2004 GMC Yukon Owner's Manual - Page 434

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. Bulb Replacement For any bulb changing procedure not listed in this section, contact your dealer. See Replacement Bulbs on page 5-62 for the proper types of bulbs to use. What to Use To determine what kind of lubricant to use, see Recommended Fluids and Lubricants on page 6-14. Halogen Bulbs {CAUTION: Halogen bulbs have pressurized gas inside and can burst if you drop or scratch the bulb. You or others could be injured. Be sure to read and follow the instructions on the bulb package. 5-56