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

Coolant Temperature Sensor (CTS):

The Engine Coolant Temperature Sensor (ECT) is a thermistor (a resistor whose resistance changes as a function of temperature) and is mounted in the coolant stream. The ECT is a two wire sensor with a referance 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 five-volt signal to the 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 coolant temperature information to the PCM for fuel enrichment, ignition timing, air management , idle speed control and closed loop fuel control.

A failure in the ECT sensor circuit should set a Diagnostic Trouble Code (DTC) 22.