NHTSA Complaint #11705363 — 2021 GMC SIERRA 1500

mechanical and electrical issues with my GMC Sierra Elevation Duramax Diesel, purchased in 2021. Despite multiple dealership visits, diagnostic evaluations, repairs, and software updates, these issues persist and have significantly impacted the reliability and safety of the vehicle. In December 2025, my vehicle was taken to the dealership for diagnostics and a third software update intended to resolve recurring engine-related faults. Throughout 2025, the check engine light illuminated on approximately 30 occasions, confirmed by at-home diagnostic scans. The same diagnostic code related to the 1) SCR NOx Catalyst Efficiency Below Threshold Bank 1 Catalyst 2 P2C7A - Engine I 2) Exhaust Gas Recirculation (EGR) Cooler Efficiency Below Threshold P14D9 - Engine has appeared repeatedly since the vehicle was first purchased in 2021. Additionally, on approximately 15 occasions in 2025, the vehicle failed to start. When pressing the ignition button, the engine screeched while attempting to turn over for 20 to 45 seconds, after which the vehicle powered off entirely. After waiting approximately 10 minutes, the vehicle would then start normally. Notably, during these no-start events, no check engine light or diagnostic code appeared, and the engine light and starting failure have never occurred simultaneously. hese same concerns were explicitly explained to service technicians during the most recent recall repair in 2025. I was informed that a software update would resolve the issue. However, the problems have continued. A similar frequency of failures occurred throughout 2024. At that time, GMC advised that the issue was likely the vehicle’s battery. Acting on this recommendation, I had the battery replaced at my expense in October 2024 by the dealership. This repair did not resolve the issue. From the time of purchase in 2021 through January 2024, these same symptoms occurred approximately 10 times, demonstrating a long-standing and unresolved defect.