Automatic Transmission Fluid Temperature Sensor

The automatic Transmission Fluid Temperature (TFT) sensor controls TCC and line pressure. The TFT sensor attaches to the upper control valve assembly. The TFT signals the PCM regarding transmission fluid temperature. The sensor is a negative temperature coefficient thermistor which receives a 5-volt reference signal from the PCM. When the temperature is cold, the sensor resistance is high; therefore, the PCM sees a high signal voltage. As the fluid warms, the sensor resistance decreases, the voltage drop across the sensor becomes lower.

A PCM internal shunt circuit comes into play as the temperature increases beyond 122°F (50°C). As the temperature decreases, the internal shunt comes out at 104°F (40°C). There is a 18°F (10°C) overlap. TFT operating range is -40 to 305°F (-40 to 151°C). The TFT sensor may be tested with an ohmmeter across pin terminals "L" and "M" of the 20-way transmission harness connector. See appropriate article in TRANSMISSIONS.