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

Coolant Temperature Sensor:

The coolant sensor is a thermistor (a resistor which varies resistance depending on temperature) mounted in the engine coolant stream. When temperature is low, resistance is high. Resistance decreases as temperature increases.

The ECM supplies a reference voltage to the coolant sensor through a resistor in the ECM, and monitors the voltage in the circuit. The voltage will be high when the engine is cold. As temperature increases, sensor resistance drops and voltage in the circuit drops proportionally.

The sensor provides coolant temperature information to the 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 E14 or code E15.