NHTSA Complaint #11668873 — 2021 GMC SIERRA 1500

In December of 2024 the engine started not being able to reach full power. This would happen intermittently and there would be a check engine light that would come on when this was happening. In January of 2025 I had the code pulled up by a mechanic at a local shop and this mechanic actually spoke to the service manager of the GMC dealership who said it was covered under the 100,000 mile power train warranty. I took it to the dealership who then told me the diesel mechanic was backed up and I would have to schedule repair for February. I had also received a recall notice in the mail for another issue so asked about taking of both things at the same time. I made the appointment for mid-February so had to deal with reduced engine power for several weeks.The dealership had my truck for several days and a recall was fixed and I thought the reason for the reduced engine power had been fixed also. I had received a phone call from the service representative about an issue that would cost over $1200 that I declined. I did not realize that this was actually for the main issue. I was still thinking the reduced engine power was under warranty. I got my truck back but then the next day the check engine light came on again and the engine power was reduced again. I immediately called the service representative who then told me only the recall had been fixed and that the reason for the reduced engine power was not fixed because I had declined the service. I was totally confused and didn’t understand what happened. This is when I was told that the reason for the reduced engine power was due to a coolant control valve, which was not under the powertrain warranty. I pushed the issue and wanted answers as to why the service manager himself told the mechanic that it was under warranty and was told that the service manager is not a technician and they rely on what the technician says is the problem. And this problem was not covered. I finally gave in and got it fixed and paid $1788.