I have read through some of the old posts and was looking to find out if anyone has seen where you get a PO420 code even after checking the Cat and it seems Good? I've replaced both 02 sensors and the Ck eng. light still comes back. It is the only code in the system, as well. I checked the CAT with a infared temp gauge and the Code Scanner live function(02 sensor 2 voltage). The car has always ran fine. I personally really don't give a sh*t about the code, it's just that I may sell or trade this thing soon and don't need to get screwed over the Ck eng. light being on. Any help would be greatly appreciated. Thanks