What does it mean?
The transmission fluid pressure (TFP) sensor, or switch, is used to determine internal transmission pressure. This information is relayed to the transmission control module (TCM) where it is used to determine control of various outputs, such as the pressure control solenoids. The TFP directly affects transmission shift quality. Some transmissions will have multiple transmission fluid sensors. The TFP is a type of sensor called a transducer, which changes internal resistance relative to pressure.
The powertrain control module (PCM) sends a reference voltage (typically 5 volts) to the sensor. The sensor then changes its internal resistance in relation to line pressure and sends a return signal voltage to the PCM. The TFP is often located inside the transmission or the valve body, making it difficult to access. Code P0871 indicates the TCM has detected incorrect TFP circuit performance.
A typical transmission pressure sensor Code P0871 indicates the TCM has detected incorrect TFP circuit performance.