Pontiac 2003 Montana Owner's Manual page 371

Carrier Assembly-Differential
(Rear Drive Module)
When to Check and Change Lubricant
Refer to the Maintenance Schedule to determine how
often to check the lubricant and when to change it. See
Part A: Scheduled Maintenance Services on page 6-4.
How to Check Lubricant
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.
A fluid loss could indicate a problem; check and have it
repaired, if needed.
What to Use
Refer to the Maintenance Schedule to determine what
kind of lubricant to use. See Part D: Recommended
Fluids and lubricants on page 6- 16.
To get an accurate reading, the vehicle should be on a
level surface.
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