GMC 2006 Sierra - Manual (Page 473)

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,
located on the front axle, you may need to add some
lubricant:
• When the differential is cold, add enough lubricant to
raise the level to 0 to 3/8 inch (9.5 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 (Gasoline Engine)
on page 6-14.
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