Circuit/System Description
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The engine control module (ECM) uses the fuel rail pressure (FRP) sensor to monitor the high side fuel pressure and the fuel rail pressure relief valve performance. The fuel rail pressure relief valve is designed to release fuel pressure in the event of an overpressure condition. This diagnostic looks for excessive fuel rail pressure decay to detect an open fuel rail pressure relief valve.