Circuit DescriptionThe coolant temperature sensor is a variable resistor sensor and is used to measure the temperature of the coolant of the engine. 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.

Component LocationThe engine coolant temperature sensor is located on the exhaust side of the engine near the thermostat housing.

Conditions for Running the DiagnosticsThis diagnostic runs continuously when the engine is running if the coolant temperature was less than 52?C [126?F] when the engine was started.

Conditions for Setting the Fault CodesThe ECM detects that coolant temperature did not reach 72?C [162?F] in a specified amount of time.

Action Taken When the Fault Code is ActiveThe ECM illuminates the amber CHECK ENGINE lamp and/or malfunction indicator lamp (MIL) after the diagnostic fails on two consecutive trips.

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 engine coolant temperature rises above 72?C [162?F] and the diagnostic runs and passes.The ECM will turn off the amber CHECK ENGINE lamp after the diagnostic runs and passes.For On-Board Diagnostics (OBD) engines, the ECM will turn off the MIL after three consecutive trips where the diagnostic runs and passes.The ?Reset All Faults? command in INSITE? electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop TalkPossible causes of this fault code include:

Low coolant level or air in the cooling systemMalfunctioning coolant temperature sensorMalfunctioning engine coolant thermostat.

Possible Cause:1) Thermostat2) ECM calibration