This part controls the output pressure of the high pressure CP3 fuel pump. When it fails, the actual fuel pressure will NOT match the desired or commanded fuel pressure as set by the engine computer. Actual and commanded pressure can be monitored on a scan tool and compared. The most common symptom of failure is varying / unstable idle. Compatibility 2003-2007 5.9L Dodge Ram Cummins Diesel Package content 1 x Fuel Regulator