GMC 2009 Yukon XL Owner's Manual page 119

If your vehicle has a power liftgate, see Power Liftgate
on page 2-14.
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 (RKE) System Operation on page 2-5.
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.
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.
2-13