Oldsmobile AURORA 2001 Owner's Manual page 264

When you put the 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.
The CHECK GAS CAP DIC message will come on if
the fuel cap is not properly reinstalled.
NOTICE:
If you need a new 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 your fuel tank and emissions system may be
damaged. See "Malfunction Indicator Lamp" in
the Index.
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