Intermittent Service 4WD Light Comes On With DTC C0306 Or C0308 Stored In TCCM - keywords 1625 1626 246 263 246EAU 263EAU 3023 case MIL NP1 NP8 NQF NQH transfer
| Subject: | Intermittent Service 4WD Light Comes On With DTC C0306 or C0308 Stored In TCCM |
| Models: | 1999-2006 Cadillac Escalade |
| 1998-2007 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe |
| 1998-2007 GMC Sierra, Sierra Classic, Yukon, Yukon XL |
| Equipped with Transfer Case (RPO - NP8, NP1, NQH or NQF) |
This PI is being superseded to add transfer case models. Please discard PIP3526A.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Service 4WD light comes on and the condition may be intermittent and hard to duplicate. DTC C0306 OR C0308 will be set in the transfer case control module.
Recommendation/Instructions:
If published diagnostics do not lead to a correction, check all grounds for poor connection. If the grounds shown in the transfer case schematics are clean and tight, also inspect the engine grounds, as other components grounding through suspect grounds can then seek other ground paths and interfere with transfer case operation. Battery cable engine grounds as well as grounds located on the back of the engine cylinder heads and engine block are possible sources of this concern.
Also make sure grounds are mounted to the correct location. For example, a ground that should be on the frame possibly moved to the core support during a previous repair may also cause this concern.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
