NHTSA Complaint #11718970 — 2021 GMC SIERRA 1500

The failed component is the engine coolant control valve on a 3.0L Duramax truck. The failure has been documented and confirmed by both an independent mechanic and an authorized dealership. The malfunction creates a significant safety hazard. Without warning, the truck will suddenly enter a reduced engine power mode while traveling at normal highway speeds. When this occurs, the vehicle will not allow acceleration beyond approximately 50 miles per hour. This is especially dangerous when operating on roadways with speed limits of 70+ mph, as the sudden and unexpected loss of power places myself and surrounding motorists at risk. The problem has been reproduced and confirmed by Steele GMC in Round Rock, Texas. In addition, the vehicle has been inspected by an independent mechanic, both of whom verified the coolant control valve failure. Prior to the initial occurrence of the failure, there were no warning signs. Once the malfunction occurred, the check engine light illuminated. General Motors has issued Service Bulletin #25-NA-185 (revised December 4, 2025), which addresses engine coolant control valve failures on 3.0L Duramax vehicles and outlines the proper diagnostic and repair procedures for this exact failure mode. This bulletin applies to 2021–2026 3.0L Duramax trucks. Additionally, GM has implemented Special Coverage program N252508341 for 3.0L Duramax coolant control valve failures, which extends coverage up to 15 years or 150,000 miles when diagnostics confirm the failure condition. Despite the fact that my vehicle’s documented failure matches the exact conditions described in the above-referenced service bulletin and special coverage program, I was informed by Steele GMC that my specific VIN is not included in the warranty. Given the documented safety risk, the confirmed diagnosis, and the existence of official GM guidance addressing this precise issue, I respectfully request this be reviewed and appropriate coverage or corrective action be authorized