CODE 51,55;FUEL FLOW INTERRUPT POSSIBLE MISSING CALPAK

When Codes 51 or 55 are indicated and fuel delivery to the engine is interrupted, the ECM should be checked for a missing Calpac. Code 52 will NOT register if the Calpac is missing. If the Calpac is in place, normal diagnostics should be used to check for a malfunctioning PROM or ECM.

When servicing the ECM, both the Calpac and PROM must be transferred to the new ECM.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.