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

Figure 3-11: Coolant Temperature Sensor Circuit:

Engine Coolant Temperature Sensor Test

The coolant temperature sensor is a thermistor that provides a temperature signal to the PCM (Figure 3-11). The signal is in the form of a voltage that changes according to sensor resistance. At low temperatures, resistance and voltage are both high. As temperature increases, resistance and voltage both decrease.

A sensor fault will cause the check engine light to illuminate and the torque converter clutch to apply early. If the sensor fails in a cold mode, it can produce overrich operation and rough idle.