Isuzu Trooper (1998-2002 year). Manual - part 605

6E–68

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Verifies that the fault is present.

3. If DTC P0118 can be repeated only by duplicating

the Failure Records conditions, refer to the
“Temperature vs. Resistance Value” table. The
table may be used to test the ECT sensor at various
temperatures to evaluate the possibility of a
“shifted” sensor that may be shorted above or below
a certain temperature. If this is the case, replace
the ECT sensor. If the ECT sensor appears to be
OK, the fault is intermittent; refer to

Diagnostic Aids.

Engine Coolant Temperature Sensor

Ohms

Temperature vs. Resistance Values

(approximate)

176

332

2796

4450

DTC P0118 – ECT Sensor High Voltage

Step

Action

Value(s)

Yes

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

—

Go to

Step 2

Go to

OBD

System

Check

1. Ignition “ON,” engine “OFF.”
2. Observe the “Eng Cool Temp” display on the Tech 2.

Is the “Eng Cool Temp” below the specified value?

–39

(–38

Go to

Step 4

Go to

Step 3

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

P0118.

Does the Tech 2 indicate DTC P0118 failed?

—

Refer to

Test

Description

Refer to

Diagnostic

Aids

1. Disconnect the ECT sensor electrical connector.
2. Jumper the ECT signal circuit and the sensor

ground circuit together at the ECT sensor harness
connector.

3. Observe the “Eng Cool Temp” display on the Tech 2.

Is the “Eng Cool Temp” at the specified value?

140

(284

Go to

Step 6

Go to

Step 5

1. Jumper the ECT signal circuit at the ECT sensor

harness connector to chassis ground.

2. Observe the “Eng Cool Temp” display on the Tech 2.

Is the “Eng Cool Temp” at the specified value?

140

(284

Go to

Step 7

Go to

Step 8

Check for poor connections at the ECT sensor and
replace terminals if necessary.

Did any terminals require replacement?

—

Verify repair

Go to

Step 10

1. Ignition “OFF.”
2. Disconnect the ECM, and check the ECT sensor

ground circuit for an open.

3. If the ECT sensor ground circuit is open, repair it as

necessary.

Was the ECT sensor ground circuit open?

—

Verify repair

Go to

Step 9

6E–69

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

DTC P0118 – ECT Sensor High Voltage

(Cont'd)

Step

Yes

Value(s)

Action

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

circuit for an open.

3. If the ECT sensor signal circuit is open, repair it as

necessary.

Was the ECT signal circuit open?

—

Verify repair

Go to

Step 9

Check for a poor sensor ground or ECT signal circuit
terminal connection at the ECM and replace
terminal(s) if necessary.

Did any of the terminals need to be replaced?

—

Verify repair

Go to

Step 11

Replace the ECT sensor.

Is the action complete?

—

Verify repair

—

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

Is the action complete?

—

Verify repair

—

6E–70

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0121 (Flash DTC 33)

AP Sensor Rationality

060RW134

Circuit Description

The accel position (AP) sensor circuit provides a voltage
signal that changes relative to throttle blade angle.
The AP 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. If the ECM
detects an out-of-range condition, DTC P0121 will set.

Action Taken When the DTC Sets

The ECM will illuminate the malfunction indicator lamp
(MIL) after fault is detected.

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

DTC P0121 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:

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.

Damaged harness – Inspect the wiring harness for
damage. If the harness appears to be OK, observe the
ECT display on the Tech 2 while moving connectors
and wiring harnesses related to the sensor. A change
in the display will indicate the location of the fault.

If DTC P0121 cannot be duplicated, the information
included in the Failure Records data can be useful in
determining vehicle mileage since the DTC was last set.

6E–71

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

DTC P0121 –AP Sensor Rationality

Step

Action

Value(s)

Yes

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

—

Go to

Step 2

Go to

OBD

System

Check

Check the Idle SW.

Was the Idle SW circuit open or darmage?

—

Replace the

Idle SW

circuit

Go to

Step 3

Observe the AP angle reading on the Tech 2 while
slowly opening the throttle.

Does the AP angle increase steadily and evenly from
the closed throttle value to the wide open throttle
value?

Closed

throttle = 0%

Wide open

throttle =

100%

Refer to

Diagnostic

Aids

Go to

Step 4

1. Disconnect the AP sensor.
2. Observe the AP sensor reading on the Tech 2.

Is the AP sensor reading near the specified value?

0 V

Go to

Step 5

Go to

Step 6

1. Connect a test light between the 5 volt reference

“J2” circuit and the AP sensor signal circuit at the AP
sensor harness connector.

2. Observe the AP sensor reading on the Tech 2.

Is the AP sensor reading at the specified value?

5 V

Go to

Step 8

Go to

Step 7

Check the following items:

1. AP signal circuit for a short to voltage.
2. AP sensor ground circuit for high resistance

between the ECM and the AP sensor.

3. AP sensor ground circuit for a poor connection.
4. If a problem is found, repair wiring harness as

necessary.

Was a problem found?

—

Verify repair

Go to

Step 9

Check the following items:

1. AP signal circuit or 5 volt reference “J2” circuit for a

poor connection.

2. AP signal circuit or 5 volt reference “J2” circuit for

high resistance between the ECM and the AP
sensor.

3. If a problem is found, repair wiring harness as

necessary.

Was a problem found?

—

Verify repair

Go to

Step 9

Replace the AP sensor.

Is the action complete?

—

Verify repair

—

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

Is the action complete?

—

Verify repair

—

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