Cadillac CTS 2008 Owner's Manual page 328

How to Inspect the Engine Air
Cleaner/Filter
To inspect the air cleaner/filter, remove the filter from
the vehicle and lightly shake the filter to release loose
dust and dirt. If the filter remains caked with dirt, a new
filter is required.
To inspect or replace the engine air cleaner/filter, do the
following:
1. Turn the ignition off.
2. Remove side cover by pulling up on front of cover.
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3. Disconnect electrical connector from air box.
4. Loosen the screw on the clamp holding the air outlet
duct in place. Do not pry the clamp off. Position the
duct aside.
5. Remove the rubber hose from the air cleaner
housing mounting arm. Position the rubber hose
aside.