I have question, someone already answered this but my friend is mechanic and the dude that answered has his back two cats cut off and left the front ones on and he said he hasn't thrown a code for a year, I want my check engine light off with still having the 02 sensors.... And if I can't take off back cats without throwing a code, then what kind of programmer will possificly tell my car how much oxygen I'm burning so that my car will get the most efficientcy with a bad ass sound? It's a show car, and I want that little bit more loudness to my mustang cobra. Someone please help me out.