Isuzu Trooper (1998-2002 year). Manual - part 493

6E–342

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC)

P1112 IAT Sensor Circuit Intermittent Low Voltage

D06RY00168

Circuit Description

The intake air temperature (IAT) sensor is a thermistor
which measures the temperature of the air entering the
engine. The powertrain control module (PCM) 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
PCM will monitor a high signal voltage on the IAT signal
circuit. If the intake air is warm, the sensor resistance
becomes lower, causing the PCM to monitor a lower
voltage. DTC P1112 will set when the PCM intermittently
detects an excessively low signal voltage on the intake air
temperature sensor signal circuit.

Conditions for Setting the DTC

The engine has been running for over 15 seconds.

Vehicle speed is greater than 48 km/h (30 mph).

IAT signal voltage is greater than 148

C (298

(about 0.10 volt) for a total of 2.5 seconds over a
25-second period of time.

Action Taken When the DTC Sets

The PCM will not illuminate the malfunction indicator
lamp (MIL).

The PCM will store conditions which were present
when the DTC was set as Failure Records data only.
This information will not be stored as Freeze Frame
data.

The PCM will substitute a default value for intake air
temperature.

Conditions for Clearing the MIL/DTC

A history DTC P1112 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

DTC P1112 can be cleared by using the Tech 2 “Clear
Info” 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
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.

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.

6E–343

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

2. Verifies that the fault is present.

3. If DTC P1112 can be repeated only by duplicating

the Failure Records conditions, refer to the
“Temperature vs. Resistance Value Chart”. The
chart may be used to test the IAT 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 IAT sensor.

Intake Air Temperature Sensor

OHMS

Temperature vs. Resistance Values

(approximate)

100

212

177

176

332

140

667

113

1188

1802

2796

4450

7280

–5

12300

–15

21450

–30

–22

52700

–40

100700

DTC P1112 – IAT Sensor Circuit Intermittent 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

Is DTC P0112 also set?

—

Go to

DTC

P0112 first

Go to

Step 3

1. Check the IAT signal circuit between the IAT sensor

connector and the PCM for an intermittent short to
ground.

2. If a problem is found, repair as necessary.

Was a problem found?

—

Verify repair

Check the

Procedure

Refer to

Diagnostic

Aids

6E–344

6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC)

P1114 ECT Sensor Circuit Intermittent Low Voltage

D06R200049

Circuit Description

The engine coolant temperature (ECT) sensor is a
thermistor mounted in the engine coolant stream. The
powertrain control module (PCM) applies a voltage
(about 5.0 volts) through a pull-up resistor to the ECT
signal circuit. When the engine coolant is cold, the sensor
(thermistor) resistance is high, therefore the PCM will
measure a high signal voltage. As the engine coolant
warms, the sensor resistance becomes less, and the
ECT signal voltage measured at the PCM drops. With a
fully warmed up engine, the ECT signal voltage should
measure about 1.5 to 2.0 volts. If the PCM detects an
ECT signal that is intermittently below the range of the
ECT sensor, DTC P1114 will set.

Conditions for Setting the DTC

Engine run time longer than 120 seconds.

The ECT sensor signal is intermittently greater than
150

C (302

F) (about 0.10 volt) for a total of 10

seconds over a 100-second period.

Action Taken When the DTC Sets

The PCM will not illuminate the malfunction indicator
lamp (MIL).

The PCM will store conditions which were present
when the DTC set as Failure Records data only. This
information will not be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC

A history DTC P1114 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

DTC P1114 can be cleared by using the Tech 2 “Clear
Info” 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
ECT display on the Tech 2 while moving connectors
and wiring harnesses related to the ECT sensor. A
change in the ECT 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

6E–345

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

the condition that caused the DTC to be set occurs. This
may assist in diagnosing the condition.

Engine Coolant Temperature Sensor

OHMS

Temperature vs. Resistance Values

(approximate)

100

212

177

176

332

140

667

113

1188

1802

2796

4450

7280

–5

12300

–15

21450

–30

–22

52700

–40

100700

DTC P1114 – ECT Circuit Intermittent 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

Is DTC P0117 also set?

—

Go to

DTC

P0117 first

Go to

Step 3

1. Check the ECT signal circuit between the ECT

sensor connector and the PCM for an intermittent
short to ground.

2. If a problem is found, repair as necessary.

Was a problem found?

—

Verify repair

Check the

Procedure

Refer to

Diagnostic

Aids

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