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

The engine coolant temperature sensor is a thermistor, installed where it protrudes into the engine coolant flow. When the coolant temperature is low, the sensor produces a high resistance. When the coolant temperature is high, the sensor produces a low resistance.

The ECM sends a 5 volt signal to the coolant temperature sensor through a resistor in the ECM and measures the voltage. A high voltage will be indicated when the coolant temperature is low, and low when the coolant temperature is high.

The ECM uses this information to control systems where operation is temperature dependant.