I had to disconnect the battery on my A6 due to the drain hole being blocked. I obviously forgot about the radio and had to phone a dealer to get the code (second hand car with the code card removed). I received the code, but it does not work and "safe" is happily flashing away when I try to unlock. What can I do from here? I was thinking of changing the Head unit for a Blaupunkt Head unit, but have been told it will cause a problem with the car diagnostics? Is that right. The car is a 1999 A6 Avant 1.8T. Thanks in advance.