Hummer 2007 H2 Owner's Manual page 130

Indicator lights in the buttons show which mode you
are in. The indicator lights will come on briefly when
you turn on the ignition and one will stay on. If the
lights do not come on, you should take your vehicle
to your dealer for service. An indicator light will flash
while shifting the transfer case. It will remain on
when the shift is complete. If for some reason the
transfer case cannot make a requested shift, it will
return to the last chosen setting.
If the SERVICE 4WD message stays on, you
should take your vehicle to your dealer for service.
See "Service 4WD message" under Driver
Information Center (DIC) on page 222.
Shifting between Four-Wheel High and
Four-Wheel-High Lock
With the vehicle traveling less than 40 mph
(64 km/h), press and release the Four-Wheel High
or Four-Wheel-Low Lock button. The indicator
light will flash while shifting. It will remain on when
the shift is complete.
It may be necessary to drive backwards for a
short distance of 25 feet (7.5 m) to get the lock
feature to disengage.
130
Shifting into Four-Wheel-Low Lock
To shift into Four-Wheel-Low Lock, the ignition
must be in RUN and the vehicle must be stopped or
moving less than 3 mph (5 km/h) with the
transmission in NEUTRAL (N). The preferred
method for shifting into Four-Wheel Low is to have
your vehicle moving 1 to 2 mph (1.6 to 3.2 km/h).
Press and release the Four-Wheel-Low Lock
button. You must wait for the Four-Wheel-Low Lock
indicator light to stop flashing and remain lit before
shifting your transmission in gear.
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.
It is normal for your vehicle to have engagement
noise and bump when shifting between
Four-Wheel Low and Four-Wheel High or
Four-Wheel-High Lock ranges or from NEUTRAL
with the engine running.