A typical common rail (fuel rail) system is composed of the following 2 fuel pressure sections. A suction side between the fuel tank and the fuel supply pump and a high-pressure side between the fuel supply pump and the injectors. The fuel is drawn from the fuel tank and then pumped into the fuel rail by 2 plungers that are located inside the fuel supply pump. The fuel rail pressure is regulated through the ECM's control of the FRP regulator based on signals from the FRP sensor. If the fuel rail pressure becomes excessive, the fuel rail pressure limiter opens to release the excessive pressure and returns the fuel into the fuel tank.
The technician can perform the appropriate system diagnostic using the fuel system check. The fuel system check assumes that the following are met.