Ford Maverick Automatic Gearbox Fluid (ATF) Problems

The overdrive light flashes steadily on and off after the car has been driving for some time under load (eg after 1 hour of towing a horse box at 50mph). The flashing light is not there the following day, tt does not happen under any other...

When starting and cold gear change ok , after 5/10 min driving OD light flashes on dash , and sticks in gear until you lift foot off acelerator and then it changes up , any suggestions please as to what the problem may be ,