2004 GMC Sonoma Owner's Manual - Page 290

Rear Axle When to Check and Change Lubricant It is not necessary to regularly check rear axle fluid unless you suspect there is a leak or you hear an unusual noise. A fluid loss could indicate a problem. Have it inspected and repaired. Refer to the Maintenance Schedule to determine how often to check the lubricant and when to change it. See Part A: Scheduled Maintenance Services on page 6-4. 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. 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. How to Check Lubricant Four-Wheel Drive Lubricant checks in this section also apply to these vehicles. However, there are two additonal systems that need lubrication. Transfer Case When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. See Part C: Periodic Maintenance Inspections on page 6-30. 5-46