Speedometer Stepper Motors

If stepper loses a step or more, MCU has no way to tell, so the error becomes "permanent" untill the next restart-calibration. If for some reason stepper stops and restarts, the position error would be mostly random. Having correct speed after dead stop is higly impropable. If this happens it's a sign that MCU for some reason was reset (possible powering problem) or just CW lost steps were more than CCW ones, so it calibrated by mistake. That's some clue to detect if the stepper is at fault. If yes I would first verify it moves freely. If it does, problem could be just a bad electrical connection or solder point typical for the Pb-free solder. Trying to replace stepper would be my last resort. S.M.

In order to tell that the speedo works above 80mph, you must have gotten this Hummer up to that speed...glad I wasn't there on the same road.

You just an't right, At 0 mph (stoped) the speedo was reading 80mph, my Hummer was not moving. I hope you got it now.

Is it possible that the pointer has slipped on the shaft? Repositioning the pointer is a simpler and cheaper fix than replacing parts.

Hi, GM used bad instrument cluster motors in all 2003-2006 SUVs, trucks, and in half of the cars they sold. It was not recalled as it was not considered a safety feature and the US gov agreed. Eventually all 7 motors (Gas gauge, pressure, temp, etc) will go. New Cluster sold by GM for 400+ or you can get repaired from $100 to $150. If you remove yourself and send away you can get for 90 plus shipping. No wonder GM is going under. There are currently 40+ flaky parts on GM model SUVs and Trucks 2000 to 2006 that tend to oddly go just after warranty is up. There are several companies that can repair the cluster and some just do an exchange and the vehicle can be driven without the cluster while it is out being repaired just do a google search for hummer speedometer repair or if you live in a larger metro area then you can look for a speedometer repair facility which can repair your dash for a lot less than a dealer.

Internet auction sites (name withheld) are ideal for solving problems like this. Get rid of it.