Isuzu Trooper (1998-2002 year). Manual - part 603

6E–60

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0112 (Flash DTC 23)

IAT Sensor Circuit Low Voltage

060RW129

Circuit Description

The Intake air temperature (IAT) sensor is a thermistor
which measures the temperature of the air entering the
engine. The Engine Control Module ECM applies 5 volts
through a pull-up resistor to the IAT sensor. When the
intake air is cold, the sensor resistance is high and the
ECM will monitor a high signal voltage on the IAT signal
circuit. If the intake air is warm, the sensor resistance is
lower, causing the ECM to monitor a lower voltage. DTC
P0112 will set when the ECM detects an excessively low
signal voltage on the Intake air temperature sensor signal
circuit.

Action Taken When the DTC Sets

The ECM will illuminate the malfunction indicator lamp
(MIL) the first time the 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 P0112 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
IAT display on the Tech 2 while moving connectors and
wiring harnesses related to the IAT sensor. A change
in the IAT display will indicate the location of the fault.

If DTC P0112 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–61

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 P0112 can be repeated only by duplicating

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

Diagnostic Aids.

Intake Air Temperature Sensor

Ohms

Temperature vs. Resistance Values

(approximate)

2796

4450

7280

DTC P0112 – IAT Sensor Low 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. Using a Tech 2, monitor the intake air temperature

(IAT).

Is the intake air temperature greater than the specified
value?

148

(283

Go to

Step 4

Go to

Step 3

1. Ignition “ON,” engine “OFF.” Review and record

Tech 2 Failure Records data.

2. Operate the vehicle within Failure Records

conditions as noted.

3. Using a Tech 2, monitor the “ DTC” info for DTC

P0112.

Does the Tech 2 indicate DTC P0112 failed this
ignition?

—

Refer to

Test

Description

Refer to

Diagnostic

Aids

1. Ignition “OFF.”
2. Disconnect the IAT sensor electrical connector.
3. Ignition “ON.”
4. Observe the manifold air temperature on the Tech 2.

Is the manifold air temperature below the specified
value?

–38

(–36

Go to

Step 6

Go to

Step 5

1. Ignition “OFF.”
2. Disconnect the ECM electrical connectors.
3. Check the IAT sensor signal circuit for a short to

ground.

Is the IAT sensor signal circuit shorted to ground?

—

Verify repair

Go to

Step 7

Replace the IAT 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–62

4JX1–TC ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P0113 (Flash DTC 23)

IAT Sensor Circuit High Voltage

060RW129

Circuit Description

The intake air temperature (IAT) sensor is a thermistor
which measures the temperature of the air entering the
engine. The Engine Control Module ECM applies 5 volts
through a pull-up resistor to the IAT sensor. When the
intake air is cold, the sensor resistance is high and the
ECM will monitor a high signal voltage on the IAT signal
circuit. If the intake air is warm, the sensor resistance is
lower causing the ECM to monitor a lower voltage. DTC
P0113 will set when the ECM detects an excessively high
signal voltage on the intake air temperature sensor signal
circuit.

Action Taken When the DTC Sets

The ECM will illuminate the malfunction indicator lamp
(MIL) the first time the 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 P0113 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.

If DTC P0113 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–63

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 P0113 can be repeated only by duplicating

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

Diagnostic Aids.

Manifold Air Temperature Sensor

Ohms

Temperature vs. Resistance Values

(approximate)

2796

4450

7280

DTC P0113 –IAT Sensor Circuit 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

Ignition “ON,” engine “OFF.” Observe the “Intake Air
Temp” display on the Tech 2.

Is the “Intake Air Temp” below the specified value?

–38

(–36

Go to

Step 4

Go to

Step 3

1. Ignition “ON,” engine “OFF.”
2. Review and record Tech 2 Failure Records data

parameters.

3. Operate the vehicle within Failure Records

conditions as noted.

4. Using a Tech 2, monitor “ DTC” info for DTC P0113.

Does the Tech 2 indicate DTC P0113 failed?

—

Refer to

Test

Description

Refer to

Diagnostic

Aids

1. Ignition “OFF.”
2. Disconnect the IAT sensor electrical connector.
3. Jumper the IAT signal circuit and the sensor ground

circuit together at the IAT sensor harness
connector.

4. Ignition “ON.”
5. Observe the “Intake Air Temp” display on the Tech

Is the “Intake Air Temp” at the specified value?

140

(284

Go to

Step 6

Go to

Step 5

1. Jumper the IAT signal circuit at the IAT sensor

harness connector to chassis ground.

2. Observe the “Intake Air Temp” display on the Tech

Is the “Intake Air Temp” at the specified value?

140

(284

Go to

Step 7

Go to

Step 8

Check for poor connections at the IAT 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 IAT sensor

ground circuit for an open.

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

necessary.

Was the IAT sensor ground circuit open?

—

Verify repair

Go to

Step 9

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