Pontiac 2005 Montana Owner's Manual page 120

To close the liftgate, pull down on the handle, then
firmly shut the liftgate. Don't drive with the liftgate open,
even slightly. See Engine Exhaust on page 2-40 .
A message in your instrument panel cluster will warn
you if the liftgate is not completely closed. See
Rear Hatch Ajar Warning Message on page 3-50 .
2-22