Welcome to the forum.
Your '99 4.0l will have a 5R55E automatic, a 5-speed trans.
Just a quick background, 5R means 5 speed, 4R 4-speed
44E were used on Ranger 4cyl and 3.0l V6s
55E were only used with 4.0l engine, it is a heavier duty trans.
E stands for full Electric shifting.
The previous 4R55E was of course a 4-speed with full electronic shifting.
Ford added a shift to OverDrive(OD) while still in 1st gear to add a new 2nd gear, and renamed the transmission a 5R55E.
So you have shifting like this, 1st, 1st+OD, 3rd, 4th, OD = 5-speed tranny from a 4-speed tranny, very clever these Americans, lol.
Does hard shifting involve "2nd" gear, which needs OD?
Flashing OD light usually means an electrical problem, and computer may put transmission into "limp" mode, as in "limp home", which will cause hard shifting.
And the electrical problem doesn't have to be in the transmission at all, could be an engine sensor is out of its range so computer switches system over to "limp" mode.
An Auto Parts store will Read the Codes for free, WRITE THEM DOWN, exact code numbers are very helpful, "I think code number was............" is worse than no code at all, lol.
And code numbers that are not used are also important.
So the OD light flashing means computer has detected a problem in the engine or transmission.
Doesn't mean more or less than that.
You fix it by checking out what the computer has to say, the codes.
Turning key off and on , restarts/reboots the computer so OD light won't flash until the problem is detected again, this usually means some sensor is going out of range or a control(solenoid or valve) is not responding as it should over a period of time, then the flashing OD light returns.
Google: 5r55e od light flashing
Many posts about this symptom and many different solutions depending on the actual problem, which is what you need to find out first
Explorer used the same trans as Ranger 4.0l, and same system/control
Last edited by RonD; 08-12-2016 at 01:21 PM.