Vehicle Information Make/Model:GMC Sierra Year: 2014 Mileage:126,467 Customer Concern The customer reported that the instrumentation cluster on their GMC Sierra was behaving erratically, especially while driving over bumpy roads. This issue was highly duplicatable and presented a significant safety concern. Initial Inspection During the initial visual inspection, the following observations were made: The instrumentation cluster exhibited erratic behavior when driving over uneven surfaces. The issue was easily replicable by rocking the vehicle in the parking lot, indicating a potential physical fault. The Diagnostic Process Initial Diagnosis and DTC Retrieval Connected the scan tool to retrieve Diagnostic Trouble Codes (DTCs). Detected CAN communication faults across every module in the vehicle, indicating a systemic issue affecting the entire network. Physical Inspection Conducted a thorough visual inspection of the vehicle's undercarriage and suspension components. Identified a broken shock mount at the rear of the vehicle, suggesting that significant stress and movement had been affecting nearby components. Chafed Harness Detection Focused on the area around the broken shock mount for potential wiring issues. Discovered a chafe in the harness near the broken mount location. The constant movement and vibration caused by the broken mount had led to the insulation wearing down, exposing the wires and causing intermittent CAN communication faults. Harness Repair and Temporary Solution Isolated the chafed section of the harness and repaired the damaged wires to restore proper insulation and connectivity. Rerouted the harness away from the broken mount to prevent further damage. This fix was implemented as a temporary solution to allow the customer to continue using the vehicle while arranging for the frame and shock mount to be permanently repaired. Technical Analysis CAN Network Impact: The chafed harness near the broken shock mount caused intermittent short circuits and open circuits, which disrupted the CAN communication network across all modules. This resulted in erratic behavior of the instrumentation cluster and other electronic systems.

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This community exists for technicians who want to understand systems, test with purpose, and diagnose with confidence—not throw parts and hope. Inside this Skool you can expect: Real-world diagnostic walk-throughs from actual shop scenarios Electrical, driveability, and data-based testing strategies The why behind the test—not just the result Open discussion, case studies, and technician-to-technician learning This is not a shortcut group. This is not a code-reader community. This is a place to raise your standard. Our Core Rule If you don’t test, you don’t know. If your new here, and joining us for the first time feel free to introduce yourself below.