Cadillac 2009 CTS Owner's Manual page 317

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 3-42.
The Tighten Gas Cap message in the Driver Information
Center (DIC) displays if the fuel cap is not properly
installed. See DIC Warnings and Messages on
page 3-57 for more information.
CAUTION:
{
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 3-42.
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