2012 GMC Sierra Owner's Manual - Page 418

10-32 Vehicle Care What to Use Refer to Recommended Fluids and Lubricants on page 11‑12 to determine what kind of lubricant to use. How to Check Lubricant To get an accurate reading, the vehicle should be on a level surface. Rear Axle When to Check Lubricant It is not necessary to regularly check rear axle fluid unless a leak is suspected or an unusual noise is heard. A fluid loss could indicate a problem. Have it inspected and repaired. All axle assemblies are filled by volume of fluid during production. They are not filled to reach a certain level. When checking the fluid level on any axle, variations in the readings can be caused by factory fill differences between the minimum and the maximum fluid volume. All Except 1500 Series A. Fill Plug B. Drain Plug 1500 Series A. Fill Plug B. Drain Plug . . When the differential is cold, add enough lubricant to raise the level from 0 mm (0 in) to 3.2 mm (1/8 in) below the fill plug hole. When the differential is at operating temperature (warm), add enough lubricant to raise the level to the bottom of the fill plug hole.