2007 GMC Yukon Owner's Manual - Page 149

It is typical for your vehicle to exhibit significant engagement noise and bump when shifting between Four-Wheel Drive Low and Four-Wheel Drive High ranges or from NEUTRAL with the engine running. If the knob is turned to the Four-Wheel Low position 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 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 Drive High mode. You must wait for the Four-Wheel Drive High, AUTO or Two-Wheel Drive High indicator light to stop flashing and remain on before shifting your transmission into 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 Drive Low and Four-Wheel Drive High ranges or from NEUTRAL with the engine 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 Out of Four-Wheel Drive Low To shift from Four-Wheel Drive Low to Four-Wheel Drive High, AUTO 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) and the ignition in RUN. The preferred method for shifting out of Four-Wheel Drive Low is to have your vehicle moving 1 to 2 mph (1.6 to 3.2 km/h). Turn the knob to the Four-Wheel Drive High, AUTO or Two-Wheel Drive High position. 149