GMC Hummer H3 2008 Owner's Handbook Manual page 36

Malfunction Indicator Light
This light monitors the fuel, igni-
tion and emission control systems.
This light should come on when
the ignition is on but the engine is
not running, as a check to show
you it is working properly.
If it doesn't come on, then have it
fixed so it will be ready to warn
you if there is a problem.
If it stays on or comes on while you
are driving, there may be a prob-
lem with this system.
Problems with the system may be
detected before they are apparent.
Have it checked right away.
Section 1
NOTICE
If you keep driving your vehicle
with this light on, after a while,
your emission controls may not
work as well, your fuel economy
may not be as good and your
engine may not run as smooth-
ly. This could lead to costly
repairs that may not be covered
by your warranty.
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