I searched old posts...but this code came up for A4's. Is it the same for S4's? The code is P0431 warm up catalyst efficiency below threshold (bank 2). Does this mean I have to replace the passenger O2? or what does it mean? Is it difficult to do myself? Thanks for the help guys.

 

sure sounds like a bad 02. Stock exhaust?

 

Yup....stock exhaust....but when I went to start the car this morning.....the CEL is not on anymore. Can someone explain this? Does it turn off when it has run three to five times without problems and automatically shuts off or something? Thanks.

 

there are some codes that can turn off if they do not see the problem anymore. If if comes back and stays ur gunna need new o2s