GMC 2008 Envoy Denali Owner's Manual page 106

Shifting into NEUTRAL
Before shifting the transfer case to NEUTRAL, first
make sure the vehicle is parked so that it will not roll.
1. Set the parking brake.
2. Start the vehicle.
3. Put the transmission in NEUTRAL (N).
4. Shift the transfer case to Two-Wheel High.
5. Turn the transfer case knob all of the way past
Four-Wheel Low and hold it there for a minimum of
10 seconds. The neutral indicator light will come on.
6. With the engine running, shift the transmission to
REVERSE (R) for one second, then shift the
transmission to DRIVE (D) for one second, to
ensure that the transfer case is in NEUTRAL.
7. Turn the engine off, by turning the key to
ACC/ACCESSORY.
8. Place the transmission shift lever in PARK (P).
9. Turn the ignition to LOCK/OFF.
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Shifting Out of NEUTRAL
To shift the transfer case out of NEUTRAL, do the
following:
1. Set the parking brake and apply the regular brake
pedal.
2. Turn the ignition to ON/RUN with the engine off.
3. Put the transmission in NEUTRAL (N).
4. Turn the transfer case knob to the desired position
(Two-Wheel High, Four-Wheel High, or Auto
Four-Wheel Drive).
5. After the transfer case has shifted out of NEUTRAL,
the indicator light will go out.
6. Release the parking brake.
7. Start the engine and shift the transmission to the
desired position.