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

Coolant Temperature Sensor:

ECM Wiring:

PURPOSE
The Engine Coolant Temperature (ECT) sensor provides coolant temperature information to the Engine Control Module (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 Diagnostic Trouble Code (DTC) 14 or DTC 15. 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 ECM. Low coolant temperature produces a high resistance, while a high temperature produces low resistance. The ECM supplies a voltage signal to the coolant sensor through a resistor in the 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.