GMC 2003 Yukon Owner's Manual page 123

Shifting into 4LO
To shift to the 4 lo 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 4 lo switch. You must wait for the
4LO indicator light to stop flashing and remain
illuminated before shifting your transmission in gear.
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 4 lo switch 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 return to the setting last chosen.
Shifting Out of 4LO
To shift from 4LO to 4HI, AUTO 4WD or 2HI your
vehicle must be stopped or moving less than 3 mph
(4.8 km/h) with the transmission in NEUTRAL (N) and
the ignition in RUN. The preferred method for shifting out
of 4LO is to have your vehicle moving 1 to 2 mph
(1.6 to 3.2 km/h). Press and release the 4HI,
AUTO 4WD or 2HI switch. You must wait for the 4HI,
AUTO 4WD or 2HI indicator light to stop flashing
and remain illuminated before shifting your transmission
into gear.
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 4HI, AUTO 4WD or 2HI switch is pressed when
your vehicle is in gear and/or moving, the 4HI,
AUTO 4WD or 2HI indicator light will flash for
30 seconds but will not complete the shift unless your
vehicle is moving less than 3 mph (4.8 km/h) and
the transmission is in NEUTRAL (N).
2-29