The parking aid system is standard on highline models and optional on others, utilizing four ultrasound sensors in the rear bumper to measure the distance to objects behind the vehicle, alerting the driver with acoustic signals from a buzzer in the rear luggage compartment, with frequency increasing as objects get closer. It features a control unit and self-diagnosis program, necessitating a visit to an Audi dealer in case of faults. The control unit is situated in the luggage compartment behind the right-hand trim panel; to access it, the ignition and all electrical consumers must be switched off, and the ignition key removed before removing the trim. The wiring plugs should be disconnected, and the unit unclipped from its mounting bracket, with refitting being the reverse of removal. To access the range/distance sensor, the rear bumper must be removed, followed by disconnecting the wiring and releasing the lugs to pull the sensor from the bumper, with refitting requiring firm pressure until the retaining clips engage. The warning buzzer, also located behind the right-hand trim panel in the luggage compartment, requires the ignition and electrical consumers to be off and the ignition key removed for access; the wiring must be disconnected, and the clips released to remove the buzzer from its mounting bracket, with refitting being the reverse of removal.