Rear Hatch/Gate Description and Operation General
The lift glass can be opened by any of the following components:
Lift gate window release switch
Door lock cylinder switch
Keyless entry transmitter
When the lift gate window release switch is operated ground is applied to the body control module (BCM) and a lift glass release output is sent to the lift glass relay. An open output can also be commanded by the BCM when an open input is received from the remote control door lock receiver. When the BCM grounds the relay with a commanded open the lift glass relay coil energizes and the switch side of the relay closes. Battery voltage is then applied directly to the lift gate window release actuator. This will release the lift glass. The lift gate window release actuator can also be energized when the lift gate lock cylinder switch is operated.
Try pulling the lift glass relay from the under hood fuse box. If the glass will latch, this relay is stuck in the closed position or the input wire going to the body control module is grounded.
The relay is a long shot, as most relays quit in the open position, but it might be your problem and is the easiest to check.
Next step would be to remove the interior trim pieces and inspect the latch.