Chevrolet HHR 2010 Owner's Manual page 306

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 4-35.
The CHECK GAS CAP message displays on the Driver
Information Center (DIC) if the fuel cap is not properly
installed. See DIC Warnings and Messages on
page 4-48 for more information.
6-12
To close the fuel door securely, push the door to the
closed position.
WARNING:
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If a fire starts while you are refueling, do not
remove the nozzle. Shut off the flow of fuel by
shutting off the pump or by notifying the station
attendant. Leave the area immediately.
Notice: If you need a new fuel cap, be sure to get
the right type. Your dealer/retailer can get one
for you. If you get the wrong type, it may not fit
properly. This may cause the malfunction indicator
lamp to light and may damage the fuel tank and
emissions system. See Malfunction Indicator Lamp
on page 4-35.