Skip the auto shop - Our mechanics make house calls

Q: Speedometer not working.

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Car stopped randomly and didn't drive afterwards

Hello, thanks for writing in. The computer will go into a failure mode and may not allow the electronic throttle to open if it detects a major computer or sensor fault. There can be many possible failures that will cause...

Q: my car wont shift into second gear when i accelerate, 2008 Dodge Avenger

Is the Check Engine Light on? You checked the fluid quality, but was it at the proper level? A shifting malfunction can sometimes be caused by a low transmission fluid level from a leak or a failed electrical component of...

Q: Who do you know what to replace the AC compressor or the clutch when it is squeals

Hello. I'm sorry to hear of this. If you are turning on the A/C and you are hearing excessive or unusual noise at the compressor, the drive belt is squealing, the belt jumps, or there is unexpected mechanical resistance impeding...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...