Transmission Temperature Sensor/Switch: Description and Operation

TRANSMISSION FLUID TEMPERATURE (TFT) SENSOR





The Transmission Fluid Temperature (TFT) sensor is a negative temperature coefficient thermistor (temperature sensitive resistor) that provides information to the Powertrain Control Module (PCM) regarding transmission fluid temperature. The temperature sensor is integrated in the Automatic Transmission Fluid Pressure Manual Valve Position Switch Assembly (TFP val. position sw.) which is bolted to the valve body. The sensor monitors pressurized main line pressure from the inside of the valve body to determine the operating temperature of the transaxle fluid. The sensor, similar to each of the TFP val. position sw., uses an O-ring seal to maintain fluid pressure in the valve body.
The internal electrical resistance of the sensor varies in relation to the operating temperature of the transmission fluid (see chart).








The PCM sends a 5 volt reference signal to the temperature sensor and measures the voltage drop in the electrical circuit. A lower fluid temperature creates a higher resistance in the temperature sensor, thereby measuring a higher voltage signal.
The PCM measures this voltage as another input to help control line pressure, shift schedules and Torque Converter Clutch (TCC) apply. When transaxle fluid temperature reaches 140°C (284°F) the PCM enters "hot mode." Above this temperature the PCM modifies transmission shift schedules and TCC apply in an attempt to reduce fluid temperature by reducing transmission heat generation. During hot mode the PCM applies the TCC at all times in third and fourth gears. Also, the PCM performs the 2-3 and 3-4 shifts earlier to help reduce fluid heat generation. Hot mode may not be available on some applications.