As inputted rail pressure sensor signal, ECM of Commom rail diesel engine controls Fuel pressure regulator valve(intergrated with high press. pump) in order to maintain optimum rail pressure according to current engine rpm and load.

However when the problem that leads rail pressure to out of target value intended by ECM occurs due to mechanical or electronical reason, ECM shuts engine down and sets DTC by limiting fuel (stops injector operation) in order to prevent engine from being controlled abnormally. "rail pressure monitoring error" is the DTC which diagnose 1).supplying state of low pressure fuel and 2).mechanical operating conditions of high pressure pump and 3) indirectly based on RPS output voltage and RPS duty. thus, repair relavant to this DTC requires mechanics the total understand of fuel system.

In U-2 Engine, Rail Pressure Regulator Valve That located on the Commom Railis is deleted.