The TPF (Transmission Fluid Pressure) sensor determines the internal pressure of the transmission. Besides, it turns the mechanical pressure of the transmission into an electrical signal, which is sent to the Transmission Control Module (TCM). This data is used to control the outputs of the pressure solenoids. The quality of the transmission shift is highly dependent on the signal from the TPF Sensor. Some transmissions may have multiple TPF Sensors depending on the manufacturer.
The Powertrain Control Module (PCM) delivers 5 volts of the reference voltage to the TPF Sensor, and the TPF Sensor changes its internal resistance based on line pressure, then sends a signal voltage back to the PCM. The DTC P0846 OBDII is set when the PCM detects a malfunction in the TPF Sensor circuit.