Originally Posted by focusZX505
I am emissions certified and In IL what they told me about people like us" that cheat the test" is that is to small of a percentage to worry about
So if ur in IL and the tune disables the rear O2 you'll be fine
I have to admit that I have gotten ~same replies from some testers in STL. As long as you don't throw an OBDII code (which in MO goes straight to the state. Not sure about other states) you should be fine. So agree!