Automatic Transmission Fluid Temperature Sensor
The automatic transmission fluid temperature (TFT) sensor is a negative temperature coefficient thermistor that provides information to the TCM regarding transmission fluid temperature. The TFT sensor (1) is integrated in the automatic transmission fluid pressure (TFP) manual valve position switch assembly which is bolted to the control valve body. The sensor monitors main line pressure from the inside of the control valve body in order to determine the operating temperature of the transmission fluid. The sensor uses an O-ring seal to maintain fluid pressure in the control valve body.
The internal electrical resistance of the sensor varies in relation to the operating temperature of the transmission fluid. The TCM sends a 5 volt reference signal to the sensor. This measures the voltage drop in the electrical circuit. A lower fluid temperature creates a higher resistance in the TFT sensor, thereby measuring a higher voltage signal.
The TCM measures this voltage as another input to help control line pressure, shift schedules and TCC apply. When the TFT reaches 140°C (284°F), the TCM enters hot mode. Above this temperature the TCM modifies the transmission shift schedules and TCC apply in an attempt to reduce fluid temperature by reducing the amount of heat generated by the transmission. During hot mode the TCM applies TCC at all times in Third and Fourth gears. Also, the TCM performs the 2-3 and the 3-4 shifts earlier in order to help reduce the generation of fluid heat. Refer to Transmission Fluid Temperature Sensor Specifications .