My 93 geo prism speedometer won’t work till I get up to 45mph then sticks at 70mph. Every once in a while it will start working. Usually if it’s hot or real cold out. Already changed the filter and tranny fluid. One parts place said I need the cable with the wiring harness, the other said I only need the cable. Who’s right? Or is it a sensor?
Look under the dash to see if you can see a flexible cable going to the instrument cluster. A friend of mine has a Corolla of your vintage that had an all electric speedometer head. Since the Prizm follows the Corolla design, you might have the same. In looking at his old speedometer head, it looks like the needle is driven by a eddy current cup like ordinary speedometer heads. The difference is that there is a little electric motor driving the magnet. So the problem might be just in the head.
Even if you have a flexible cable, the problem is still probably in the head. Problems with the cable usually show up as no drive, intermittant drive, noise, or jumpy drive, i.e. the needle moves all over the place. The failure of the needle to move and then sticking indicates there is some friction in the eddy current cup, needle axle, spiral spring, or bearings.
If this is truely an all electronic head, there may be a problem with the Vehicle Speed Sensor in the transmission. I have not scoped out how it works or where it is located on that transmission.
The Speedo is most likely shot, and a is not repairable on these cars. Best bet would be to go to a Pick, and Pull junk yard. I think the going rate for a instrument cluster is $20, but you buy it whether it works or not. You only need a fillips head screw driver to remove the cluster, and takes less then 5 min as long as you got skinny fingers to reach around the back to unplug the wire harnesses from the instrument cluster.
FYI: There is no cable going to the speedo. Also the odometer is built into the speedometer as well, so if you ever would sale the car after installing a used speedometer you would need to fill out the title as odometer mileage is not actual mileage
My 93 geo did the same thing. I went to the dealers and kept talking and asking where they send their speedometers to get repaired (cuz they don’t do it there) and finally got an answer just to get rid of me. Then I went directly there (cheaper) and got a new speedometer. check out the head he’s talking about above. If okay, check the vehicle spped sensor (which is located on the firewall side of the engine at the bottom in the back.) Can look on AutoZone.com to find out the ohms/voltage it should be. They’ll even “loan-a-tool” a multimeter to you to check it. If that’s ok, get a new speedo. Mine was $90, and they pre-set the mileage for you so it’s legal.