I was just thinking about this today seeing as I have let my car run rich for quite sometime now(code 1222 and 1221), I was wondering if a bad cat would end up throwing a code later down the line, because isnt the O2 sensor before the cat (I dont know how the computer would register a bad cat)? I wonder if you were in an area that didnt do emissions if you could just let the cat go..... and what would happen? Not that anyone should feel good about doing that! Just wondering about a few things.