(2002 A6 2.7T)
Any Advice? While Driving the car the other day the front brake started to drag/grab and the pedal bacame Stiff and ESP light came on. I pulled over and the left front brakes were smoking. I took the car to a mechanic and he tol the the caliper was sticking and a Code for "Brake Switch" was thrown. He cleaned it up and said it was working fine. When I left the mechanic the same thing happened about 10 minutes later and got worse with time. I disconnected the ABS module with no change, still happening without ABS. Could this a caliper problem or hose/vacuum problem. Gong back to mechanic on Friday.

If ESP is coming on. And caliper is grabbing on it sown, hydraulic pressure must be being applied. So its not disconnected, or likely isn't.

Grant

Had this happen on a 1985 Audi 5000 with a 5 speed. It would just start self applying one of the brake circuits (dual diagonal in that era) as it warmed up going down the road. Found if I rapped on it lightly with the wood handle of a hammer I could free it up temporarily--that also told me pretty clearly it was indeed the master cylinder. There were no leaks or pedal dropping to the floor type things I would have normally expected.

New master cylinder bolted in, brakes bled and issue permanently and immediately solved.

Any resolution to this. I'm going through a seized caliper issue myself. Can't seem to push enough fluid through the left rear caliper.