Ford explorer O/D off light blinks

The “O/D Off” light starts blinking on my 2002 Ford Explorer for no apparent reason. At the same time a check transmission message is displayed. It is a four wheel drive with automatic transmission. This seems to happen after I have been driving for at least half an hour. Even when the light is on the overdrive can be turned on or off normally and everything else seems to work fine. If I stop, turn off the ignition and start again the light and message go off. Does anyone have an explanation for this or a recommendation?

The computer needs to be scanned to determine what’s causing the OD light to flash and the Check Transmission to be displayed.

Tester