GMC 2007 Yukon XL Owner's Manual page 124

To unlock the liftgate, use the power door lock
switch or press the door unlock button on
the Remote Keyless Entry (RKE) transmitter twice.
See Remote Keyless Entry System Operation
on page 113.
To open the liftglass, press the button on the
underside of the license pocket applique (A).
The liftglass can also be opened by pressing the
liftglass release button on the RKE.
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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.
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.