The National Highway Traffic Safety Administration is expanding its investigation into GM's electronic braking system after receiving several complaints.

The administration's office of defects investigation opened a preliminary evaluation in April after receiving complaints about a loss of brake assistance in 2023 MY Cadillac Lyriq vehicles.

The NHTSA is opening a further analysis after receiving more complaints to assess the safety-related consequences of a failed eBoost system when braking. The agency is also expanding the scope of its investigation to encompass all GM vehicles that use the system.

The complaints allege a hard brake pedal, followed by a "Brake System Failure" message at start-up or while driving.

Since opening the evaluation, the agency has received more reports of loss of brake assist, some of which have described issues inconsistent with GM's description of a spindle failure.

GM has stated that in the event of a spindle fracture, anti-lock brakes, stability control and traction control remain functional until the vehicle comes to a complete stop.

The driver reports allege an immediate loss of brake assist functionality instead of the loss occurring after the vehicle comes to a complete stop. The sudden loss of brake assist during braking could result in extended braking distance, the NHTSA said.