It looks like I might need a new Cat for my 2005. I get intermittent CEL of P0420, when it gets at or below ~40F. The rest of the year it is fine. Though I am also hearing a rattle at low speeds. Don't know if it is parts in the honey comb has broken up, or if it is a random heat shield. This is the third winter I have had this issue. I am going to test a few things out, though if it is the Cat, do we have a forum vendor that offers a good price on OEM CA approved cat?