P0117

P0117-ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT LOW





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 falls below a calibrated threshold for a certain period of time.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test


1. COOLANT TEMPERATURE SENSOR

Turn the ignition off.

Disconnect the Coolant Temp sensor harness connector.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance of the Temp 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 coolant temp sensor connected.

Turn the ignition on.

With the scan tool, erase DTCs.

With the scan tool, read DTCs.

Did the DTC reset?

Yes

- Go To3

No

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition

3. (K2) SENSOR SIGNAL CIRCUIT SHORTED TO GROUND





Turn the ignition off.

Disconnect the ECM harness connector.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance between the engine ground and the (K2) temperature sensor signal circuit at the sensor harness connector.

Is the resistance more than 100 k ohms?

Yes

- Go To4

No

- Repair or replace the short harness.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

4. WIRING HARNESS SHORTED





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

Is the resistance more than 100k ohms?

Yes

- Go To5

No

- Repair or replace shorted wiring harness
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

5. ECM

Reconnect the ECM harness connectors.

Reconnect the ECT harness connector.

Turn the ignition on.

With the scan tool, erase DTCs.

While monitoring the scan tool, Disconnect the temperature sensor harness connector.

Did the DTC P0118 set?

Yes

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition

No

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