Depending on if its Catted with HFC or Catless, either way depending on amount of driving, I would not be surprised to see it take a week to throw a cat efficiency threshold code. I'd honestly be more surprised if it had thrown it immediately.Right, I expected a cel but immediately after install. Don't have a tune yet because I'm waiting on my JLT. Was told running a full exhaust wouldn't harm anything with no tune so I got it installed right away.