This bulletin addresses concerns for rough running, surging and misfires on 2004-2005 GMC Silverado, Sierra, Kodiak and Topkick vehicles equipped with a 6.6L engine.

Do not replace fuel injectors for DTCs P1223, P1226, P1229, P1232, P1235, P1238, P1241 or P1244. When these codes are set, there is either a wiring concern between the ECM and the fuel injection control module (FICM), or a concern with the ECM and/or FICM. If there is a concern on the injector drive circuits (open, short to ground or high resistance), it is possible to have a high injector balance rate.

1. Diagnose all injector drive codes using the current Sl diagnostics.

2. If all Sl diagnostics are inconclusive, inspect for wire chafes at the FICM wiring harness brace. This brace is located 4-6 inches from the FICM connectors. The wiring harness is nylon tied to the harness brace. Remove the nylon tie to inspect the harness. Repair any damage found, and insulate the harness so that chafing will not occur again.

3. Also inspect the C107 (Silverado and Sierra) or C118 (Kodiak and Topkick) connector for wire chafes. This connector is found above the left rocker cover.

4. Use GMVIS to check the build date of the vehicle. If the vehicle is a 2005 light duty C/K truck, built between 3-3-2005 and 3-15-2005, refer to Inventory Upgrade Bulletin number 05054. This describes a possible coolant leak from the coolant surge tank, which might wick into the engine wiring harness and induce injector drive codes.

Carefully inspect for wire chafing along the FICM harness.

Carefully inspect for wire chafing along the FICM harness.