DTC P0087: Fuel Rail Pressure Low: Description
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The Engine Control Module (ECM) monitors Fuel Rail Pressure (FRP) using the FRP sensor. If the sensor indicates a pressure less than the commanded rail pressure plus a possible transitional overshoot, the ECM will set DTC P0087 for fuel rail pressure too low.