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

Engine Coolant Temperature (ECT) Sensor:

The ECT sensor is located in a coolant passage in the side of the cylinder head near the thermostat housing. The ECT sensor is a two-wire thermistor type sensor that varies resistance according to changes in engine coolant temperature. The ECM supplies a five volt reference through a resistor to the sensor, which is connected to ground. When the sensor is cold it has high resistance (high signal voltage at ECM). As the sensor temperature increases, its resistance decreases (lower signal voltage at ECM). The ECM uses the signal voltage to determine engine coolant temperature.

Temperature Vs Resistance:

The ECT sensor is used by the ECM for fuel control (calculation of temperature of air/fuel mixture at the intake valve in conjunction with the IAT sensor temperature), Coolant Temperature telltale illumination, coolant temperature gauge position and cooling fan operation. The ECM also uses the ECT sensor for ignition timing, EVAP purge solenoid control, idle speed control and oil life monitoring.