Buick 2005 LeSabre Owner's Manual page 249

When replacing the fuel cap, turn it to the right
(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 3-41.
If your vehicle has a Driver Information Center (DIC),
the GAS CAP LOOSE-CHECK CAP message will
be displayed if the fuel cap is not properly installed.
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 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 on
page 3-41.
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