If your vehicle is showing power folding mirrors won't fold or unfold, here are the most likely causes and the parts you'll need to fix each one.
The fuse protecting the mirror circuit can blow if the mirrors are frozen shut with ice or manually forced, which overloads the folding motor.
The control switch on the door panel is exposed to rain, snow, and dirt when the window is down, causing the internal electrical contacts to corrode or fail.
The small electric motor or plastic gears inside the mirror housing can strip or burn out over time, especially if the mirror is frequently forced open or closed by hand.
If the door panel was recently removed for window or speaker repairs, the electrical connector for the mirror switch or the mirror itself may not have been fully plugged back in.
The wiring harness passing through the rubber boot between the car body and the door bends every time the door opens, which can eventually cause the wires to fray and break.
The computer that controls body functions may have a software glitch or internal hardware failure preventing it from sending the fold/unfold command to the mirrors.