nfn knows what he's talking about, so do some searching and see what you can find. In addition, in my personal experience, anytime I have come across a P0420, it has been a cat. Doesn't happen often, but haven't had a comeback yet. But you're in a good position to get it replaced for free because federal law puts an 8 year/80k warranty on it. Unless Acura hassles you about the exhuast you speak of, there shouldn't be any issues. Keep us posted.