I had loss of drive(high revs but no motion!) and juddering problems with my Multitronic box from about a year old. Twice my local Audi garage plugged in their computer and checked for a fault. On both ocassions they said the diagnostics could not find a problem. I understand that the sensors which look for problems cannot detect every possible fault and that in order to carry out a thorough test the garage should have done some live data tests to see how the car was behaving. Can anyone shed some light on how these live data tests work?

THe tech drives the car while the scanner is still plugged into the car. Obviously, a well trained tech needs little info from the scanner. He should know what is wrong because of his education and experience.