The last few days, i noticed my speedo , stopped working at speeds under 40kms. I pulled the sensor out of the diff, cleaned all the goop off, re-inserted and didnt help. Can a sensor kinda "half" burn out?

 

This is what happens when the sensor fails. Once you replace it, it will work fine, and your ABS/Brake lights will go out as well. Make sure to check the wiring in that vicinity for chafing or corrosion as well. Almost certain it's the sensor though...

 

I am having a similar issue with my speedo. How difficult is it to replace? I haven't crawled under to attempt it yet. Just curious if anyone has any tips. Thanks.

 

My truck does the same thing and the abs and brake lights are on. I thought mine was a wheel sensor because when i am driving in gravel if i hit my brakes my driver side rear tire locks up. Could this be caused by the same thing?

 

It's been a while since I have done a swap, but I don't recall any particular difficulties. I think it should take less than 20mn...

 

If your ABS light is on, the ABS is no longer functional...
So you will be able to lock up the wheels.
The main sign of a rear wheel sensor being defective is usually when your speedo doesn't work under 20mph...

 

Well I guess that would make sense

 

The new sensor shut both ABS and Park Brake lights Give yourself about a hour.....The hardest thing was trying to push the new one in all the way. The clip on the electrical connection is a pain as well....But everything works good again, even my gas milage went back up.

 

Ok, just fixed my speedo issue and figured I would write what I found for anyone else having this issue.

Problem: My speedometer stopped functioning under 40mph. As time went on this problem got worse until the Speedometer would only function above 60mph. At the Same time my Brake and ABS lights were illuminated on the dash. I DID NOT get a Check engine light for fault code.

Solution: This is very dependent on your vehicle model and setup. What I found was that if you have the 46RE or 47RE Automatic transmission your "Transmission Speed Sensor" (as it is called on the box from Autozone) will be located on the Drivers side of the transmission. It is about two inches long, and an Inch and a half in diameter, it should be facing down. The sensor costs around 18 Dollars and should fix your problem. From what I have found if this sensor goes bad it WILL throw an Check engine light and Fault code.

For those using the NV4500(myself) or NV5600 transmission, your Vehicle Speed Sensor/ABS sensor are located on the top of the Rear differential. This sensor costs around 22 dollars. There should be one nut locking down a tab that holds your brake line and ABS wire, under this nut you wil find a large nut, I found it best to use a crescent wrench, Preferably a deep well socket if you have the correct size. Remove this nut and you can remove the sensor. This is somewhat difficult due to the rubber o-ring sealing it in place. Once you have removed it you will find it is much easier to bring it closer to you, in order to disconnect the wire. Reverse this process for install and you will be good. 10-15m job total. Both my lights cleared immediatly and I am back in business.

I hope this will help anyone who experiences this difficulty. As always any further information or correction is welcome. Thank you

 

AFAIK, all 98+ trucks use the RABS sensor for speedo. 94-97 use the sensor on the tranny (2wd) or t-case (4wd). I have a '94 NV4500 in my dually, and it has the speedo output on the side of it. I'd have a look at my '95 2wd 47RH to confirm that if I had it at my house.

 

My problem is when I turn the key on it pegs my speedo and clicks off miles with the truck not even running. I have changed both sensors the one on diff and the one on the tranny and neither fixed my problem.
Any help would be appreciated.

Thanks