2008 GMC Envoy Owner's Manual - Page 341

How to Check Lubricant Four-Wheel Drive Transfer Case When to Check Lubricant It is not necessary to regularly check 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. How to Check Lubricant To get an accurate reading, the vehicle should be on a level surface. To get an accurate reading, the vehicle should be on a level surface. The proper level is from 0 to 0.40 inch (0 to 10 mm) below the bottom of the filler plug hole, located on the rear axle. What to Use To determine what kind of lubricant to use, see Recommended Fluids and Lubricants on page 6-12. If the level is below the bottom of the filler plug hole, you will need to add some lubricant. Add enough lubricant to raise the level to the bottom of the filler plug hole. Use care not to overtighten the plug. 5-47