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

DESCRIPTION
The ECT sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant flow.

OPERATION
At cold coolant temperatures, the ECT sensor resistance is high and at hot coolant temperatures, the resistance of the sensor is low. The PCM supplies a 5 volt reference signal and a ground to the sensor and measures the voltage signal as it is changed by the sensor. The voltage is close to 5 volts at cold temperatures and close to zero volts at hot temperatures.

The PCM uses ECT information for fuel enrichment, ignition control, canister purge control, idle speed control and Closed Loop fuel control. A faulty ECT sensor may cause various driveability conditions and should set a Diagnostic Trouble Code.