GMC 2009 Yukon XL Owner's Manual page 122

Obstacle Detection Features
If the liftgate encounters an obstacle during a power
open or close cycle, a warning chime will sound and the
liftgate will automatically reverse direction to the full
closed or open position. After removing the obstruction,
the power liftgate operation can be used again. If the
liftgate encounters multiple obstacles on the same power
cycle, the power function will deactivate, and you
must manually open or close the liftgate. The REAR
ACCESS OPEN warning message in the Driver
Information Center (DIC) will indicate that the liftgate is
open. After removing the obstructions, manually
open the liftgate to the full open position or close the
liftgate to the fully closed and latched position. The
liftgate will now resume normal power operation.
Your vehicle has pinch sensors located on the side
edges of the liftgate. If an object is caught between the
liftgate and the body and presses against this sensor,
the liftgate will reverse direction and open fully.
The liftgate will remain open until it is activated again or
closed manually. Do not force the liftgate open or
closed during a power cycle.
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Manual Operation of Power Liftgate
To change the liftgate to manual operation, press the
switch on the overhead console to the OFF position.
With the power liftgate disabled and all of the doors
unlocked, the liftgate can be manually opened and
closed.
To open the liftgate, press the touchpad on the handle
on the outside of the liftgate, and lift the gate open.
To close the liftgate, use the pull cup to lower the liftgate
and close. The liftgate latch will power close. Always
close the liftgate before driving.
If the RKE button or the power close button on the liftgate
is pressed while power operation is disabled, the lights
will flash three times, but the liftgate will not move.
It is not recommended that you drive with the liftgate
open, however, if you must drive with the liftgate open,
the liftgate should be set to manual operation by pressing
the OFF switch on the center console.
The liftgate has an electric latch. If the battery is
disconnected or has low voltage, the liftgate will not open.
The liftgate will resume operation when the battery is
reconnected and charged.
If the battery is properly connected with adequate
voltage, the switch is not disabled, and the liftgate still will
not function, your vehicle should be taken to a dealer/
retailer for service.