it would be smart thing to do, so dust and dirt doesn't get into your fuel tank and build up. And so all your fuel doesn't evaporate.
Gas Cap is not on tight, or the seal leaks and you need to replace the cap.
how to replace the tether gas cap on a 1998 Buick Century?
find and remove gas cap, fill with gas and replace gas cap.
The gas cap light will go out automatically after you tighten, or replace the gas cap.
replace it
Most probable cause: Replace Gas Cap Most probable cause: Replace Gas Cap
gas cap seal bad , replace gas cap !!
check gas cap replace if necessary check EVAP lines for leaks and replace if necessary. Clear engine light and run vehicle a couple of days and see if it goes away.
If the gas cap tether is broken it can be replaced by removing the rubber plug or rivet that holds the tether in place. A new gas cap will need to be purchased and the rivet or rubber plug will have to be reinserted to hold it in the gas cap well.
Try changing the gas tank cap, if it does not help you might have to replace the charcoal canister because it does not release gas fume pressure.
The gas cap may not be tight enough or defective. Tighten it until you hear 3 clicks. If the light stays on replace the cap.
Replace the gas cap with a new one and tighten it 3 clicks.