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Isuzu KB P190. Manual - part 838

Engine Management – V6 – Diagnostics

Page 6C1-2–74

Step Action

Yes

Switch off the ignition for 30 seconds.

Start the engine.

Allow the engine to reach the normal operating temperature.

Using Tech 2, select the DTC display function.

Does DTC P0112 or P0113 fail this ignition cycle?

Go to Step 3

Refer to Additional

Information in this

DTC

Switch off the ignition.

Disconnect the IAT sensor wiring connector.

Switch on the ignition with the engine not running.

Using a digital multimeter, measure the voltage between the IAT
sensor signal circuit and the ECM housing.

Does the multimeter display 4.8 – 5.2 V?

Go to Step 4

Go to Step 5

Switch off the ignition.

Remove ECM Fuse 29 from the engine compartment fuse and
relay panel assembly.

Using a digital multimeter, measure the resistance between the
IAT sensor low reference circuit and the ECM housing.

N O T E

Install the ECM Fuse 29 to the engine compartment fuse
and relay panel assembly after completing this test.

Does the multimeter display 5

Ω?

Go to Step 7

Go to Step 6

Test the IAT sensor signal circuit for a high resistance, open circuit,
short to ground or short to voltage fault condition. Refer to 8A
Electrical - Body and Chassis for information on electrical fault
diagnosis.

Was any fault found and rectified?

Go to Step 9

Go to Step 8

Test the IAT sensor low reference circuit for a high resistance, open
circuit, short to ground or short to voltage fault condition. Refer to 8A
Electrical - Body and Chassis for information on electrical fault
diagnosis.

N O T E

The IAT sensor shares the low reference circuit with other
sensors. A fault condition in the low reference circuit may
trigger DTCs on sensors that share this circuit. Refer to
3 Wiring Diagrams and Connector Charts in this Section,
to assist diagnosis.

Was any fault found and rectified?

Go to Step 9

Go to Step 8

Replace the IAT sensor. Refer to 6C1-3 Engine Management – V6 –
Service Operations

Was the repair completed?

Go to Step 9

—

Replace the ECM. Refer to 6C1-3 Engine Management – V6 –
Service Operations

Was the repair completed?

Go to Step 9

—

Engine Management – V6 – Diagnostics

Page 6C1-2–75

Step Action

Yes

Using Tech 2, clear the DTCs.

Switch off the ignition for 30 seconds.

Start the engine.

Operate the vehicle within the conditions for running the DTC.

Does any of the IAT sensor DTCs fail this ignition cycle?

Go to Step 2

Go to Step 10

10 Using Tech 2, select the DTC display function.

Does Tech 2 display any DTCs?

Go to the

appropriate DTC

Table in this Section

System OK

When all diagnosis and repairs are completed, check the system for correct operation.

7.8

DTC P0116, P0117, P0118, P0125 or
P1258

DTC Descriptors

This diagnostic procedure supports the following DTCs:

•

DTC P0116 – Engine Coolant Temperature Sensor Circuit Range / Performance

•

DTC P0117 – Engine Coolant Temperature Sensor Circuit Low Voltage

•

DTC P0118 – Engine Coolant Temperature Sensor Circuit High Voltage

•

DTC P0125 – Insufficient Engine Coolant Temperature For Closed Loop Fuel Control

•

DTC P1258 – Engine Coolant Over Temperature - Protection Mode Active

Circuit Description

The ECM applies a reference 5 V to the engine coolant temperature (ECT) sensor signal circuit and ground through the
low reference circuit. The ECT sensor is a variable resistor that measures the temperature of the engine coolant.

•

Increased temperature in the engine coolant decreases the resistance value of the ECT sensor. This increases the
ECT sensor pull-down rate to ground. Therefore, the higher the engine coolant, the lower the signal voltage output
of the ECT sensor.

•

Decreased temperature in the engine coolant increases the resistance value of the ECT sensor. This reduces the
ECT sensor pull-down rate to ground. Therefore, the lower the engine coolant temperature, the higher the signal
voltage output of the ECT sensor.

An ECT sensor DTC sets if the ECM detects the engine coolant temperature is outside the predetermined range.

Conditions for Running the DTC

DTC P0116

Runs continuously when the engine is running.

DTC P0117, P0118 and P1258

Runs continuously when the ignition is switched on.

DTC P00125

Runs continuously once the following conditions are met:

•

DTCs P0112, P0113, P0117 or P0118 are not set.

•

The engine is running.

Engine Management – V6 – Diagnostics

Page 6C1-2–76

Conditions for Setting the DTC

DTC P0116

The ECM detects the engine coolant temperature sensor value is 10°C less than the minimum calculated engine
temperature.

DTC P0117

The ECM detects the engine coolant temperature is greater than 140

°C for longer than 3 seconds.

DTC P0118

The ECM detects the engine coolant temperature is less than -39

°C for longer than 3 seconds.

DTC P0125

The ECM determines the calculated engine temperature by measuring the amount of airflow into the engine. This DTC
sets if the ECM detects the actual ECT sensor is not within 10ºC of the calculated engine temperature for approximately
2 – 5 minutes.

DTC P1258

The ECM detects the engine coolant temperature is greater than 131

°C for longer than 2 seconds.

Conditions for Clearing the DTC

The ECT sensor DTCs are Type B DTCs. Refer to 1.4 Diagnostic Trouble Codes in this Section, for action taken when a
Type B DTC sets and conditions for clearing Type B DTC.

Additional Information

•

Refer to 6C1-1 Engine Management – V6 – General Information for details of the ECT sensor operation.

•

For an intermittent fault condition, refer to 5.2

Intermittent Fault Conditions in this Section.

•

DTCs P0116, P0117, P0118 and P0125 diagnostic table is developed with the assumption the engine cooling
system is functioning correctly. Therefore, rectify any engine cooling system fault conditions before proceeding
with this diagnostic table.

•

Test the ECT sensor using the ECT Temperature vs. Resistance in 6C1-3 Engine Management –V6 – Service
Operations. If the engine has sat overnight, the ECT sensor should display within 3

°C of the IAT sensor values.

When the engine is first started, the ECT should rise steadily to about 90

°C then stabilise when thermostat opens.

•

Since fault condition in a wiring connector may trigger DTCs, always test the connectors related to this diagnostic
procedure for shorted terminals or poor wiring connection before replacing any component. Refer to 8A Electrical -
Body and Chassis for information on electrical fault diagnosis.

•

To assist diagnosis, refer to 3 Wiring Diagrams and Connector Charts in this Section, for the system wiring
diagram and connector charts.

Test Description

The following numbers refer to the step numbers in the diagnostic table:

A fault condition in the engine cooling system may trigger these DTCs.

The ECT sensor low reference circuit is shared with other components. DTC P0118 may set if the shared low
reference circuit is shorted to voltage. Test the low reference circuit of all components that share this circuit to find
the source of the fault condition.

DTC P0116, P0117, P0118, P0125 and P1258 Diagnostic Table

Step Action

Yes

Has the Diagnostic System Check been performed?

Go to Step 2

Refer to

4.4 Diagnostic

System Check in

this Section

Engine Management – V6 – Diagnostics

Page 6C1-2–77

Step Action

Yes

Test the engine cooling system for correct operation. Refer to 6B1
Engine Cooling – V6.

Was any fault found and rectified?

Go to Step 10

Go to Step 3

Switch off the ignition for 30 seconds.

Operate the vehicle within the conditions for running the DTC.

Using Tech 2, select the DTC display function.

Does DTC P0116, P0117, P0118, P0125 or P1258 fail this ignition
cycle?

Go to Step 4

Refer to Additional

Information in this

DTC

Switch off the ignition.

Disconnect the ECT sensor wiring connector.

Switch on the ignition with the engine not running.

Using a digital multimeter, measure the voltage between the
ECT sensor signal circuit and the ECM housing.

Does the multimeter display 4.8 – 5.2 V?

Go to Step 5

Go to Step 6

Switch off the ignition.

Remove ECM Fuse 29 from the engine compartment fuse and
relay panel assembly.

Using a digital multimeter, measure the resistance between the
ECT sensor low reference circuit and the ECM housing.

N O T E

Install the ECM Fuse 29 to the engine compartment fuse
and relay panel assembly after completing this test.

Does the multimeter display 5

Ω?

Go to Step 8

Go to Step 7

Was any fault found and rectified?

Go to Step 10

Go to Step 9

Test the ECT sensor low reference circuit for a high resistance, open
circuit, short to ground or short to voltage fault condition. Refer to 8A
Electrical - Body and Chassis for information on electrical fault
diagnosis.

N O T E

The ECT sensor shares the low reference circuit with other
sensors. A fault condition in the low reference circuit may
trigger DTCs on sensors that share this circuit. Refer to 3

Wiring Diagrams and Connector Charts in this

Section, to assist diagnosis.

Was any fault found and rectified?

Go to Step 10

Go to Step 9

Replace the ECT sensor. Refer to 6C1-3 Engine Management – V6 –
Service Operations.

Was the repair completed?

Go to Step 10

—

Replace the ECM. Refer to 6C1-3 Engine Management – V6 –
Service Operations.

Was the repair completed?

Go to Step 10

—

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