Cadillac 2004 CTS Owner's Manual page 294

To remove the fuel cap, turn it slowly to the left
(counterclockwise). The fuel cap has a spring in it;
if you let go of the cap too soon, it will spring back to
the right.
5-8
While refueling, hang the
fuel cap by the tether from
the hook on the fuel door.
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CAUTION:
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.
Be careful not to spill fuel. Don't top off or overfill your
tank, and wait a few seconds after you've finished
pumping before you remove the nozzle. Clean fuel from
painted surfaces as soon as possible. See Cleaning
the Outside of Your Vehicle on page 5-89 .
When you put the fuel 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 on
page 3-42 .