Fuel Rail Pressure Sensor
WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The fuel rail pressure (FRP) sensor is a pressure transducer. The PCM supplies about 5 volts on the FRP sensor reference circuit. The PCM also supplies a signal and ground circuit to the FRP sensor. When fuel pressure is high the signal voltage is high. The FRP signal is used by the PCM for fuel trim adjustment.