Hummer 2003 H2 Owner's Manual page 341

CAUTION:
If you get fuel on yourself and then something
ignites it, you could be badly burned. Fuel can
spray out on you if you open the fuel cap too
quickly. This spray can happen if your tank is
nearly full, and is more likely in hot weather.
Open the fuel cap slowly and wait for any "hiss"
noise to stop. Then unscrew the cap all the way.
Be careful not to spill fuel. Clean fuel from painted
surfaces as soon as possible. See "Cleaning the Outside
of Your Vehicle" in the Index.
When you put the fuel cap back on, turn it to the right
(clockwise) until you hear a clicking sound. Make sure
you fully install the cap. The diagnostic system can
determine if the fuel cap has been left off or improperly
installed. This would allow fuel to evaporate into the
atmosphere. See "Malfunction Indicator Lamp" in
the Index.
NOTICE:
If you need a new fuel cap, be sure to get the
right type. Your dealer can get one for you.
If you get the wrong type, it may not fit properly.
This may cause your malfunction indicator lamp
to light and may damage your fuel tank and
emissions system. See "Malfunction Indicator
Lamp" in the Index.
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