2002 Chevrolet Cavalier • 4 cylinder Automatic • 212,000 miles

The speedometer will work for a short time then go crazy and then stop working. It is not the speed sensor. What can it be? Thank you.
September 14, 2011.

The speedometer can go bad itself.
I had one stop working because the odometer gears got bunged up. It actually melted.
In your car the speedometer siognal puts out what is called a Hall Effect and it is used for fuel management and the cruise control.
Have you had any problems with either?
If not, it is a fully electronic signal and can still affect tannsmission shifts and anything dependent on a speed signal, (if it is picking it up from speedometer as oppsosed to the speed sensor.
Have you changed the tire and rim sizes?

No problem with fuel and the car has no cruise control. But it does effect the trans shift. When the speedmeter is working, the car sifts fine. But when it starts jumping, the trans sifts up and down, or when the speedmeter stops working the trans will not shift at all. Is it the speedmeter? The speed sensor is good. New Thank you

Sep 14, 2011.
Yes, the car computer is feeding from the signal somewhere between the sensor an speedometer to tell the transmission when to shift to save gas or for performance. More than likely, the signal might go into the computer then get split and wait for feed back form the speedometer. This is because you can overide the system and shift manually at the speed you choose, (until the rev limiter hits).
So, you probably have a problem with the speed omter. Speed sensors are less complicated and have one moving part and a pickup for the radial signal.
Good luck and let me know how it turns out. If you get a used one, get a Haynes manual or a dealer to the you how to test it.

Thank you so much. I will let you know how it goes. Have a great day.

Sep 15, 2011.
No problem. You are quite welcome and it will be interesting to see what comes of this.