I have had a problem with my S3 since October 06!! The back end felt like it was locking up. Was misdiagnosed by Audi Hitchin twice. Haldex Diff!! And then the Controller. It's been to 4 different Garages One was a Diff specialist who gave the best info and price! Only charged me £50 to swap a second hand Diff over. He advised that the fault was not mechanical but was electronic. After 5 Months the car going from garage to garage the car went to Vagtech near Milton Keynes they diagnosed the fault to be a faulty ESP Control unit, a second hand one was sourced and I finally have my car back running sweet as a nut!! Can not believe it's been off the road so long. So thanks to Vagtech I am back behind my understeering mean machine LOL (getting the suspension sorted once I have some money again!) I can not recommend John and Greg at Vagtech enough really friendly lads, and really know their stuff!! http://www.vagtech.co.uk/ Just to add there were no error lights or codes hence why no one knew what was wrong with her. It's like buying a new car having her back!!