Toyota Repair: Corolla 93 Overdrive light, light flashes, speed sensor

Question
Hi Ted,
I would appreciate your advise about my problem on my 1993 Corolla. After driving for about 20-25 minutes at speeds of about 45-60 mph, the overdrive "off light" flashes on and off maybe every 3 seconds. Sometimes it does not come on at all.
When I switch the overdrive off, the light come on. But when I turn the overdrive on, the overdrive off light flashes again. Is this a serious drivability problem.
Thank you.
John

Answer
Not Ted, Its Mike.

you probably have a bad speed sensor in the trans.
When the ECU sees a difference between the speed sensor and the speedo it will flash the light.
Need to scan the car for codes and retrieve to get an idea where the fault lies.

Mike