Cadillac 2009 CTS - Manual (Page 360)

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.
Rear Axle
When to Check Lubricant
It is not necessary to regularly check rear 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.
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 rear axle, you’ll need to add some
lubricant. Add enough lubricant to raise the level to
the bottom of the filler plug hole.
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