The contact owns a 2012 Cadillac SRX. The contact stated while driving at an undisclosed speed, the brake pedal was depressed; however, the vehicle failed to stop as intended. No warning light was illuminated. The contact stated that the brake pedal was depressed to the floorboard to stop the vehicle. The contact turned off the vehicle. The vehicle was restarted, and the system was reset. The vehicle was taken to the dealer where it was diagnosed with a failed brake master cylinder. The contact was informed that the brake master cylinder needed to be replaced. The vehicle was repaired; however, the failure reoccurred. The vehicle was not diagnosed or repaired by an independent mechanic or the dealer. The manufacturer was not made aware of the failure. The failure mileage was approximately 110,000. The VIN was unavailable.