GMC 2006 Sierra 1500 Pickup Owner's Manual page 330

When you are back on roads, though, be sure to
replace the air dam.
Notice: Operating your vehicle for extended
periods without the front bumper lower air dam
installed can cause improper air flow to the engine
and may allow things like fog lamps or tow hooks
on the front of your vehicle to be damaged. Always
be sure to replace the front bumper air dam when
you are finished off-road driving.
4-18
3. Pull the push-pins and
lower dam assembly
away from the retainers
until the lower dam
is free.
To reinstall the lower air dam, do the following:
1. Line up each push-pin
with its intended
retainer and push the
washer portion of the
push-pin toward the
retainer until it locks
into place.
2. Push the flat end of
the push-pin toward the
retainer until it locks into
place, making sure
each is secure.