GMC Sierra Classic 2007 Owner's Manual page 165

If the Four-Wheel Drive Low switch is pressed
when your vehicle is in gear and/or moving,
the Four-Wheel Drive Low indicator light will flash
for 30 seconds and not complete the shift
unless your vehicle is moving slower than 3 mph
(5 km/h) and the transmission is in NEUTRAL (N).
The transfer case will shift to Four-Wheel Drive
High while waiting to complete the shift.
It is normal to hear and feel your vehicle's transfer
case shift into Four-Wheel Drive Low. If you shift
with the vehicle stopped, the indicator light may
continue to flash slowly. It may be necessary to shift
the transmission momentarily into REVERSE (R)
and DRIVE (D), for an automatic transmission, or
REVERSE (R) and FIRST (1) for a manual
transmission to make the light stop flashing.
Shifting from Four-Wheel Drive Low to
Four-Wheel Drive High or Two-Wheel
Drive High
To shift from Four-Wheel Drive Low to Four-Wheel
Drive High or Two-Wheel Drive High, your
vehicle must be stopped or moving less than
3 mph (5 km/h) with the transmission in
NEUTRAL (N) for an automatic transmission or
the clutch pedal pressed for a manual
transmission. The preferred method for shifting out
of Four-Wheel Drive Low is to have your vehicle
moving 3 mph (5 km/h).
Press and release the Two-Wheel Drive High or
Four-Wheel Drive High switch. You must wait
for the Two-Wheel Drive High or Four-Wheel Drive
High indicator light to stop flashing and stay on
before shifting the transmission into gear or
releasing the clutch pedal.
If the Four-Wheel Drive High switch is pressed
when your vehicle is in gear, the Four-Wheel Drive
High indicator light will flash for 30 seconds but
the vehicle will not complete the shift unless
it is moving slower than 3 mph (5 km/h) and the
transmission is in NEUTRAL (N).
165