US safety regulators have escalated an investigation into brake problems affecting more than 1.1 million General Motors vehicles, following reports of 745 incidents, including 21 crashes and five injuries. The National Highway Traffic Safety Administration has moved the probe to an Engineering Analysis, a step that often precedes a formal recall decision.
The investigation centres on the eBoost brake assist system fitted to a wide range of GM models, including the Cadillac Lyriq, Chevrolet Colorado, GMC Canyon, Buick Enclave, Chevrolet Blazer EV, and GMC Acadia, among others. The probe also covers the Acura ZDX and Honda Prologue, which are built alongside GM vehicles and share the same braking hardware. In total, an estimated 1,164,820 vehicles are under scrutiny.
The Office of Defects Investigation began a Preliminary Evaluation in April 2024 after receiving complaints about a loss of brake assist in 2023 Cadillac Lyriq models. GM has attributed the failures to spindle fractures, stating that vehicles could still be brought to a stop and that ABS, stability control, and traction control would remain functional. After those functions are lost, multiple warning lights activate and vehicle speed is capped at 43 mph.
However, the ODI says some complaints describe symptoms inconsistent with GM's explanation. Drivers report an immediate loss of brake assist functionality, rather than a failure occurring after the vehicle has come to a complete stop. These reports have continued over the past two years, prompting the agency to escalate the investigation despite no recall having been announced.
The affected vehicles span model years from 2023 to 2026. The list includes the 2023-2026 Cadillac Lyriq, Chevrolet Colorado, and GMC Canyon; the 2024-2026 Buick Enclave and Envision, Chevrolet Blazer EV, Equinox EV, Traverse, and GMC Acadia; and the 2025-2026 Cadillac Celestiq and Optiq. The 2024 Acura ZDX and 2025-2026 Honda Prologue are also included.
The escalation to an Engineering Analysis marks a significant step in the regulatory process. At this stage, NHTSA engineers examine the scope of the defect, the frequency of failures, and the potential safety consequences. The agency will determine whether GM's explanation of spindle fractures accounts for all reported incidents or whether a broader design flaw exists in the eBoost system.
For GM, the investigation adds to a growing list of regulatory and safety challenges. The company has not issued a recall for the brake issue, and it remains unclear when a decision will be made. Owners of affected vehicles have reported warning lights, reduced braking assistance, and speed limitations, though no fatalities have been recorded in connection with the incidents.
The outcome of the Engineering Analysis could lead to a recall affecting more than a million vehicles across multiple brands. If NHTSA finds that the eBoost system poses an unreasonable risk to safety, GM would be required to notify owners and offer repairs. Until then, the investigation remains open, and the agency continues to collect data on the reported failures.