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

Coolant Temperature Sensor:

The coolant temperature sensor, located on the water outlet to the upper radiator hose, is an electrical thermistor with negative temperature coefficient properties. Negative temperature coefficient means that the change in resistance is inversely proportional to the change in temperature (as temperature increases, resistance decreases). The fuel control unit and ignition control unit share a single temperature sensor. Each ECU applies a regulated constant voltage to the sensor, and monitors the voltage in its circuit. As temperature increases, sensor resistance decreases, causing a decrease in the measured voltage of the circuit. By monitoring the circuit voltage, the control units can calculate the engine temperature, and adjust the air/fuel ratio and ignition timing to meet the specific demands of the engine, at that temperature.