Taken When the DTC Sets

D

The ECM 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

D

DTC P0123 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the ECM battery
feed.

Diagnostic Aids

Check for the following conditions:

D

Poor connection at ECM – Inspect harness connectors
for backed-out terminals, improper mating, broken

locks, improperly formed or damaged terminals, and
poor terminal-to-wire connection.

D

Damaged harness – Inspect the wiring harness for
damage.  If the harness appears to be OK, observe the
AP 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.

D

Faulty AP sensor – With the ignition key “ON,” engine
“OFF,” observe the AP 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 AP 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.
8. Components that share the AP sensor 5 volt reference
“A” circuit include the following device: