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

Coolant Temperature Sensor:

PCM Wiring:

PURPOSE
The sensor provides coolant temperature information to the PCM/ECM for fuel enrichment, ignition timing, EGR operation, canister purge control, air management, idle speed control, and closed loop fuel control. A failure in the coolant sensor circuit should set either a code E014 or code E015. An intermittent problem in the coolant sensor circuit can set a code E073. The coolant sensor is a thermistor (a resistor which varies its resistance value based on temperature) mounted in the engine coolant stream.

OPERATION
The coolant sensor is a two wire component which receives a reference voltage signal from the PCM/ECM. Low coolant temperature produces a high resistance, while a high temperature produces low resistance. The PCM/ECM supplies a voltage signal to the coolant sensor through a resistor in the PCM/ECM and measures the signal voltage output. The voltage will be high when the engine is cold, and the voltage will be low when the engine is hot.