Chevrolet 2008 Tahoe Owner's Manual page 112

On vehicles with a liftglass, press the button on the
underside of the license pocket applique (A) to open it.
The liftglass can also be opened by pressing the
liftglass release button on the RKE.
To open the entire liftgate, press the touchpad on the
underside of the liftgate handle (B). The vehicle must be
in PARK (P) to open the liftgate. To close the liftgate,
use the pull cup or pull strap as an aid.
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The liftgate or liftglass cannot be opened if the rear
wipers are in motion. Attempting to open the liftgate or
liftglass while the rear wipers are in motion will cause
the release of the liftglass or liftgate to delay until
the wipers are moved off the liftglass.
Both the liftglass and liftgate have an electric latch.
If the battery is disconnected or has low voltage,
the liftglass and liftgate will not open. The liftglass and
liftgate will resume operation when the battery is
reconnected and charged.
If the battery is properly connected and has adequate
voltage, and the liftgate or liftglass still will not function,
your vehicle should be taken to a dealership for service.