2004 Ford Explorer

Transmission problem
2004 Ford Explorer 6 cyl Four Wheel Drive Automatic 164000 miles

The O/d off light came on the dash a couple weeks ago and I told it might be because I replaced just one tire. I went ahead and replaced them all, but the light is still there. It only comes on at about 50 MPH and came on sooner before I replaced all the tires. I have not been able to sense any tranny issues at all as the vehicle oeprates very well. Any suggestions on getting the warning light to not light up?
November 24, 2008.

The steps needed it to have it scanned for codes as the TCM (tranny computer )is storing troubled codes in it and letting you know that you have an issue going on and the tranny need to be checked
check tranny fluid and fuses
check the OD switch

Nov 25, 2008.