Anyone know? I was under my car changing the oil and tried to find them. My manual says that I have four. I have found 2 but they appear to be before the cats. I have a 2000 A6 2.8 Avant. SO are the Cats right after the the exhaust flex connector? Or are the CATS in the engine compartment? Are the two I found the rear ones? Any Ideas would be appreciated .

Yes you have 4 of them, pre and post O2 sensors, you found the rear ones the other 2 are way hidden at the rear of the engine

And i have to ask WHY??

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In answer to your question why, I am probably going to pull out my CATS and replace them with a test pipe. I dont have emmissions in my county and my CATS are dead and I do not want to pay 1400 to get them replaced. After I do that I probably will also do some high-flow exhaust work. I also got the Idea from the DIY forum under the post testpipe CEL(or somethin like that). Why do you ask? Should I not do it?

Oh yeah, I forgot if the ones I found are the rear ones where are the CATS. I have bentley manual, just havent looked at it yet, but if you would like to tell me any way that would work.