2011 AUDI A3 Steering Problems

ESP malfunctioned while driving on highway: tires braked several times rapidly on one side without warning, making car difficult to control. Immediately took foot off gas and had to steer out of a small fishtail. At the time I was driving at normal speed, not cornering aggressively or anything, on a smooth dry road. In heavy traffic or on a wet road this could have resulted in a crash. On just a couple occasions shortly before this occurred, while going around corners at highway or near-highway speeds there was a sensation that the steering direction suddenly "slipped" a notch, with a sort of thunk from the tires. At the time I attributed it to unseen road bumps, but after experiencing the more serious failure I realized it was the same asymmetrical braking just on a smaller scale. No warning lights gave any indicator of this dangerous sensor fault. During the...