Hummer 2003 H2 Owner's Manual page 112

Shifting to 4HI or 4HI Lock
With the vehicle traveling less than 40 mph (64 km/h),
press and release the 4HI or 4HI Lock button.
The indicator light will flash while shifting. It will
remain illuminated when the shift is complete.
Shifting to 4LO Lock
To shift to 4LO Lock, the vehicle's engine must be
running and the vehicle must be stopped or moving
less than 2 mph (3.2 km/h) with the transmission in
NEUTRAL (N). The preferred method for shifting into
4LO Lock is to have your vehicle moving 1 or 2 mph
(1.6 to 3.2 km/h). Press and release the 4LO Lock
button. You must wait for the 4LO Lock indicator light
to stop flashing and remain illuminated before shifting
your transmission into gear.
If the 4LO Lock button is pressed when your vehicle is
in gear and/or moving, the 4LO Lock indicator light will
flash for 15 seconds and not complete the shift unless
your vehicle is moving less than 2 mph (3.2 km/h) and
the transmission is in NEUTRAL (N). After 30 seconds,
the transfer case will return to the setting last chosen.
2-30
Shifting Out of 4LO Lock
To shift from 4LO Lock to 4HI or 4HI Lock your
vehicle must be stopped or moving less than 2 mph
(3.2 km/h) with the transmission in NEUTRAL (N)
and the engine running. The preferred method for
shifting out of 4LO Lock is to have your vehicle moving
1 or 2 mph (1.6 to 3.2 km/h). Press the 4HI or 4HI Lock
button. You must wait for the 4HI or 4HI Lock indicator
light to stop flashing and remain illuminated before
shifting your transmission into gear.
If the 4HI or 4HI Lock button is pressed when your
vehicle is in gear and/or moving, the 4HI or 4HI Lock
indicator light will flash for 15 seconds but will not
complete the shift unless your vehicle is moving less
than 2 mph (3.2 km/h) with the transmission in
NEUTRAL (N).