Hi guys, can anyone tell me what the e.s.p button actually does ?, Had my 2004 A4 1.9tdi quattro for around 10 months now and i am reasonably happy with it apart from an annoying turbo compressor surge/ stall noise when changing up through the gears which I have not managed to solve yet and bit disappointed with mpg (40ish to a gallon, but just wondering what this ESP button actually does, my car's back end has stepped out a couple of times where we live (muddy road/builders) but the ESP light doesn't come on at all , the ESP lights up normally when ignition is switched on and then goes out normally, am I missing something ???