GMC Yukon 2007 Owner's Manual page 158

The vehicle may have significant engagement
noise and bump when shifting between
Four-Wheel Drive Low and Four-Wheel Drive
High ranges or from NEUTRAL while the engine
is running.
If the knob is turned to the Four-Wheel Drive High,
AUTO, or Two-Wheel Drive High switch position
when your vehicle is in gear and/or moving,
the Four-Wheel Drive High, AUTO or Two-Wheel
Drive High indicator light will flash for 30 seconds
but will not complete the shift unless your
vehicle is moving less than 3 mph (5 km/h) and
the transmission is in NEUTRAL (N).
Shifting into NEUTRAL
To shift the transfer case to NEUTRAL do the
following:
1. Make sure the vehicle is parked so that it will
not roll.
2. Set the parking brake and apply the regular
brake pedal. See Parking Brake on page 160
for more information.
3. Start the vehicle or turn the ignition to RUN.
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4. Put the transmission in NEUTRAL (N).
5. Shift the transfer case to Two-Wheel
Drive High.
6. Turn the transfer case dial clockwise to
NEUTRAL till it stops and hold it for
10 seconds. Then slowly release the dial to
the four low position. The NEUTRAL light will
come on when the transfer case shift to
NEUTRAL is complete.
7. If the engine is running, verify that the
transmission is in NEUTRAL (N) by shifting the
transmission to REVERSE (R) for one second,
then shift the transmission to DRIVE (D) for
one second.
8. Turn the ignition to ACCESSORY, which will
turn the engine off.
9. Place the transmission shift lever in PARK (P).
10. Release the parking brake prior to moving
the vehicle.
11. Turn the ignition to LOCK.