Customer may report sporadically hearing the parking brake being actuated after the vehicle has been switched off. If the customer does not identify the sound as the sound of the parking brake being actuated, he or she may simply complain of hearing noises from the rear brakes. Ignition is switched off. Steering is locked. Park is selected. Parking brake is not engaged. If the electro-mechanical parking brake is not operated for some time, the free play between brake pads and brake discs increases because of normal brake pad wear. The parking brake control unit performs an automatic correction about every 621 miles (1,000 km). On A8 models, the brake pad thickness is also calculated.