GMC 2007 Acadia Owner's Manual page 112

Power Liftgate Button Near Liftgate Latch
The liftgate can also be closed by pressing the
power liftgate button next to the liftgate latch. Press
the button a second time during liftgate operation to
reverse that operation.
The power liftgate may be temporarily disabled
under extreme temperatures, or under low battery
conditions. If this occurs, the liftgate can still be
operated manually.
If you shift the transmission out of PARK (P) while
the power function is in progress, the liftgate power
function will continue to completion. If you shift the
transmission out of PARK (P) and accelerate before
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the power liftgate latches closed, the liftgate may
reverse to the open position. Cargo could fall out of
the vehicle. Always make sure the power liftgate is
closed and latched before you drive away.
If you power open the liftgate and the liftgate
support struts have lost pressure, the lights will
flash and a chime will sound. The liftgate will stay
open temporarily, then slowly close. See your
dealer/retailer for service before using the liftgate.
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 LIFTGATE 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.