2006 GMC Sierra 1500 Pickup Owner's Manual - Page 138

Shifting into Four-Wheel High or AUTO 4WD (Automatic Four-Wheel Drive) Press and release the four-wheel high or AUTO 4WD switch. This can be done at any speed, except when shifting from Four-Wheel Low, and the indicator light will flash while shifting. It will remain on when the shift is completed. Shifting into Two-Wheel High Press and release the Two-Wheel High switch. This can be done at any speed, except when shifting from Four-Wheel Low. To shift to Four-Wheel Low, the ignition must be in RUN and the vehicle must be stopped or moving less than 3 mph (5 km/h) with the transmission in NEUTRAL (N). The preferred method for shifting into Four-Wheel Low is to have your vehicle moving 1 to 2 mph (1.6 to 3.2 km/h). Press and release the Four-Wheel Low switch. You must wait for the Four-Wheel Low indicator light to stop flashing and remain on before shifting your transmission in gear. Notice: Shifting the transmission into gear before the Four-Wheel Low indicator light has stopped flashing could damage the transfer case. To help avoid damaging your vehicle, always wait for the Four-Wheel Low indicator light to stop flashing before shifting the transmission into gear. It is typical for your vehicle to exhibit significant engagement noise and bump when shifting between Four-Wheel Low and Four-Wheel High ranges or from NEUTRAL (N) with the engine running. If the Four-Wheel Low switch is pressed when your vehicle is in gear and/or moving, the Four-Wheel Low indicator light will flash for 30 seconds and not complete the shift unless your vehicle is moving less than 3 mph (5 km/h) and the transmission is in NEUTRAL (N). After 30 seconds the transfer case will shift to four-wheel high mode. Shifting into Four-Wheel Low Notice: Shifting the transfer case into Four-Wheel Low while moving at speeds faster than 3 mph (5 km/h) may cause premature wear to the transfer case, and may cause the gears to grind. To avoid causing premature wear, and grinding the gears, do not shift the transfer case into Four-Wheel Low while the vehicle is moving faster than 3 mph (5 km/h). 2-44