I just had my 99 A6 2.8 serviced, did timing belt and related parts replaced, valve cover gaskets and seals...two weeks after i got my car back the oil warning indicater lights up, the abs and brake warnings light up, and the tach needle stops working.. and ac compressor shuts off...I tested batt. and alt. and mech says they are fine??? the problem stops while driving all at once (sporaticly), all warning lights go off and rpm tach kicks on. It runs good. i'm thinking its electrical? maybe the alternater or a relay?
I had a jetta that did this right before the alternater went out. Any help appreciated.