98 civic ex - d16y8 CEL is giving me a P0420 code (Catalyst System Efficiency Below Threshold) 1. does that absolutely, positively mean bad CAT? Could it be a bad sensor (secondary o2 sensor, right?) in the CAT? How could I test the difference? 2. shopping for a new CAT - every website seems to have the same stuff and the same price range: $131 - $550. How do I know I'm getting the right one? I'm pretty sure I want the one with the "2-Bolt Welded Type Inlet, 3-Bolt Welded Type Outlet" just for simplicity sake, but what about brand? There's Eastern, Cato, Magnaflow, DEC, Bosal, etc. etc. Any suggestions for brand or where to get it? Any advice what to look for or avoid? Thanks!