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
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.
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I had the same promble (check engine light). I stop using cheap gas and after 3 tanks of gas (plus), the light went out.