Ford Repair: Ford van tranny problem, ford van, d light

Question
I bought a used Ford '05 E-150 with a 4.7L.  As I am driving down the highway the overdrive off light starts blinking.  The transmission shift normal and the over drive kicks out like normal.  I check all the wiring connects and they seem to be solid.  Is this serious?

Answer
best advise, first check to make sure fluid level is up. Second, bring it to your local dealership to have the transmission module scanned, these trani's are not known for common problems. it could be something as simple as a computer reprogram but theo/d light flashing is an early warning light of something not right but not something you can scan for without " the sophisticated" computer