Circuit DescriptionThe coolant temperature sensor is a variable resistor sensor and is used to measure the temperature of the engine coolant. The engine control module (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. This fault code indicates that the engine coolant temperature has exceeded the engine protection limit.

Component LocationThe engine coolant temperature sensor is located on the thermostat housing.

Conditions for Running the DiagnosticsThis diagnostic runs continuously when the keyswitch is in the ON position or when the engine is operating.

Conditions for Setting the Fault CodesThe ECM detects that the coolant temperature is greater than 108? C [226?F] for more than 5 seconds.

Action Taken When the Fault Code is ActiveThe ECM illuminates the amber CHECK ENGINE lamp immediately when the diagnostic runs and fails.The torque output of the engine will be reduced.Exhaust gas recirculation (EGR) valve operation will be disabled.Conditions for Clearing the Fault CodeTo validate the repair using a Diagnostic Road Test, utilize a route that incorporates both stop-and-go city driving and steady state highway driving. It may be necessary to load the unit for certain diagnostics in the ECM to run.To validate the repair using a Chassis Dynamometer Test, utilize a routine that incorporates acceleration and motoring events, steady state highway operation, and load. This will simulate normal driving and allow the diagnostics in the ECM to run.The fault code status displayed by INSITE? electronic service tool will change to INACTIVE immediately after the coolant temperature decreases below the engine protection limit and the diagnostic runs and passes.The ECM will turn off the amber CHECK ENGINE lamp after the diagnostic runs and passes.The ?Reset All Faults? command in INSITE? electronic service tool can be used to clear active and inactive faults.

Shop TalkThis fault code indicates that coolant temperature has exceeded the engine protection limit for high coolant temperature. Refer to Engine Coolant Temperature Above Normal symptom troubleshooting tree in Section TS.

Possible Cause:1) Coolant Temperature Sensor failure2) ECM calibration