P0118

P0118-ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT HIGH





For complete wiring diagrams refer to Diagrams/Electrical.


Theory of Operation

The coolant temperature sensor is a variable resistor sensor and is used to measure the temperature of the coolant of the engine. The ECM supplies 5-volts to the coolant temperature signal circuit. The ECM monitors the change in voltage caused by changes in the resistance of the sensor to determine the coolant temperature. The engine coolant temperature value is used by the ECM for the engine protection system and engine emissions control. The engine coolant temperature sensor is located near the thermostat housing. This fault is lit if the ECM detects that the coolant temperature signal voltage is less than a calibratable voltage for a calibratable amount of time. When the fault is active the customer may complain of white smoke and the fan will stay ON. There is NO engine protection for high engine coolant temperature if this fault is active. The ECM illuminates the MIL lamp after the diagnostic runs and fails once. The ETC lamp will also be illuminated. During this time a default value is used for the coolant temperature reading. The ECM will turn off the MIL lamp after the diagnostic runs and passes in 4 consecutive drive cycles.

- When Monitored:

With ignition on and battery voltage greater than 10.4 volts.

- Set Condition:

The circuit voltage to the ECM is above a calibrated threshold for a certain period of time.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test


1. COOLANT TEMPERATURE SENSOR

Disconnect the coolant temperature sensor harness connector.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance of the coolant temperature sensor.

Is the resistance between 300 and 90k ohms?

Yes

- Go To2

No

- Replace the coolant temperature sensor.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. INTERMITTENT CONDITION

Reconnect the disconnected coolant temp sensor harness connector.

With the scan tool, erase DTCs.

With the scan tool, read DTCs.

Did the DTC return?

Yes

- Go To3

No

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition

3. HIGH RESISTANCE IN CIRCUIT





Turn the ignition off.

Disconnect the ECM harness connector.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance between the (K2) temperature sensor signal and (K914) return circuit at the ECM harness connector with the coolant temp sensor harness connected.

Is the resistance between 300 and 90k ohms?

Yes

- Go To6

No

- Go To4

4. (K2) SIGNAL CIRCUIT OPEN





Disconnect the coolant temperature sensor harness connector.

Measure the resistance of the (K2) coolant temperature sensor signal circuit between the coolant temperature sensor connector and the ECM connector.

Is the resistance less than 10 Ohms?

Yes

- Go To5

No

- Repair or replace the open (K2) signal circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

5. (K914) SENSOR RETURN CIRCUIT OPEN





Measure the resistance of the (K914) coolant temperature sensor return circuit between the coolant temperature sensor connector and the ECM connector.

Is the resistance less than 10 Ohms?

Yes

- Go To6

No

- Repair or replace the open (K914) sensor return circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

6. (K2) SIGNAL CIRCUIT SHORTED





Measure the resistance of (K2) signal circuit to all other circuits at the ECM harness connector.

Is the resistance more than 100k ohms?

Yes

- Go To7

No

- Repair or replace the (K2) coolant temperature sensor signal circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

7. ECM





Reconnect the ECM harness connectors.

Turn the ignition on.

With the scan tool, erase DTCs.

While monitoring with scan tool, use a jumper wire and connect the sensor (K2) signal circuit to the (K914) sensor return circuit at the sensor connector.

Did the DTC P0117 set?

Yes

- Test Complete.

No

- Replace the ECM.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test