o2 sensor on 1998 Ford Mustang

check engine light is on and has custom exhaust, can that be it?

Asked by for the 1998 Ford Mustang
I had the same promble (check engine light). I stop using cheap gas and after 3 tanks of gas (plus), the light went out.
2 answers
It could be the CAT if it was removed i would get a diagnostic to see what the problem is autozne does this for free.