I have been trying to solve my Catalyst problem only to find out that my 2002 A6 4.2 has a system the dealer says does not belong on my car. There are pre-cats on the car and the dealer says they shouldn't be there. Also there is one oxygen sensor that isn't where it should be according to the picture the dealer shows for my car. The last sensor is located in front of the cat and the picture shows it after the last cat. The trouble code I get is 16815 pre-cat warm up bank2. This applies to both banks. Needless to say I can't pass smog and California is the strictest state.