Hello,


As the title states, I am having issues with a "new" Blazer I just purchased. It's a 1998 4WD 4 door with 115,000 miles on it. My speedometer isn't operating at all. I replaced the transmission speed sensor to see if that might be the issue, however that was not the case. It looked like it was never replace before. I changed the speed sensor, took it on a test drive and it is still not working. A couple friends who are better mechanics than me think there might be a wiring issue running to the sensor. There was a very small amount of metal shavings on the old transmission speed sensor, but not enough to concern me at the present time.


I've also thought about my odometer cluster being faulty as well. I can and have the ability to swap my S10's cluster to the Blazer and see if the cluster itself is inoperable.


Any and all assistance would greatly be appreciated, thank you in advanced.

 

Transmission speed sensor is not the issue. I replaced it, did a test drive and the speedometer was still not working. With a multimeter, I tested wiring running to the speed sensor and there was voltage to be found. 3 volts to be specific. I then decided to move onto the fuse box where I took out the 10 amp fuse running the whole odometer cluster. I then swapped the fuse with a spare 10 amp fuse I had. I cranked the Blazer on, and did a test drive. This time, the speedometer was actually working. Later on during the day, I hopped into the vehicle to go take a drive. Unfortunately the speedometer was again not working. I'm almost certain now that the 10 amp fuse is the culprit. I cleaned it off with a DeoxIT spray can, air dried the fuse for about 3 minutes and set it back in. The newly cleaned fuse did not work. I did the same thing to a spare 10 amp fuse I had and the same occurrence resulted.

Anyone have any suggestions? Would love to get some help.

 

Tried some different things today. I sprayed some of the deoxidation spray into the terminal where the 10 amp fuse operates the odometer cluster. I took a lunch break and let it sit for about 4 hours before I was able to return to the Blazer. The speedometer is still not functioning. The 10 amp fuse is 100% the issue. I also unplugged both the negative and positive battery terminals to see if somehow it would reset the connection. Didn't work. I also looked at the fuse box underneath the hood of the vehicle to see if maybe there was something obstructing the fuses there. All of the fuses in the main fuse box looked about the same as the fuses that are in the cabin fuse box. The fuses I have used thus far aren't blow, they all look good. Maybe I should test the terminal with a brand new 10 amp fuse? I'm thinking the issue might be on the less accessible side of the fuse box. I'll take the cabin fuse box out and see what it looks like on the opposite end.

Any tips or tricks to get this speedometer working would be awesome.

 

Try swapping out the cluster. Not too difficult to do and would rule it out as the issue. Had the same problem with my 98 and turned out it was the cluster.

 

Apologizes for the late update. I took the weekend to enjoy my sister's college graduation.

Anyways, I swapped the S10 cluster into the Blazer. As GreenBlazer2002 stated, it was very easy to do. The S10 cluster did not fix the issue unfortunately. Everything worked minus the speedometer. Funny enough, I was having issues with my tachometer in the S10. I decided to swap the Blazer cluster into the S10 and everything works. I now know the Blazer's cluster is in perfect working condition. I'm starting to believe I have a wiring harness issue on my hands. This weekend I'll poke and prod the harness and test for continuity. Look up the schematic for the cluster harness and see where the wire is at.

Still troubleshooting! At least I fixed one issue lol!

 

Do you have a center console shifter? If a column shifter, does it display? I read on another thread, that it could be a cruise control fuse

 

I have a column shifter in the Blazer. The shifter displays as well as the mileage (the mileage just doesn't change). I inspected the cruise control fuse as well and it looked fine. The cruise control does not work when the speedometer doesn't.

 

Does the Blazer have an aftermarket radio by chance? If so you may want to double check the wiring for it. Some time in the past we had one that was wired for speed control volume and was on wrong wire or not compatible with vehicle application. Not sure, was a long time ago. Just something to check before starting a complete electrical diagnosis.
Brad

 

Yes, the Blazer does have an aftermarket radio. I don't think that the radio is affecting the speedometer. After I initially fixed it and it died again it did work twice for a couple of moments. The radio wasn't bugging out either.