Theory Of Operation

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The tests used to diagnose the closed loop fuel rail pressure control system for pressure that is inappropriately high or inappropriately low.

The fuel rail pressure (FRP) sensor is used to measure the fuel pressure in the diesel common rail system. The FRP sensor is the feedback component in a control loop, and informs the Powertrain Control Module (PCM) about the current pressure in the common rail. The PCM controls the desired rail pressure by operating two valves - called fuel metering valve and a pressure control valve. The correctness of the FRP sensor is important since the inaccuracy can lead to an emission disadvantage. Generally, a reduced rail pressure can lead to an increase in soot emissions while reducing engine out NOx emissions.