Thanks, XXXXX XXXXX I needed. That makes it an end gate. It sounds like the linkage has become unhooked from the actuator to the latch. Not uncommon. Once it is fixed, safety wire it so it can't happen again. On some of them you can pull the top of the trim panel upward and back far enough to access and trip the latch mechanism with a long thin screw driver. If that doesn't work for you it gets harder. If you can't access it from between the window and gate by pulling the top of the panel upward and back for room then you are going to need to remove the inner trim panel. It may be that there will be some breakage of the panel because of hidden screws that go into the sides of the end gate to hold the trim in place. Those would be my only concern. But if you work at it and take your time you may be able to work the panel off. Just remember that the panel slides upward to remove, it does not pull toward you. It has plastic fingers that slide into the metal skin of the door. About the best I can do for you is send you the removal instructions from the GM service manual for the trim and hope you can manage to get it off so you can inspect the linkage. Good luck with it and thanks, Bob
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Tighten Tighten the screws to 1.9 N·m (17 lb in).
Tighten Tighten the screw to 1.9 N·m (17 lb in).
Tighten Tighten the handle to 2.8 N·m (25 lb in).