Cadillac 2004 DeVille Owner's Manual page 300

To inspect or replace the filter, do the following:
1. Loosen and remove both wing screws on the top of
the engine air cleaner/filter cover.
2. Lift up the outboard side of the cover at an angle
while pulling toward you. This is necessary due to
the three tabs located on the rear of the cover.
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3. Remove the engine air cleaner/filter element and
any loose debris that may be found in the air
cleaner base.
4. Replace the air filter element.
Follow these steps to reinstall the cover to the engine
air cleaner/filter housing:
1. Align the three tabs located on the back of the cover
with the three slots on the back of the housing.
2. Push the cover slightly down and towards the
engine to engage the tabs in the slots and align
the two wing screws.
3. Engage and tighten the two wing screws on the
top of the engine air cleaner/filter housing cover.