The Transmission Fluid Temperature (TFT) sensor produces an electrical signal that it sends to the Powertrain Control Module (PCM) to determine shift points, Torque Converter Clutch (TCC) control and line pressure. This sensor is usually found in the transmission oil pan.
The TFT sensor receives 5 volts of reference voltage from the PCM. It should be noted that the internal resistance of this sensor varies with transmission fluid temperature, and this is returned as a signal to the PCM.
If the DTC P0712 OBDII code is set, it is because the PCM has discovered a low signal on the TFT sensor and the Check Engine light will illuminate. This is usually due to a short in the circuit.