2002 Mercury Mountaineer check transmission and o/d off (bl

Transmission problem
2002 Mercury Mountaineer V8 Automatic 108000 miles

have a 2002 Mecury Mountaineer with 108000 miles on it. The truck runs great, no noise or anything. The other day "Check Transmission" appeared in my Message Center of my truck, as soon as it appeared my overdrive off light (O/D OFF) started flashing. Every time I drive my truck it takes about 5 minutes of driving before it pops up. I do not notice any additional noises, feelings, or shifting when it happens.


The trans fluid and other components are sealed, the only way to have them checked is to take it to a dealer. So before I spend 100 bucks having them check it, any ideas of what it is? What I can expect?

Thanks guys!