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

This sensor, attached to the cylinder head near the upper radiator hose, is another thermistor that also receives a 5 volt reference signal from the ECU. The sensor internal resistance, which varies with coolant temperature, determines the sensor voltage signal sent back to the ECU. By comparing the sensor signal voltage to the reference voltage, the ECU can determine coolant temperature and change the fuel mixture and spark advance based on coolant temperature input information received.