NHTSA Complaint #11710159 — 2021 GMC SIERRA 1500

Unexpected rear wheel lock-up at 29000 miles. While engine braking from highway speed onto an off-ramp at approximately 50 mph, the rear wheels unexpectedly locked up. Due to prior rear brake actuator issues, I suspected the emergency brake had activated without my input. It was only momentary, and no fault codes or warnings were displayed. It happened again under the same circumstances two months later, with no fault codes. On May 9, 2025, the check engine light came on, and I scheduled service. The dealer addressed a recall regarding the transmission by installing software. In August 2025, I received a letter from GM regarding recall N242454440 for excessive wear in the transmission control valve, which was causing rear-wheel lockup. On October 31, 2025, while towing a small enclosed trailer at 70 mph on the highway with cruise control engaged, the truck suddenly decelerated, and I was nearly rear-ended by a semi-truck (no brake lights to warn them). The truck would not go over 50 mph unless I was going downhill. The transmission would not shift into higher gears. I returned it to the dealer, who checked the computer and found no record of the incident, so they said there was no problem. They informed me that the new software was designed to limit the truck's speed if a potential lockup was detected. This recall did not fix the transmission problem or the safety issue. It was simply a way to avoid costly repairs. There is a problem with the physical transmission valve that, for me, resulted in an extremely dangerous situation. The NHTSA needs to take this issue seriously and require GM to replace the prematurely worn valves in the affected vehicles.