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

Engine Coolant Temperature (ECT) Sensor:

The Engine Coolant Temperature (ECT) sensor is a thermistor - a resistor whose resistance changes as a function of temperature. The ECT sensor is mounted in the engine coolant stream. The ECT sensor has 2 internal sensors, one portion (a single wire) controls cooling fan operation and is NOT controlled or monitored by the PCM. The other portion (2 wires) is PCM monitored.

The PCM monitored portion of the ECT sensor is a 2-wire sensor with a reference voltage and a ground provided by the PCM. Low coolant temperature produces a high resistance and high temperatures result in a low resistance.

The PCM supplies a 5 volt signal to the coolant sensor through a resistor in the PCM and measures the signal voltage. The voltage will be high when the engine is cold and low when the engine is hot.




The ECT sensor provides engine coolant temperature information to the PCM for fuel enrichment, the ignition timing, the air management, the idle speed control, and Closed Loop fuel control.