2004 GMC Sonoma Owner's Manual - Page 292

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 1/2 inch (12 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 See Replacement Bulbs on page 5-54 for the proper types of bulbs to use. For any bulb changing procedure not listed in this section, contact your GM dealer's service department. Halogen Bulbs 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 6-32. {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. 5-48