The automatic transmission oil temperature sensor is installed on the control valve and is used to detect the temperature of the hydraulic oil of the automatic transmission, which is used as the basis for the computer to perform shift control, oil pressure control and lockup clutch control. The internal of the hydraulic oil temperature sensor is a semiconductor thermistor, which has a negative temperature resistance coefficient. The higher the temperature, the lower the resistance. The computer measures the temperature of the hydraulic oil of the automatic transmission according to the change in its resistance. When the transmission oil temperature is higher than 150℃, the torque converter immediately enters the lock-up mode.