Pontiac Montana SV6 2007 Owner's Manual page 416

While refueling, let the fuel cap hang by the tether.
CAUTION:
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If you spill fuel 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.
416
Be careful not to spill fuel. Do not top off or overfill
the tank and wait a few seconds after you have
finished pumping before removing the nozzle.
Clean fuel from painted surfaces as soon as
possible. See Washing Your Vehicle on page 501.
When replacing the fuel cap, turn it clockwise until it
clicks. Make sure the cap is fully installed. 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 on page 222.
The CHECK GAS CAP message will be displayed
in the Driver Information Center (DIC) if the fuel
cap is not properly installed. See DIC Warnings
and Messages on page 237 for more information.