The contact owned a 2021 Mercedes-Benz GLB35. The contact stated while driving at 35 MPH, the brake pedal was depressed; however, the vehicle failed to stop as intended. There was no warning light illuminated. The contact stated that neither the dealer nor an independent mechanic was contacted. The vehicle was not diagnosed or repaired. The contact stated that the vehicle was serviced months before the failure. The manufacturer was not made aware of the failure. The failure mileage was approximately 52,000.