What could be the reason that the USB port in my GMC Acadia is not functioning properly?

The reason why the USB port in the GMC Acadia is not working is likely because of a faulty fuse in the fuse box. To access the fuse box, locate a small seam or crack along the dashboard to the left of the steering wheel. Use a screwdriver or prybar to open the panel. Inside, you will see a variety of fuses. On the back of the panel you opened, there should be a diagram indicating the purpose of each fuse. If the diagram is not there, you can refer to the vehicle's owner's manual. Once you determine which fuse needs to be replaced, remove it. Check if the thin strip of metal connecting the two raised sections on the fuse is intact. If it is broken, the fuse is faulty and needs to be replaced. If the strip is intact, the fuse is still good and can be reinserted. New fuses are relatively inexpensive, costing around $10.