Cadillac GMC Yukon Denali 2005 Owner's Manual page 349

How to Check Lubricant
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 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.
What to Use
To determine what kind of lubricant to use, see
Recommended Fluids and Lubricants on page 6-12.
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