Could it be my Speed sensor?

Question

I have a 95 mercury sable 3.0. When i drive it the only time it reads the right mph are if i am constantly accelerating or constantly decelerating. if i try to hold it at a constant speed it jumps all over. from 2 to 35 down to 12 and so on. It wouldnt really be a problem but since my whole car is on an electrical system it has been linking to the trans so when it reads that im doing 12 for example it will shift down to first gear while im still doing 45. is it my speed sensor? or any other ideas?

Answer 1

If it was the speed sensor you would be getting an engine code. It's more likely the speedometer. One way to tell is if you have a cruise control. If that worked ok, the speed sensor is ok.

Answer 2

would appear to be a faulty speed sensor. Many newer cars use electric speedometers and not the cable driven ones seen on older vehicles and give erratic readings as they reach the end of their service life...