It is still unknown, but I believe the brakes failed. My wife was driving and making a left turn into a residential neighborhood when she applied the brake and it didn't respond, even when pushing the pedal to the floor. All that resulted was a clicking noise. The brakes failing to respond, and the emergency braking not engaging did cause an impact with a curb and sidewalk. At the same time, the seatbelt did not lock on impact or when pushing the brake pedal to the floor. The safety of the my wife was put at risk as she could not stop the car. With the cars weight and the amount of power that it has, it creates a dangerous situation for anyone around, especially in a residential area. The vehicle is available for inspection and is currently at the Tesla Service Center. There was a warning light that said something regarding the "Hold" not working and another for "Regenerative Braking." I do have the four angle dash cam videos from the Tesla of both times that it did occur.