With Vehicle Control Module (VCM-A)

The Engine Coolant Temperature (ECT) sensor, is a thermistor (a resistor which changes value based on temperature) immersed in the engine coolant stream. Low coolant temperature produces a high resistance, while high temperature causes low resistance.

The Vehicle Control Module (VCM-A) supplies a 5 volt signal to the ECT through a resistor in the VCM-A and measures the voltage across the ECT. The voltage will be high when the engine is cold, and low when the engine is hot. By measuring the voltage, the VCM-A knows the engine coolant temperature. Engine coolant temperature affects most systems the VCM-A controls.

Diagnostic Trouble Code (DTC) PO118 or DTC PO117 indicates a failure in the engine coolant temperature sensor circuit.

Most scan tools display engine coolant temperature in degrees centigrade. After engine is started the temperature should rise steadily to about 90°C (194° F), then stabilize when thermostat opens.