Circuit/System Verification
WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
Ignition ON, observe the scan tool Mirror Horizontal Position and Mirror Vertical Position parameters. The reading should be between 0.2-4.8 volts and change as the mirror is moved, left, right, up, and down.