Good morning everyone,

I have a 2011 3.5 super crew, I'm throwing a P0420 code " catalyst system efficiency below threshold bank 1" my question is, is that the sensor before the cat, the upstream or at the cat, the down stream? I have cooks green catted down pipes so i'm pretty sure that why i'm trowing the code, i know the cats are good, i just don't know which sensor may be bad. Thanks for the help y'all.

 

Downstream O2s are cat monitors.

 

Bank 1 is the passenger side if I am not mistaken and I probably am LOL.

 

This is most likely your problem, P0420/P0430 codes rarely ever appear due to an O2 sensor problem, the problem is almost always the catalytic converter itself. You have high flow cats, and while I know Kooks says they won't turn on your CEL, a little research will show that many people have just that problem. I was going to buy headers and cats from Kooks but decided against it because too many people were waiting for a fix from Kooks that at the time I last checked, seemed to have never arrived. I've asked Kooks about this issue and they declined to comment on whether a fix had been developed or how they would handle the situation if my truck threw a P0420/P0430 code after installing their products.

If you aren't already running 93oct fuel, doing so can help to eliminate P0420/P0430 codes, especially on forced induction vehicles. Checking for exhaust leaks is also a good idea, exhaust leaks can easily cause P0420/P0430 codes.