GMC 2009 Sierra - Manual (Page 331)

3. Remove the engine air cleaner/filter from the
housing. Care should be taken to dislodge as
little dirt as possible.
4. Clean the engine air cleaner/filter sealing surfaces
and the housing.
5. Inspect or replace the engine air cleaner/filter.
6. Reinstall the cover and tighten the screws.
7. Reset the air filter restriction indicator, if the vehicle
has one, by pressing the top button on the indicator.
{ CAUTION:
Operating the engine with the air cleaner/filter
off can cause you or others to be burned.
The air cleaner not only cleans the air; it helps
to stop flames if the engine backfires. If it
is not there and the engine backfires, you
could be burned. Do not drive with it off,
and be careful working on the engine with
the air cleaner/filter off.
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