before buying a motor, remove the plastic from the hatch and get at the wing. Apply 12v dc directly to that motor and see if it's bad: look at the rotating gear and inspect the cut on/off switch. Remove the rubber boot at the top of the hatch and inspect the wire for a break. While you are there and at final reassembly be sure to reseal the wing plate with "MoreTite" or similar sealing caulk.
There may be a problem with the Body Control Module (BCM), wheel speed sensors, or the ESP/BAS module which may or may not set a warning light. Getting a diagnostic scan from an appropriate tool that gets beyond just OBD codes will get you headed in the right direction.