Checking engine light is always on, I double checked the gas tank cap, but it still on

First, you have to have the trouble codes cleared from the computer memory to make the warning lights go off.
And the problem may be a leak in the gas tank venting system instead of the gas cap. The gas cap is the most often cause, but not always. You may have to get a shop to check for leaks.

Your problem is most likely coming from your gas cap. Your vehicle's gas cap may seem tight, but the rubber washer around the inner edge of the gas cap may be defective. Go purchase another gas cap for your car at one of the nearest auto part's location's nearest you. Change the gas cap and reset your vehicle's computer by taking the positive terminal off for a minute and replace the battery cable back on the vehicle. This method reset's your vehicle's computer. If the gas cap is the main problem, your check engine light won't come back on and your problem is solved. Gas is highly combustible and dangerous. always use precaution's when doing any work on your vehicle that require's working with any part's associated with any part's of the gas emission's system including the gas tank, gas cap, purge solenoid, charcoal canister, fuel filter, fuel pump, etc., etc. the gas smell can also be coming from a broken or faulty rubber gas line or the metal clamp's connected to the rubber hose's located between the gas tank fill valve and the gas tank itself. there are several black rubber gas hose's associated with the gas tank. have a qualified technician check the gas emission's system for any and all leak's gas also evaporate's fast, do to the combustibility again always use caution when attempting any and all repair's requiring checking the gas or emission's evaporation system. Sincerely Crystopper.

if the dealer charged you to fix it the should fix it for no extra charge

double check that the gas cap is the correct one and that it clicks 3 times at least when you put it on

If they forgot to tighten the hose clamps on the hose from the tank to the filler cap it could be setting it off. If they are all tight it was probably just the gas cap. The gas cap is usually ALWAYS the culprit. Let me know if this helps

Check that there are no other leaks in the gas filler neck or gas tank itself that would cause the gas cap error to cause the check engine light to go on.

A lack of pressure in the tank can cause the check engine light to go on, erroneously signalling that the gas cap is loose or missing.

Good luck on this repair.

Most likely an EVAP code. Need to scan it to get the specifics.

unplug the positive wire on battery and it will go off...make sure the gas cap is always tight and the engine isnt running while filling the fuel tank...beleive it or not this will cause the light to come on

By having it scanned and cleared with an OBD tool. This light comes on when it detects a problem. Could be a bad gas cap, or it could be a misfiring engine. The code you get from having it scanned will pinpoint the trouble area

the gas tank pump is malfuctioning or the check valve on the evpaerative canister purge valve is malfunctioning.