Hi i have a 2000 honda civic. Im located in California so smog rules here are pretty strict. If i buy a universal cat that doesnt have the o2 sensor located in the cat can i just put it after the cat?

 

Generally speaking, yes.

 

Generally speaking yes, but if the tech finds it they can fail you because of it. Also, the cat itself must be CARB legal.

 

Failing you because the secondary O2 sensor is welded in past the cat, instead of...wait, what? That makes zero sense. The bung is there. It had to be welded there. Whether it was welded in before it was installed or after shouldn't make a difference.