2001 GMC Sierra 1500 Pickup Owner's Manual - Page 123

Electronic Transfer Case (If Equipped) If your four-wheel-drive vehicle has the electronic transfer case, the transfer case switches are located to the left of the instrument panel cluster. Use these switches to shift into and out of four-wheel drive. You can choose among three driving settings: 2HI: This setting is for driving in most street and highway situations. Your front axle is not engaged in two-wheel drive. 4HI: This setting engages your front axle to help drive your vehicle. Use 4HI when you need extra traction, such as on snowy or icy roads, or in most off-road situations. 4LO: This setting also engages your front axle to give you extra traction. You may never need 4LO. It sends the maximum power to all four wheels. You might choose 4LO if you were driving off-road in sand, mud or deep snow and climbing or descending steep hills. Indicator lights in the switches show you which setting you are in. The indicator lights will come on briefly when you turn on the ignition and the last chosen setting will stay on. If the lights do not come on, you should take your vehicle in for service. An indicator light will flash while shifting. It will remain illuminated when the shift is completed. If for some reason the transfer cannot make a requested shift, it will return to the last chosen setting. 2-40