NHTSA complaint #11422144

Owner complaint summary

This new 2021 GMC Yukon Denali we purchased on June 2, 2021 has a very sophisticated controls system that includes a feature, entitled "Brake Assist," that is designed to detect "rapid brake pedal applications due to emergency braking situations and provides additional braking to activate the Antilock Brake System (ABS) if the brake pedal is not pushed hard enough to activate ABS normally." "Brake Assist disengages when the brake pedal is released." After I left the dealership (June 2nd), I noticed that the "Service Brake Assist" light had illuminated on the Driver Information Center (DIC). I pulled off the road to check the Owner's Manual, and then continued home trusting that no immediate hazard existed. I subsequently set up an appointment with the dealership for a checkup. A week later, the dealership downloaded a new software package from GMC. The Brake Assist light did not appear when the engine started, so I left for home (50-minute drive at moderate speeds). Enroute to my home, I stopped at a store and turned the engine off. Started home a few minutes later. While accelerating past 45 mph, the brake system independently engaged, which threw me against the steering wheel and into the windshield. As the SUV decelerated through 20 mph, the brakes automatically released. I was not hurt, nor did I lose angular control of the vehicle. I completed my drive home and parked the Yukon normally. Did not drive it again until returning to the dealership a few days later. This second visit did not bear fruit. After significant explorative work, the lead mechanic drove the vehicle several miles under a multitude of conditions, but could not duplicate the problem or get the light on the DIC to extinguish. At my request, the dealership returned possession to me with the light still illuminated. I have driven the vehicle several miles since then with the "Service Brake Assist" light still illuminated. I suspect this is a GMC software problem.