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Q: Speedometer not working.

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The transmission was overfilled causing the fluid to not cycle properly. The fluid then overheated on a trip, burned some, and the speedometer stopped working. The battery was old and needed to be replaced. To get the car started after the transmission fluid overheated I had to jump it. The power steering light came on shortly after. I took it to a dealership. They replaced the battery, drained and refilled the transmission, and replaced the vehicle speed sensor on the transmission. When I took it to an independent mechanic he claimed I needed to replace the speed sensor again. I bought a speed sensor and replaced it myself a second time as it is a relatively easy process, but the speedometer still didn't work. When I replaced the speed sensor, I noticed the shaft that transmits rotation from the transmission to the sensor didn't have a gear head on it the way some of the pictures have shown it, it just had a roughened top. Is that a problem? The car doesn't have ABS.

My car has 100000 miles.
My car has an automatic transmission.

A: The speed sensor itself does not have a gea...

The speed sensor itself does not have a gear permanently attached to it. The driven gear as it is known, should be already installed in the transmission. There is most likely a single slot that engages with the top of the driven gear. You will need to turn the sensor a little to get it to mesh with the slot. If you are doubting the gear is not turning, you could put both front wheels in the air. Warning, do this at your own risk and take every precaution to be safe. Once the wheels are off the ground and the car is supported by jack stands with the rear wheels blocked with chocks, start your car, put it in low gear and look inside the transmission to see if the gear is spinning. Of course, you will want the speed sensor removed from the transmission while doing this. If it is moving, you can be reasonably assured the inner workings of the transmission are good.

If this checks out good, the next step is to check to see if the instrument cluster is receiving a signal from the sensor. The ECU (engine control unit), instrument cluster, aka (combination meter assembly) and a ground are involved with this system. The scanner will give a qualified technician a clue about where the diagnostic path should lead next.

If you would like to have a certified mechanic take a look at this for you, a certified technician from YourMechanic can come to your car's location to inspect the speedometer problem.

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