GMC 2004 Sierra 1500 Pickup, Owner'S Manual, Page: 461 / 588

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’ll 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.
When to Change Lubricant
Refer to the Maintenance Schedule to determine how
often to change the lubricant. See
Scheduled
Maintenance on page 6-4.
What to Use
Refer to the Maintenance Schedule to determine what
kind of lubricant to use. See
Recommended Fluids
and Lubricants on page 6-14.
Front Axle
When to Check 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.
Automatic Transfer Case
5-61