I see a lot of posts about swapping the header. My question is, how does the P0420 code even show up on relatively new cars?
I have a 55k mile FR-S and the code just popped up. It's most surely the O2 sensor because temps dropped around 20F pretty quick from one day to the next in Michigan Oct 2nd week. That probably causes the fuel to run richer. But seriously, should this happen in a barely run (for a Toyota) car? OP is in Arizona so I'd atleast think he shouldn't be seeing this problem?
Guybo - you mentioned it could be a wiring issue - can you elaborate? Would you need a header cat replacement in such a case? Michigan too has no emissions testing, so I can find parts locally with a ton of folks parting out all the time on the MI86 club.
As per posts above, I'm not going to my local Toyota dealer because they want $125 just for diagnozing the problem - I already know what the issue is. Plus parts and labor - the whole thing could run up a bill of $1200 bucks and I'm not trying to get fleeced. But the question remains as to why this should pop in a car so new and driven smoothly without any aftermarket mods.
