2001 GMC Yukon Owner's Manual - Page 104

4HI: Use 4HI when you need extra traction, such as on snowy or icy roads or in most off-road situations. This setting also engages your front axle to help drive your vehicle. This is the best setting to use when plowing snow. 4LO: This setting also engages your front axle and delivers extra torque. You may never need 4LO. It sends maximum power to all four wheels. You might choose 4LO if you are driving off-road in deep sand, deep mud, deep snow and climbing or descending steep hills. Indicator lights in the switches show which setting you are in. The indicator lights will come on briefly when you turn on the ignition and one will stay on. If the lights do not come on, you should take your vehicle to your dealer for service. An indicator light will flash while shifting the transfer case. It will remain illuminated when the shift is complete. If for some reason the transfer case cannot make a requested shift, it will return to the last chosen setting. If the SERVICE 4WD light stays on, you should take your vehicle to your dealer for service. See "Service 4WD" in the Index for further information. Shifting to 4HI or AUTO 4WD Press and release the 4HI or AUTO 4WD switch. This can be done at any speed (except when shifting from 4LO), and the indicator light will flash while shifting. It will remain illuminated when the shift is completed. Shifting to 2HI Press and release the 2HI switch. This can be done at any speed (except when shifting from 4LO). CAUTION: Shifting the transfer case to NEUTRAL can cause your vehicle to roll even if the transmission is in PARK (P). You or someone else could be seriously injured. Be sure to set the parking brake before placing the transfer case in NEUTRAL. See "Parking Brake" in the Index. NEUTRAL: Shift the vehicle's transfer case to NEUTRAL only when towing your vehicle. See "Recreational Vehicle Towing" or "Towing Your Vehicle" in the Index for more information. 2-26