Overdrive comes on and off whenever it feels like it. What can cause this? on 1998 Ford Taurus

Check engine light comes on when this happens and speedometer goes crazy.

1 answer 4 comments
you have trans problems. take it to a shop and have the codes read.aamco will do it for free but get several opinions on repair and prices
It's been this way for 2 years. When put on diagnostic machine, said speed sensor, transmission or electrical.
yes it only tells you the bad circuit not the actual sensor or problem. thats or job to determine. the repair could exceed the valve of the car in your case,so you might leave it alone for now
If left alone will it cause more problems to the transmission?
possibly but the cost of this repair could go from 400.00 to 2500.00 depending on what's wrong.