I have these two codes, P0421 and P0431, on a 2000 A6 Avant. Are the catalytic converters warranteed separately somehow for a longer period than the car? Or is there another repair that can be tried before replacing the converters?

 

Clear the codes and see if they return.

 

They do return usually in a day or two. This most recent episode was this week. I had the codes reset on Thursday, they returned on Friday morning after driving only about 15 miles.

 

converter warinty is 8 years and 80,000 miles.
Try running the BG induction cleaner through. ( you need to find a shop that sells BG services)
MY friend did and the codes never came back, it seems the cleaner cleaned out the cats also.

 

Thank you. I will look for a shop that does that.

I am beyond the mileage limit for the cat converter warrantee: too bad.