Got a text from my buddy's mom this morning asking if I might be able to fix the speedometer on her late husband's truck they are getting ready to sell. The truck is I think an 03 or 04 Silverado 2500 Duramax (same one I posted a thread on about a month ago trying to put a value on it.) My research abilities are limited at the moment, as I am at work currently and our network blocks access to most forums (thankfully GRM makes it through unscathed, but don't tell anyone 
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As far as I recall, the odometer still works, the speedo just sits at zero most of the time, with very intermittent spurts of actually working. I'd really like to help her out with the repair if it is something simple enough, however I don't think I would be too keen on pulling the whole dash apart chasing random electrical gremlins on someone else's truck they're getting ready to sell. Thoughts from the hive?
There's little servo motors on those dashes that go bad. Speedo is usually one of the first. You can google how to solder your own replacements in or it's ~$150 to have the whole cluster redone.
So looking around it seems its either a Cluster issue or the stepper motor in the cluster. Here are the instructions from the interwebs for when you can see them. http://www.instructables.com/id/DIY-Finally-How-To-Repair-a-GM-Instrument-Cluster-/?ALLSTEPS
It involves desoldering the old stepper motor and replacing it.
The system consists of a speed sensor, the pcm, the gauge, and wiring. If you have a way to scan it while driving do that. If the scan tool shows your speed you know that the sensor and pcm are doing their job. If you can't do that then take it out for a drive, if the trans shifts properly then the sensor and pcm are most likely fine because the computer uses the speed sensor to know when to shift. If it doesn't shift correctly it is not a gauge problem.
One of the important things to be sure of is whether the odo works when the speedo does not. That knowledge breaks the problem down to in the cluster, or outside the cluster.
And stepper motors are a common failure point.
Seems to be something within the cluster, stepper motor most likely, odo and trans were functioning fine when I was last in the truck about a month ago.
Doesn't look too hard to replace the stepper motors, but I guess she called the dealer at some point today, who seems to think the issue may be covered under some type of recall. So looks like they're gonna take a crack at it and hopefully fix it for free, and if not it doesn't sound too bad for yours truly to handle. Thanks guys!
