Last week, the third week of owning an A4 (B8 platform 2013 model), my wife experienced a hold-assist or brake issue. She was on the ramp down to basement carpark (Level B1) with Hold Assist activated, she stopped at the barrier to collect the parking ticket, but stopped a little too far. So she unbuckled and noticed the "P" turned from green to red, picked up the ticket and buckled back. Put her foot on the accelerator a little, and then her foot on the brake trying to moderate the speed. To her horror, the brake became hard that she couldn't depress it at all, while the car was going down at fairly high speed! She had no choice but navigated the car down from B1 to B3, until a level section of about 30m, the car came to a full stop! Thanks goodness, it was a weekday and there wasn't a car or persons in front during the whole course! Otherwise, I couldn't imagine how much damage it would have caused... She restarted the car, everything went back to normal.
Took the car to Audi, they did the test and tried to repeat it, but in vain. I was advised to go to another centre where they have better testing facilities. Did that on the next day, again, they did all sorts of emulation, but the problem didn't surface again. The audi technicians said it should not have happened, unbuckling would jam the brake and the car should not have moved, if it was due to unbuckling of the seat belt. But it did.
I read from rac.co.uk that many had experienced brake failures of similar symptom with earlier platforms, and there were problems with the plenum chamber, water in servo/cyclinder, vacuum pipe issues or due to cold weather that icing affected the water drainage. But we live in Singapore and the car was only 3 weeks old!
Anyone have had similar experience? What was your resolution? My wife now has a phobia about this car and i stop using HoldAssist.