How can I turn off the gas cap light

How to Reset the Warning Light Gas Cap That Is Loose or Missing

1. Turn off your vehicle's engine. Push button to unlock the gas cap door, if your vehicle is equipped with a locking gas cap door. ...
2. Step to the gas cap door. Open the door. ...
3. Replace the gas cap. ...
4. Close the gas cap door. ...
5. Use an OBD-II code scanner if the warning light does not disappear.

https://itstillruns.com/reset-gas-cap-loose-missing-7817331.html

https://www.theglobeandmail.com/globe-drive/culture/commuting/the-easiest-way-to-turn-off-your-cars-check-engine-light/article14223025
How to Reset the Warning Light Gas Cap That Is Loose or Missing

1. Turn off your vehicle's engine. Push button to unlock the gas cap door, if your vehicle is equipped with a locking gas cap door. ...
2. Step to the gas cap door. Open the door. ...
3. Replace the gas cap. ...
4. Close the gas cap door. ...
5. Use an OBD-II code scanner if the warning light does not disappear. ...
6. Continue driving the vehicle.

You said nothing about model, make, or year of vehicle, but on most vehicles, you have to turn the gas cap tightly until it clicks a couple of times when putting it on. If you only turn it (lightly) until it stops moving, it can work itself loose. If you are turning it until it clicks and it comes loose, you should replace the gas cap.

try disconnecting your positive cable on your battery for like 5 minuts

Yes...the cap needs to be on there or the purge system will register a leak. The light may not go out right away but usually will after about thirty miles of driving. (computer needs to go through a complete self test cycle).

Sometimes for this light to turn off you will need to reset the computer system that logged the code. Advance Auto and Auto Zone have a free service that will do this for you, they will also be able to tell you if the check engine light has logged a code for some other then the gas cap. Just go into Advance Auto or Auto Zone and say "Could you reset my check engine light for me?" they will grab their scanner tool and ask you to lead them to your vehicle, they will need to turn your car to the ON position but not start it.

p0440 is an evaporitive emission system system large leak detected generally on an 02 gm vehicle it is very common that the vent solenoid located by the fuel tank if you replace it the light will take a few days to clear its self. the vehicle runs tests on all sensors and systems and the test has to pass or fail a number of times before the pcm will turn on or turn off a check engine light.

try replacing the gas cap first and see if it helps any, on some vehicles, the fuel pump builds pressure inside the tank so it has the correct amount of pressure to send the gas to the engine. if the cap is missing, it can't build pressure.

yes the light is because of the gas cap being gone (sets code in evaporative emissions system), replace the gas cap, disconnect the battery for five minutes and that will turn of/reset the light, make sure u have the radio code before u do this, if u don't u will have no radio after the battery is disconnected..

Autozone or oreily just any gas cap just about will do. To force open use a flat head screw driver, hammer and pliers. Drive the FLAT tip screw driver into the gas cap and use the pliers to turn. These vehicles did not come factory with locking gas cap so some one has replaced it once before. Don't worry the worst you can do is ruin the gas cap which is no good to you any way.