Does an aftermarket exhaust always throw a CEL, or does that mean somethings wrong with the setup?

 

something wrong with the set-up. Some aftermarket exhausts require an o2 sim or reprogramming to keep the check engine light from appearing.

 

Depends if there's a test pipe or not.

 

That's what I was going to say. I think it's pretty uncommon for a behind-the-cat exhaust to trigger a CEL.

It's when you start changing out the OEM cat for a test pipe, or a HFC that the CEL generally starts being a concern.

 

Changing a cat-back exhaust should never throw a CEL. If the cat was replaced then there's the possibility.

 

Agreed with above...just installed a new intake and exhaust and no CEL issues (minus the one very minor one I did have due to a hose being too long and getting cut, but that was intake, not exhaust).