GMC 2002 Envoy - Manual (Page 336)

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How to Check Lubricant
To get an accurate reading, the vehicle should be on a
level surface.
The proper level is from 0 to 3/8 inch (0 to 10 mm)
below the bottom of the filler plug hole.
What to Use
Refer to the Maintenance Schedule to determine what
kind of lubricant to use. See “Recommended Fluids and
Lubricants” in the Index.
Four - Wheel Drive
Lubricant checks in this section also apply to these
vehicles. However, there are two additional systems that
need lubrication.
Transfer Case
When to Check Lubricant
Refer to the Maintenance Schedule to determine how
often to check the lubricant. See “Periodic Maintenance
Inspections” in the Index.