Automatic Transmission Fluid Temperature Sensor
The automatic transmission fluid temperature (TFT) sensor is a negative temperature coefficient thermistor (temperature sensitive resistor) that provides information to the control module regarding the transmission fluid temperature. The TFT sensor clips on to the valve body and is replaced as a separate component and not as a part of the AT wiring harness assembly. The TFT sensor monitors non-pressurized fluid in the sump in order to determine the operating temperature of the transmission fluid.
The internal electrical resistance of the sensor varies in relation to the operating temperature of the transmission fluid. The control module sends a 5 volt reference signal to the TFT sensor and the control module measures the voltage drop in the electrical circuit. A lower fluid temperature creates a higher resistance in the TFT sensor, which produces a higher voltage signal.
The control module uses this input in order to help determine the proper line pressure, shift schedules and TCC apply. When the transmission fluid temperature reaches 130°C (266°F), the control module enters Hot Mode. Above this temperature the control module modifies the transmission shift schedules and the TCC apply in an attempt to reduce the fluid temperature by reducing the transmission heat generation. During Hot Mode the control module applies the TCC at all times in third and fourth gears. Also, the control module performs the 2-3 and the 3-4 shifts earlier in order to help reduce fluid heat generation.
The control module stays in Hot Mode until the temperature drops below 120°C (248°F).