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

Engine Coolant Temperature Sensor:

PURPOSE
The coolant sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. This changing resistance supplies the Electronic Control Module (ECM) with the engine coolant temperature.

OPERATION
The ECM supplies a 5 volt signal to the coolant sensor through a resistor in the ECM and measures the voltage. The voltage will be high when the engine is cold and low when the engine is hot. By measuring the voltage, the ECM knows the engine coolant temperature. Engine coolant temperature affects most systems the ECM controls.

A failure in the coolant sensor circuit should set either a Code 14 or Code 15. Remember, these codes indicate a failure in the coolant temperature circuit, so proper use of the chart will lead to either repairing a wiring problem or replacing the sensor to properly repair a problem. Once the trouble code is set, the ECM will use a default valve for engine coolant temperature.