U.S. auto safety regulators have expanded their investigation into General Motors' electronic brake system following a surge in consumer complaints.

The National Highway Traffic Safety Administration (NHTSA) widened its probe after receiving additional reports of brake boost failure, extending the review to cover all GM vehicles equipped with the eBoost braking system.

Here's what you need to know: The agency's Office of Defects Investigation initially opened a preliminary evaluation in April, prompted by complaints about brake boost failure in the 2023 Cadillac Lyriq.

As new complaints piled up, NHTSA launched a deeper analysis to assess the safety risks posed by eBoost system malfunctions during vehicle braking, while also broadening the scope to encompass every GM model fitted with this technology.

Drivers have reported symptoms including a stiff brake pedal and a "brake system failure" warning appearing either at startup or while driving.

Since the initial assessment began, regulators have received more reports of brake boost failure, with some incidents not matching the "spindle failure" explanation provided by General Motors.

GM had previously stated that if a spindle breaks, the vehicle's anti-lock braking, stability control, and traction control systems would remain operational until the car comes to a complete stop.

However, incident reports from drivers indicate that brake boost can fail instantly rather than waiting until the vehicle halts fully. NHTSA noted that a sudden loss of brake boost during operation could lead to longer stopping distances.