Fuel Rail Pressure Sensor
WARNING: This page is about a different car, the 2013 Infiniti M56. However, it is still accessible from the selected car via links, so may be relevant.
The fuel rail pressure (FRP) sensor is placed to the fuel rail and measures fuel pressure in the fuel rail. The sensor transmits voltage signal to the ECM. As the pressure increases, the voltage rises. The ECM controls the fuel pressure in the fuel rail by operating high pressure fuel pump. The ECM uses the signal from fuel rail pressure sensor as a feedback signal.