Opening the Rear Compartment Without Electrical Power

WARNING: This page is about a different car, the 2019 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.

Open the rear door.
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Using the appropriate trim tool (1), insert the tool in between the rear window panel trim and the rear seat back cushion to locate the rear seat latch (2). The latch should be below the seat belt.
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Once locating the cable in the opening in the latch (2), move the handle of the trim tool (1) to the right which will move the release cable to the left and release the rear seat back cushion.
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Using the trim tool (1), locate the cable collar/slug in the latch (2) to release the rear seat back.
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NOTE:
Make sure the auxiliary rear compartment latch release handle and cable are fully seated, if not this will cause the rear compartment release switch to be inoperable.

Once the rear seat back is open, reach in and pull the auxiliary rear compartment latch release handle (1).