Inside the water temperature sensor is a semiconductor thermistor, the lower the temperature, the greater the resistance; On the contrary, the smaller the resistance, installed in the engine cylinder block or cylinder head of the water jacket, direct contact with the cooling water. The temperature of engine cooling water is measured. According to this change, ECU measures the temperature of engine cooling water, the lower the temperature, the greater the resistance; Conversely, the smaller the resistance. The ECU uses this change to measure the temperature of the engine's cooling water as a correction signal for fuel injection and ignition timing. That is, we can know the running state of the car, stop or move, or how long the movement time, etc., by the temperature of the engine water temperature.