Speedometer not working why?

Hello,

It sounds like the PCM went bad but to be sure lets do a wiring check between the VSS and the PCM. Here is a guide to help us and the engine and transmission wiring diagrams so you can see how ti works and which wires to test. Check all fuses as well.

https://www.2carpros.com/articles/how-to-check-wiring

If the fuses and wiring checks out I would try a used/rebuilt PCM. Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

Cheers, Ken

Will do, I will let you know the results this weekend.

Please do.

Did a recheck on wires and found the wires to the ABS sensor on the rear differential broke. I fixed them and the ABS light overdrive light both went off but the speedometer works fine until you reach 50 mph then starts bouncing around like crazy. Gas gauge still does not work. Thinking sending unit, needle moves from full to well overfull when I turn the key on transmission still has a pretty firm shift and shutter from time to time on the highway.

Maybe filter fluid change on transmission?

Is the VSS sensor OEM? I would install the old one if not. Cheap sensors can make the needle bounce. It does sound like the fuel level sensor for the fuel gauge issue. To confirm the issue remove the fuel gauge wires and ground it, (yellow and white wire).

I cannot find a yellow and white I have a brown and white and yellow and green. Then an redish orange and thick black. I assume those are fuel pump, the other two wires give no signal on my meter, and gauge does not react when they are grounded.

Oh, put the original VSS back in and all other problems fixed. Speedometer and odometer work fine. ABS light is off and she shifts normal. Thank you for the help. All that is left is gas gauge.

Gas gauge repaired, I bypassed the yellow and green wire and the gauge started working. Every issue I had was faulty wiring.

Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help

Cheers, Ken

My 95 ford was running along fine on a sunday night. It snowed, I did'nt drive it again till Tuesday. Suddenly my Tranny was shifting extremely hard from 1 to 2 and moderately hard from 2to3, My power door locks stopped working, my speedometer stopped working, and my dome light stopped working. Mechanic told me to try speed sensor, bought one, that part may be on my truck but it sure aint on my tranny! Tried replacing ABS sensor. Took my rear diff cover off looking for some sensor that my dads bronco has in there and had been replaced for same probs. Dont have one! So my questions are this, Could it be a fuse or rheostat? Something in the main power distrubution box? And where in the Heck is my speed sensor located? Somebody that had the truck before me installed electric fans, poorly, we had to rig a switch for them so maybe he messed up something else? He went through Power ditrb box. Also dont know if this makes a difference but the truck is a 95 built 10-94.
Any ideas? Please help, layed off mom with 3 kids! Really tryin to fix this myself!

The truck ran all right until it snowed, could soem wires have gotten wet and shorted. Check the battery connections and clean if needed. Also check the ground wires. Some look all right but are not getting a good ground. With everything stopped working after the snow, that what I would think happened, I don't see why the transmission, the door locks, dome light, and speedometer would stop all the same time unless something happened to the electric. Make sure the fuses are good after checking the connections. There should also be a fuse box by the front fender under the hood.

Thanks so much! I will check those things. I had already decided it had to be electrical as I noticed more n more things not working. Had suspicions of the power distribution box. Now I will also check on wiring! Thanx again!

While driving the other day, was going downhill and noticed my speedometer and electronic odometer quit working then tranny down shifted with a jolt, when sped up transmission now shift at 2500 rpm but with a hard jolt, any ideas

The vehicle speed sensor is located on the differential housing in the middle of the third member. Here is a guide to help you see what I am talking about.

Check out the diagrams (Below)

Please let us know what happens.

Cheers

Yep that did the trick I got a new sensor for 34.99 and it fixed the problem thanks for the tip this site is great.

1994 F-150 5.0L 4x4. Speedometer and odometer went out and transmission is knocking when it changes gears (auto). I changed VSS but same problem. I also changed fuse under dash with no luck. Any suggestions? Could it be one of the large fuses under the hood in the connector box?

Check the fuses to make sure, but your first guess is mine too. If the check engine light came on, have the computer scanned to determine if there is a code relating to the trans. If there isn't a light, check to see if there is power to the speedo / odometer. If there is no power, start tracing wires back to the pcm to see if anything is disconnected, corroded, or damaged. You may actually want to start at the VSS to see if there is power there and trace that back. It will save time. There is one other thing you need to check. Under the dash (behind the fuse block) is a module known as the GEM. On many of these model year vehicles, the windshield would leak (not enough for you to see) and get the GEM wet and eventually cause it to short. Check the module for any evidence of water getting to it. One last thing, if you haven't, you may want to try a different VSS. With all the importing of products from other countries, there is a chance you got a bad one. It happens more than one thinks.

When I press on the gas between 1-5 mph the speedometer rises all the way to 80. It goes back down when I brake. Also, where it shows how many miles I have, it blinks 230,000 and error right after the display of miles. How do I fix the speedometer reading?

Good afternoon,

Do you have a scan tool to be able to read what the ECM sees from the speed sensor?

That would be the way to tell if you have a vehicle speed sensor issue or a dash cluster issue.

The sensor sends a signal to the ECM and then the ECM sends that signal to the dash cluster.

Roy

PURPOSE
The Programmable Speedometer/Odometer Module (PSOM) provides a vehicle speed signal input to:
- Powertrain Control Module (PCM)
- Speed Control Servo Amplifier
- Instrument Cluster

The speed signal is used by the PCM to determine transmission shift points and torque converter clutch operation.

OPERATION
The PSOM receives a vehicle speed signal from the Differential Speed Sensor (DSS) on pin 4 DSS input, and pin 5 DSS return. It converts this signal to a standard 8000 pulses-per-mile speed signal output. This output signal is sent to the PCM on pin 3 PSOM (+) and pin 6 PSOM (-).

The PSOM receives two power supply inputs. Pin 1 receives a continuous 12.0 volt input while pin 2 receives a 12.0 volt input only when the ignition switch is in run.

RELATED DIAGNOSTIC TROUBLE CODES

DTC 29/452 PCM detected an error in the PSOM output signal.

The Vehicle Speed Sensor (VSS) is located on the rear axle housing.