The coolant temperature sensor is installed on the engine block or cylinder head, and is in contact with the coolant to detect the temperature of the engine's circulating coolant; it is made of a negative temperature coefficient resistance resistor that is very sensitive to temperature changes, which varies according to the resistance change The signal voltage is input to the ECU as a correction signal for engine fuel injection and ignition. It is also used to control coolant fans, air conditioners, etc. Its role cannot be underestimated.