I have a 2004 Ford Expedition. I just had the transmission rebuilt by Aamco and picked it up this last Saturday. I noticed an exhaust leak that was never there before. It is between the catalytic converter and the exhaust manifold. I have an appointment this Friday for them to repair it. My service engine soon light came on yesterday. Could this small exhaust leak cause the service engine soon light to come on?

 

Yes , It could be giving the O2 sensor wrong info.