Don't see why I keep getting this code regarding the cat when I still have my stock exhaust (yes, stock downpipe, cat, and catback). I have a custom dynoflash and works drop in filter and haven't had any problems, but this CEL comes in every 2-3 weeks and it annoys me (I have my own OBD2 scanner, so I can erase it at my leisure).

Today I was driving with my friends and they mentioned to me that I shot out a little bit of black smoke when I sorta got on it, but the car runs great, should I be concerned or anything? Maybe my secondary sensor is loose? Only have about 3400 miles on my IX.

 

I got the same code after I installed my Greddy TI. It comes on every 2-3 weeks also. I have about 5000 on my IX. I just installed hte mechanical O2 fix, and so far no code..

 

Either your post cat o2 sensor is loose(one after the cat) allowing it to see O2 and thus making the computer think your cat is dead,or you have an exhaust leak in same area,or possibly your Cat is dying.I would look for an exhaust leak if I were you though

 

I checked for leaks for mine, there were none... it only came on after my Greddy TI, but after the o2 fix, it went away...
oh well, who cares, the rear o2 does nothing anyways. The mechanical o2 fix seems to be working so far...

 

He was probably talking about me. I'll check under there to see if my sensor is loose or if I may have an exhaust leak tomorrow.

 

Well it doesn't look like I have any leaks and the sensor is fine, but upon further researching, I think I figured out what it may be. My dealer changed my oil and they overfilled it (its like half an inch above the maximum notch) and I complained the day I got it, but in their defense, they said its because the car will naturally burn some oil and that I won't complain in the long run...

Anyways, I was looking at this site which makes my OBD2 scanner and they make an interesting statement at http://actron.com/faq_detail.php?pid=16151&id=13

P0420, P0430 Catalyst Efficiency
Code P0420 indicates that the exhaust gas exiting the catalytic converter is too similar to the exhaust gas entering the converter. A faulty or overloaded converter due to an unbalanced air/fuel mixture can cause this condition.

Common causes include incorrect fuel pressure, an EGR system malfunction, an MAF sensor malfunction, intake or vacuum leaks, incorrect cam timing, a bad PCV system, misfires, injector problems, cooling system problems, a restricted air filter, a head gasket leak, or a high oil level.

Do you people think its possible that may be the problem in which I am getting the P0420 with my stock exhaust? I'm going to drain some tomorrow to see if it remedies it, but I want to see from you Evo guru's if you think this is accurate.

Thanks.