My 99 is giving me a hard time! A few months ago, I started having problems with my speedometer going out. It would show the speed, then flop over to zero, then pop back. I didn't drive it much then, so it was no big deal. But now I've had to put my other truck up to work on it, and it is driving me crazy! I replaced the rear speed sensor (it's a manual, so I only have one), and got no change. I inspected the harness from the frame to the axle, and nothing was bad. I cleaned the harness coupling by the driver side front tire, but still I had problems. By this time, it had gotten worse. Now, it jumps around wildly, pegging out at buth ends periodically. Then I tried unplugging and cleaning the data bus that feeds from the PDC. Finally, I even unplugged the sensor, tied up the harness, and drove it like that. The needle still jumped!! It always seems to coincide with a bump in the road. For a while, I could alleviate the symptoms by running off the road a little. This would jar it into working again for a while. I noticed after jumpstarting a backhoe, my brother shut the hood and the needle jumped. I had him do it again, and the needle jumped again. I will not pretend this thing has never seen mud, and just a short while ago my relays went bad, apparenty due to off-roading. Any thoughts?? Thanks!!

 

You have a bad connection somewhere. Trace all wires responsible for speedo, clean all connections. See if that doesn't help.

 

What haven't I checked? The only thing I can imagine is the PCM it's self... And whats the best thing to use to clean and prevent?

 

PCM gets its signal from the sensor, and then tells the cluster what speed to read.... (via the CTM I think). Not exactly the best design in the world...... There is just a boatload of 'stuff' between the sensor, and the speedo.

 

Can you reccomend a method to clean the connectors? I tried electrical parts cleaner and dielectric grease...

 

I use brake cleaner, and a tiny little wire brush....... I have no idea where the brush came from......

 

Alright, I think I fixed it. I pulled the battery, then removed the PCM connectors. I sprayed them with contact cleaner, replaced them, removed them again, sprayed again and coated the sockets with dielectric grease. It worked all day!! Thanks!!

 

Thanks!!

 

Awesome! Glad ya got it working.