Engine - Coolant Temperature Sensor/Switch: Description and Operation

Engine Coolant Temperature Sensor G62

The Engine Coolant Temperature (ECT) sensor is a variable resistance thermal switch. An isolated 5 volt output from the Engine Control Module (ECM) flows through the resistance of the ECT sensor to ground, changing the voltage of the circuit. The resistance of the sensor decreases as the temperature increases. The ECM reads this altered voltage of the 5 volt circuit to calculate the sensor temperature.

The ECT sensor is a primary input to the ECM for multiple tasks ranging from control of fuel trim, spark timing and secondary air operation, to multiple emission monitors which are dependant on engine temperature. It is also used as a comparison sensor to test for sensor accuracy between the intake air temperature sensor (G42) and ambient temperature sensor calibration checks.