DTC P0089: Fuel Rail Pressure Sensor Indicating Fuel Pressure Higher Than Desired: 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) uses commanded fuel pump flow to determine a desired Fuel Rail Pressure (FRP). The actual fuel pressure is monitored using the FRP sensor. If the FRP sensor indicates a pressure more than 20 MPa greater than desired, DTC P0089 will set.