Transmission Fluid Temperature Sensor

The Transmission Fluid Temperature (TFT) sensor contains a semiconductor device which changes resistance based on temperature (a thermistor). The TFT sensor is located inside the transmission in the main case wiring harness. The TFT sensor has a signal circuit and a ground circuit. The TCM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The TCM monitors changes in this signal voltage. The TCM interprets the resulting change in the resistance of the sensor and determines the transmission fluid temperature.

When the fluid is cold, the sensor (thermistor) resistance is high, and the TCM's signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the TCM will sense a high signal voltage (low temperature). When the fluid is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the TCM to sense a low signal voltage (high temperature).