Speedometer

Simple, reliable, common sense speedometer cables apparently don't work anymore. Now we have complicated computers. An inoperative speedometer can be caused by the Engine Computer, Transmission Computer, Body Computer, or the instrument cluster which is also a computer module. You can't even pop in used computers from the salvage yard as a test because new ones have to be programmed to the specific car by the dealer. GM is the only manufacturer that does not allow independent shops to do that. They have a lot of business practices like that to make them money after the sale.

My best recommendation is to let the dealer handle this problem. If you knew for sure the problem was in the instrument cluster, you could do an internet search for places that repair GM clusters. There are a lot of them.