2003 GMC Yukon Owner's Manual - Page 410

Front Axle When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. See Part A: Scheduled Maintenance Services on page 6-4. If the level is below the bottom of the filler plug hole, you may need to add some lubricant. When the differential is cold, add enough lubricant to raise the level to 0 to 3/8 inch (9.5 mm) below the filler plug hole. When the differential is at operating temperature (warm), add enough lubricant to raise the level to the bottom of the filler plug hole. How to Check Lubricant What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See Part D: Recommended Fluids and Lubricants on page 6-17. Bulb Replacement For any bulb changing procedure not listed in this section, contact your dealer. See Replacement Bulbs on page 5-59 for the proper types of bulbs to use. To get an accurate reading, the vehicle should be on a level surface. 5-52