(TP) Throttle Position sensor
The (TP) Throttle Position sensor is located on the throttle body of a fuel injected engine. This type of sensor is known as a potentiometer; a variable resister used to control voltage in a circuit. The TP sensor is used to detect engine load and WOT or wide open throttle. The A/C clutch is disengaged when a WOT signal is received from the TPI sensor.
One lead is connected directly to the computer’s 5 volt supply voltage. This voltage pin is connected to one end of the resistance strip inside of the TP sensor. The ground wire is connected to the other end of this internal resistance strip. The third wire is connected to a movable arm that swipes across this internal resistance strip, sending a varying voltage signal back to the PCM. This is called the signal circuit of the sensor, because it's the lead the sends the varying or "changing" voltage signal to the PCM indicating changes in throttle angle.
The TP sensor is attached to the throttle plate shaft and changes output voltage as the throttle plate opens and closes. The output voltage is low or around 0.45 volts when the throttle is closed and is high or 4.5 volts at WOT. The fuel injection and ignition timing are adjusted by the PCM as the throttle plate and TP sensor are moved. If the driver suddenly accelerates their vehicle, the PCM would receive this 4.5 volt signal and increase the fuel injection timing to compensate.