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The description for a fuel tank cap says:

You can prevent unnecessary service costs by replacing the gas cap on modern vehicles before they go bad and the check engine light appears.

Is this advertising baloney? Is there actually something that goes bad in a car if one waits until the check engine light goes off before replacing the fuel tank cap? It only takes driving on one or two full tanks until the system recalibrates. The check engine light will disappear and all will be well again. No?

  • I'm interested to see what answers come up here. I just don't see how a bad fuel filler cap would adversely impact fuel delivery and fuel management, especially when fuel trims exist. – Zaid Jan 8 '16 at 3:21
  • Your question is answered here. The CEL is more for emissions regulations than vehicle operation – Zaid Jan 8 '16 at 3:25
  • I would say this means that IF the CEL goes off due to bad pressure in the tank then you would have to take it to a shop, read the code, etc., which would consume time and money. I can't imagine what permanent damage could a faulty tank cap do. Misleading phrasing to encourage purchasing. – I have no idea what I'm doing Jan 8 '16 at 7:56
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I was able to find the exact verbiage on Amazon for a Toyota gas cap. It implies that you will get a CEL (check engine light) and you could, which could cost you money to get it checked out.

Here is the listing: Genuine Toyota (77300-33070) Fuel Tank Cap Assembly by Toyota Genuine OEM Toyota Gas Cap New in Original Packaging with Seal. The typical life span on gas caps is 5 - 6 years.

You can prevent unnecessary service costs by replacing the gas cap on modern vehicles before they go bad and the check engine light appears

However, I had a CEL come on, due to a tiny vacuum leak at the gas cap and I drove it for quite a while, over a year, with no ill effects. I didn't know that the solution was a new gas cap and didn't want to pay the expense of having someone locate the leak. I found out later the gas cap was the usual issue and the light went off when I replaced the gas cap. If the light comes on over something like this it isn't going to hurt anything.

Where I live in St. Louis, AutoZone, Oreillys, and Advanced Auto give you a free reading for a CEL, but I know shops were still charging for readings if you asked for one.

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    It's probably worth mentioning that the reason the gas cap exists is both to prevent evaporation of the fuel into the atmosphere (prevent pollution) and to prevent other stuff (such as water) getting into the fuel. If the cap is allowing sufficient amounts of water into the fuel, it could indeed cause problems. Generally, though, I agree that replacing a cap before it has any problems is only a good idea to those who sell gas caps. – Edward Jan 8 '16 at 16:12
  • Good point, but on my car (Mitsubisihi), the leak can be very very slight before the CEL comes on, which is a good thing. Normally, the rule of thumb I go by is when you see a CEL get it checked out and fixed as soon as possible before the problem(s) get more expensive. Ignoring a CEL normally means more work down the road. – James Drinkard Jan 18 '16 at 17:04
  • Where you been? Not coming around here anymore? Liked your responses.....hope all is well. – Ppoggio Mar 20 '16 at 4:57
  • I've been fixing my cars and working overtime at work. Nothing to do with the site. – James Drinkard Mar 20 '16 at 20:02
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I've never seen replacing the fuel cap as any part of the maufacture recommend maintenance. Some vehicles now don't even have one, the seal is made internally or by the fuel hatch door.

Once on an older vehicle, I had the service engine light come on because of the fuel cap seal. I couldn't find a replacement cap or O ring to fit, so I just took the seal off and flipped it around. Fixed the issue.

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