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Discussion Starter #1
I stopped this afternoon and filled the tank of my Sonata and I later noticed that my check engine light is on. I did notice that the filler cap does not click when I screw it back onto the filler neck. I do know that there is a label stating that I should tighten the cap until one click is heard and I have heard stories about loose fuel tank caps causing the check engine light to appear due to insufficient fuel tank pressure. Could I have a defective cap that is causing the problem? I will take it to my local shop tomorrow to confirm this or find out the problem for sure.
 

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Discussion Starter #5
Well it might be just what you said. The filler cap not sealing. I think a new cap is cheap so why not give it a go before taking it to a shop.
Well considering that the one that is on the car does not click as it should, I ordered one from Amazon. It is an OEM Hyundai gas cap. It does say on the cap to tighten until one click is heard or the CE light will come on right on the cap. It wasn't but $20 and it will be here Thursday. I will post an update when it is installed and the light is off. Thanks!
 

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Since it happened with the refueling and your cap does not seem to work correctly that is a good place to start. Dont expect the CEL to turn off immediatly when you install the new cap, sometimes it takes a little while and a few starts to get the CEL to go off.

Another common cause associated with CEL after refueling is caused by overfilling and the evap canister is filling or full of fuel because the owner tops off the tank frequently. If it is the canister sometimes it will fix itself by evaporation but more often you have to replace the canister.
 

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Discussion Starter #7
@xaran, Thanks for the information. I hope I didn't overfill the tank but I was pushing to round off the total amount to the nearest dollar. I will keep that in mind from now on. I only fill up the tank when it reaches a quarter tank of fuel or the gas price has dropped after the holiday price gouging... er, uh, I mean price increase. :rolleyes: :D
 

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Discussion Starter #9
Don't do that.
Point taken. It is just a habit I had from driving a 1997 $Runner for 19 years. After the nozzle would automatically shut off while fueling, the tank would hold 3 more gallons. It took a few more clicks to finish adding those 3 gallons but that added about 60 miles of driving distance. I will make a note to remind myself that the Sonata doesn't like being filled to the top and stop pumping gas after it shuts off the first time. See, you can teach an old dog an new trick. :D
 

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You should only fill until the pump cuts and no more. Adding can contaminate the evap canister and cause other related problems.
 

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Actually no car likes to be fueled full.

It is explained better in this website

How does a gas pump know when my tank is full?

This mechanism has been around for a long time, so it is safe to say there is not a miniature camera inside the nozzle hooked to a microprocessor. It's purely mechanical -- and ingenious.

Near the tip of the nozzle is a small hole, and a small pipe leads back from the hole into the handle. Suction is applied to this pipe using a venturi. When the tank is not full, air is being drawn through the hole by the vacuum, and the air flows easily. When gasoline in the tank rises high enough to block the hole, a mechanical linkage in the handle senses the change in suction and flips the nozzle off.

It might cause problems to your car and your wallet.

I used to have that custom decades ago, and one day my brand new Chrysler Reliant didn't want to start. The dealer mechanic came and asked me what was the last thing I did with my car, and I told him I filled up with gasoline up to the top. He almost laughed. He used a small pump and removed some gasoline and the car started without problems. Since then I learned my lesson.

Here is a site where you can read a little more about it.


“By topping your fuel tank off, it can either overwhelm your evaporative system and break something or cause a hazardous leak by the excess pressure in the system,” says Ed Nemphos, owner of Brentwood Automotive in Baltimore, who adds gas needs extra room to expand in the tank.


Highly rated mechanics on Angie’s List that we spoke to agree with the Environmental Protection Agency, which has outlined three main areas where gas topping can have negative effects.

And there is more information given.
 

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Discussion Starter #12
I thank you all for the information and education. With what I have learned on this subject, I am surprised that my 1997 4Runner never had any of these problems. I used to regularly fill the tank up to the top of the neck of the filler tube. Either I was very lucky or that year model did not have an evaporative canister. My research on these devices states (if I read this right) that the use of these came in around 1998. Thanks again for the education and fair warnings. (y)
 

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With the older cars there was no way of knowing what damage was done and if there was room in the tank for expansion you never found out. It wasn't till OBD2 started and you guys with emission testing it all came out in the open.
 

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Discussion Starter #14
**UPDATE

I ordered a replacement OEM gas cap from Amazon and received it's generic version... twice. The generic version was the same except for the writing and warnings on the cap but in the end, Amazon refunded my money and told me to keep the second cap anyway so I installed it. The new one does click as it should so I am OK with it.

The good news is that the CEL is gone already. :D (y)

Thanks to all of you who gave me advice and most of all, an education about fueling my Sonata. (y)(y)
 
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