GMC C-Series 2001 Owner's Manual page 91

Engine Air Control (If Equipped)
If your vehicle has this control, the handle is located on
the instrument panel just to the right of the steering
wheel. The control is activated by pulling the handle out
and turning slightly in either direction to lock it.
When the handle is pulled out, the engine air intake
supply is closed off from the front scoop and an under
hood air supply is opened. This control is intended only
for use in cold weather (32 _ F (0 _ C) or below) where
snow and ice might plug the external intake.
At temperatures above 32 _ F (0 _ C), keep the control
handle pushed in.
NOTICE:
Operating this vehicle with the engine air control
on when outside temperatures are above 32 _ F
(0 _ C), could lead to costly repairs not covered by
your warranty. It will also degrade fuel economy
and the engine will not run smoothly.
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