Hummer H2 2009 Owner's Manual page 126

If the Four-Wheel-Low Lock position is selected when
the vehicle is in gear and/or moving, the Four-Wheel
Low Lock indicator light will flash for 15 seconds and
not complete the shift unless the vehicle is moving
less than 3 mph (5 km/h) and the transmission is
in N (Neutral). After 15 seconds the transfer case
will return to the setting last chosen.
Shifting Out of Four-Wheel Low Lock
To shift from Four-Wheel-Low Lock to Full-Time
Four-Wheel Drive or Four-Wheel-High Lock, the vehicle
must be stopped or moving less than 3 mph (5 km/h)
with the transmission in N (Neutral) and the ignition in
ON/RUN. The preferred method for shifting out of
Four-Wheel-Low Lock is to have the vehicle moving
1 to 2 mph (1.6 to 3.2 km/h). Turn the dial to the
Full-Time Four-Wheel Drive or Four-Wheel-High Lock
position. You must wait for the Full-Time Four-Wheel
Drive or Four-Wheel-High Lock indicator light to stop
flashing and remain lit before shifting the transmission
into gear.
2-40
It is normal for the vehicle to have engagement noise
and bump when shifting between Four-Wheel Low Lock,
Full-Time Four-Wheel Drive or Four-Wheel-High Lock
ranges or from N (Neutral) with the engine running.
If the Full-Time Four-Wheel Drive or
Four-Wheel-High Lock position is selected when
the vehicle is in gear and/or moving, the Full-Time
Four-Wheel Drive or Four-Wheel-High Lock indicator
light will flash for 30 seconds but will not complete
the shift unless the vehicle is moving less than 3 mph
(5 km/h) and the transmission is in N (Neutral).
Notice: Shifting the transmission into gear before
the indicator light stops flashing could cause
damage to the transfer case. Always wait until the
indicator light stops flashing before putting the
transmission back in gear.