I am about at wits end with the randomly working speedometer in my 95 GC. I have been through 2 complete gauge cluster, 3 different circuit boards that go on the back of the speedometer itself, 2 transmission speed sensors, and I have cleaned the grounds that attach to the engine block and fender. When the speedometer works, it works great, and the odometer spins as it should. Then for no reason, it will die completely and take the odometer with it. This seems to happen upon the first time the vehicle is started or restarted. After I drive for about 5 or 10 minutes, it will usually come back on and stay on until the vehicle is restarted again. Temperature does not seem to matter as this has happened in cold, warm, and hot weather. For ****s and giggles, I have tried the cruise control when the speedo dies, and it functions normally.
The way this happens leads me to believe it is some sort of ground issue, but I haven't found any obvious issues. Do any of you have any other suggestions I could try? Could it be the pcm having issues?
Sure have, my 95 Orvis speedometer would just give up randomly too, it register fine and then drop to 0 randomly. I also changed the speedometer head unit and the speed sensor but the problem still there, I gave up on it lol.
If it were a ground issue with the instrument cluster, then it should affect other gauges as well I would think. Regardless, the ground for the instrument cluster is located at the left kick panel. You can check it and see if that is the problem.
More likely, you have an electrical signal problem between your Vehicle Speed Sensor (VSS) and your speedometer/odometer. I'm looking at a wiring diagram that I believe applies to your model. The feed off of the VSS is an 18 gauge orange/white wire that runs to a splice, and the splice branches the signal to the Powertrain Control Module, the Transmission Control Module, the VIC (if equipped), and the Instrument Cluster. I believe the splice may be near the injectors (it is labeled "INJ"). The potential problems are (a) in that 20 gauge wire between the splice and the instrument cluster, (b) the connector to the splice, (c) the terminal connection to the instrument cluster, or (d) the connector at the instrument cluster. Inspect the splice and terminal connections to solve (b) and (c). Put some dielectric grease on the instrument panel connector to solve (d). You would just need to run another wire to solve (a).
If indeed that splice is near the injectors, it would make the most sense that vibration from the engine is causing erratic disconnects.
Well, I don't have the VIC, so that removes one possible issue, lol. I'll check under the hood tonight and see if I can find the splice. Never even thought about the dielectric grease on the instrument cluster connector. It's just weird how it randomly happens, even on smooth road.
Just a little update... I was finally able to get around to taking the dash back apart this past weekend. I dielectric greased the mess out of the speedo circuit board where it connects to to the speedo head and the cluster plug itself. Long story short, it still is acting the same way. I really hate digging into the wiring harness considering its all located at the back of the valve cover with very little room to work. I would hate messing up another wire for something trying to remove the wire loom cover. This freakin sucks .
I have been through 2 complete gauge cluster, 3 different circuit boards that go on the back of the speedometer itself, 2 transmission speed sensors, and I have cleaned the grounds that attach to the engine block and fender.
I have been troubleshooting the exact same problem in my '98 since April now. I have spent countless hours with the dash apart, as well as a few of my mechanic friends. I am at absolute wits end also. I have given up as it was stressing me out. Im eventually gonna bring it to a real shop and leave it until they figure it out, but since its not my daily driver there isnt much of a rush....its runs lol
__________________ 1998 5.9 Limited
• AEM BruteForce Intake • Mopar M1 Intake Manifold •BBK 52MM Throttle Body •Carsound Cat •Flowmaster Super 44 • Pro-Comp MX-6 Shocks Custom SCT Tuned by Sean Powell "HEMIFEVER"
Yeah, vehicle speed sensor. I had transmission on the brain since it came out of the tailshaft of the tranny, lol. I really don't want to take it to a shop... they would end up replacing the same things more than likely and run up an unpleasant bill. I originally bought it to fix up and sell, so any more repair bills would put me over budget, especially for exploratory work.