Transmission Fluid Temperature (TFT) Sensor

Fluid Pressure Switch Assembly:

Electronic Component Location Views:

PURPOSE
The PCM uses the transmission fluid temperature sensor to regulate [1][2]torque converter clutch apply, and shift quality.

OPERATION
The transmission fluid temperature sensor is a thermistor (a resistor that changes value based temperature) mounted in the fluid pressure switch assembly. Low transmission fluid temperature produces high resistance while high transmission fluid temperature produces low resistance. The PCM supplies a 5 volt signal to the transmission fluid temperature sensor through an internal resistor then measures the voltage drop in the circuit. Voltage will be high when the transm~ssion is cold and low when the transmission is hot.
DTC 58 and 59 indicate a fault in the circuit. Most scan tools will display transmission fluid temperature in degrees Celsius. After the vehicle has been started, transmission temperature should rise steadily and stabilize between 90 and 115 degrees Celsius depending on the load. Both DTC(s) will cause the PCM to act as if the transmission were warm in either case. The scan tool will display -40°C for an open circuit or 154°C for a grounded circuit. When DTC 58 or 59 are set the [1][2]torque converter clutch is enabled in second, third, fourth, and will apply early. Some driveability symptoms will be noticed, especially when cold.


DTC 79 indicates a fault in the transmission fluid temperature.

HOT MODE
The scan tool will display this value either "ON" or "OFF." When displayed "ON," the transmission fluid temperature has become greater than 135°C and the following actions will occur:

1. The TCC will engage in fourth gear, except when the brakes are applied, low TP signal, or a DTC is stored.

2. When the fluid temperature obtains 150°C but, less than 154°C for 15 minutes, DTC 79 will set. When DTC 79 is set, TCC application will still occur in the same criteria as when hot mode started

3. When fluid temperature increases from 150°C, to greater than 154°C for 1 second, in a time period less than 15 minutes, DTC 79 will not set. DTC 58 will set when transmission fluid temperature sensed is greater than 154°C for 1 second.

4. When DTC 58 is set and in hot mode, the vehicle will retain hot mode criteria until the next ignition cycle

5. If fluid temperature cools from 135°C down to less than 125°C, hot mode criteria will discontinue.