GMC 2004 Yukon XL Owner's Manual page 124

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 3-56.
Shifting into 4HI or AUTO 4WD
Press and release the 4HI or AUTO 4WD button.
This can be done at any speed (except when shifting
from 4LO), and the indicator light will flash while shifting.
It will remain illuminated when the shift is completed.
Shifting into 2HI
Press and release the 2HI button. This can be done at
any speed (except when shifting from 4LO).
Shifting into 4LO
To shift to the 4LO position, the ignition must be in RUN
and the vehicle must be stopped or moving less than
3 mph (4.8 km/h) with the transmission in NEUTRAL (N).
The preferred method for shifting into 4LO is to have
your vehicle moving 1 to 2 mph (1.6 to 3.2 km/h). Press
and release the 4LO button. You must wait for the
4LO indicator light to stop flashing and remain
illuminated before shifting your transmission in gear.
2-30
Notice: Shifting the transmission into gear before
the 4LO indicator light has stopped flashing
could damage the transfer case. To help avoid
damaging your vehicle, always wait for the 4LO
indicator light to stop flashing before shifting
the transmission into gear.
It is typical for your vehicle to exhibit significant
engagment noise and bump when shifting between
4LO and 4HI ranges or from NEUTRAL with the
engine running.
If the 4LO button is pressed when your vehicle is in
gear and/or moving, the 4LO indicator light will flash for
30 seconds and not complete the shift unless your
vehicle is moving less than 3 mph (4.8 km/h) and the
transmission is in NEUTRAL (N). After 30 seconds
the transfer case will shift to 4HI mode.