Transmission Fluid Temperature Sensor

The automatic Transmission Fluid Temperature (TFT) sensor is a negative temperature coefficient thermistor that provides information to the Powertrain Control Module (PCM) regarding transmission fluid temperature. The TFT sensor 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 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 PCM 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. When the transmission fluid is cold, the sensor resistance is high and the PCM senses a high signal voltage. As the transmission fluid warms, the sensor resistance lowers and the PCM senses lower voltage. The PCM uses the TFT reading to control the Torque Converter Clutch (TCC), line pressure adjustments, and temperature compensated shifts. The TFT range is -40 to 305°F (-40 to 151°C).

The PCM measures this voltage as another input to help control line pressure, shift schedules and TCC apply. When the TFT reaches 284°F (140°C), the PCM enters hot mode. Above this temperature the PCM 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 PCM applies TCC at all times in Third and Fourth gears. Also, the PCM performs the 2-3 and the 3-4 shifts earlier to help reduce the generation of fluid heat.