mercury mountaineer o/d light flashing?

This OD light flashing means a fault has has been sensed by the transmission control module in the electronic transmission controls, to see what this fault might be have the transmission tested for electronic fault codes that are stored when this OD light flashes, many times this code will be for a transmission slipping issue, u will not fell this most times, if the transmission has more than 60,000 miles on it have the transmission fluid and filter changed and erase the codes, they may not come back.