2002 GMC Yukon Owner's Manual - Page 350

How to Check Lubricant What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See "Recommended Fluids and Lubricants" in the Index. Front Axle When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. See "Scheduled Maintenance Services" in the Index. Automatic Transfer Case To get an accurate reading, the vehicle should be on a level surface. If the level is below the bottom of the filler plug hole, you'll need to add some lubricant. Add enough lubricant to raise the level to the bottom of the filler plug hole. Use care not to overtighten the plug. 6-29