Hi I have a A3 2014, This happened to me a few weeks ago the message appeared intermittently but usually when i started the the car they were

Warning brake servo inoperative and

Automatic start/stop: system fault! Function unavailable
Got it booked in at Audi Halesowen who technical staff diagnosed it as the "Brake Servo vacuum sensor which was promptly change and the problem rectified.



Their has to enough of a vacuum in the servo before the Start/stop function works



Happy Days