I have an early 2003 sedan ( with doggy door ) and I replaced my cats with test pipes that had the extentions for the secondary O2's. I've read that 2003 cars don't throw codes with test pipes, yet is comming up with "P0420 Catalyst System Efficiency Below Threshold (Bank 1)".

Did I read wrong, or is there something I'm missing?

 

I don't know why the 1st gen sedan would not get the same cat codes.

 

You can always still get the cat ineffieciency code when running test pipes.

some people have run extension out further

It could be the O2 sensor is bad also.

 

Well, turns out one of my sensors was banged up...hmmm