2003 GMC Envoy Owner's Manual - Page 343

Rear Axle When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. To get an accurate reading, the vehicle should be on a level surface. The proper level is from 0 to 3/8 inch (0 to 10 mm) below 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 6-17 How to Check Lubricant 5-48