GMC 2003 Yukon Owner's Manual page 306

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.
4-24
3. Pull the push-pins and
lower air dam assembly
away from the
retainers until the lower
air 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 towards
the retainer until it locks
into place.
2. Push the flat end of the
push-pin towards the
retainer until it
locks into place,
making sure each is
secure.