Coolant Temperature Sensor/Switch (For Computer): Description and Operation

PURPOSE
The Engine Coolant Temperature (ECT) Sensor monitors coolant temperature with a thermistor whose resistance varies according to engine temperature. The Engine Control Module (ECM) uses this signal to control open/closed loop operation of the fuel injection system, overdrive on electronic transaxles, electronic spark advance, idle speed control system and other functions.

OPERATION
The ECM sends out a reference voltage of approximately five (5) volts to the ECT sensor. As coolant temperature changes, the internal resistance of the sensor will change, causing a varying voltage drop across the sensor. The ECM reads the voltage drop across the sensor as engine coolant temperature.