od light flashing

I have a 1995 ford explorer 4x4, the overdrive light is flashing, the code I'm getting is 648 which is incorect gear ratio obtained for fourth gear. can any one tell me what causes this problem? thanks!

My first suspect would be the OD solenoid. I'm not sure if the Explorer has a problem with a simple little e-cllip breaking, causing the OD to not work or not, but that was a problem on some FWD Fords of this era.

If that's not the case, then it may be as simple as an shaft speed sensor problem such as the input shaft speed or output shaft speed sensor.

-Rod

my local napa store is telling me the shift solenoid is my problem I will have it tomorow. I will post back and let you know. thanks for the reply.