I wonder if you could be more explicit what happened when. You mentioned you took the coach out for 3 hours and the check engine came on. I assume that was when you were driving but you also said you shut off some lights and the AC (air conditioner?) and the light went out.
Or did you drive somewhere and spend the night then in the morning start the coach and you had a check engine light? Were you plug in over night?
Anyway, if you could tell us the exact sequence of events it would help.
Sorry for your loss. We are in the NH Seacoast by the way.