Transmission Temperature Sensor/Switch: Description and Operation

PURPOSE
The Powertrain Control Mode (PCM) measures the voltage across the Transmission Fluid Temperature (TFT) sensor to determine the temperature of the transmission fluid. The PCM uses this information to determine whether a cold start shift schedule is necessary. The cold start shift schedule allows quicker shifts when the transmission fluid is cold.

CONSTRUCTION
The TFT sensor is a thermistor type device located on the transmission main control valve body.

Transmission Fluid Temperature (TFT) Schematic:

OPERATION
The PCM supplies a 5.0 volt reference voltage to the TFT sensor. The sensor resistance lowers as the fluid temperature increases. This resistance variation results in a change in the voltage drop across the TFT and a corresponding change in the signal sent to the PCM.

RELATED DIAGNOSTIC TROUBLE CODES

DTC 636 - TFT sensor output was beyond self-test range.

DTC 637 - TFT sensor output was greater than the self-test maximum of 4.8 volts.

DTC 638 - TFT sensor output was below the self-test minimum value of 0.57 volts.

DTC 657 - TFT sensor output indicates that a transmission over temperature condition occurred.