How many converters does the 2001 Audi A6 have?

I have a 2001 audi a6, the check engine light came on and I took it for a code check and it came out to be the catalytic converter. I recently replace them and the check engine light is still on, someone told me that the audis have 4 cataltics 2 on the bittom and 2 on top. Is this true?|||Yes it has 4 total 2 pre and 2 main. They are sold as units however so if you had the left side replaced they would have done both. Where did you have them replaced at? I guess a muffler shop could weld in a single unit and not replace the pre-cat. There could be other reasons the light is on also.|||No, they have 4 O2 sensors. I bet it needed O2 sensors as opposed to a catalytic converter. It does however, have two catalytic converters.