GMC 2009 Sierra - Manual (Page 359)

How to Check Lubricant
To get an accurate reading, the vehicle should be on
a level surface.
For AWD 6.2L applications, the proper level is from
0.04 inch to 0.75 inch (1.0 mm to 19.0 mm) below
the bottom of the filler plug hole, located on the rear
axle. Add only enough fluid to reach the proper level.
For 2WD 6.2L applications, the proper level is from
0.6 inch to 1.6 inches (15 mm to 40 mm) below
the bottom of the filler plug hole, located on the rear
axle. Add only enough fluid to reach the proper level.
What to Use
Refer to the Maintenance Schedule to determine what
kind of lubricant to use. See Recommended Fluids
and Lubricants on page 6-12.
Front Axle
When to Check and Change Lubricant
It is not necessary to regularly check front axle 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.
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