A faulty gas cap is a major annoyance that can plague your car if you don’t take care of it. It’s hard to tell exactly what causes a gas cap to fail but there are a few guesses we can take. Grit and grime getting in between the threads of the cap and filler wearing away at it is usually a contributing factor. Sometimes it’s just general wear. Plastic isn’t that durable, and occasionally just gives out.

If you suspect your gas cap is failing there are a few signs to look for. You may experience one, some, or all of these symptoms.

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Symptoms Of A Faulty Gas Cap

Your gas cap’s function is to create a seal around the filler neck so that fumes from the fuel can’t escape your tank. When it doesn’t do this there are signs that point you to it, some are more obvious than others but are easy enough to notice nonetheless.

Smell of Gasoline

This might not be as noticeable but, without a cap to seal the filler, fuel vapors are allowed to escape into the atmosphere. In an enclosed space like a garage, the smell of gasoline might be more prevalent because it can collect.

Dashboard Light/ Check Engine Light

Most cars will illuminate some sort of dashboard light when the gas cap isn’t properly seated. Many cars, like my 2008 Ford Escape Hybrid, even have a light that is specifically for the gas cap. Goes to show that not tightening a gas cap all the way is a common enough problem that manufacturers noticed and created a warning light for it.

If your car doesn’t have a specific light for the gas cap, it may just throw up a generic check engine light. In the event your gas cap is completely off and driven, the vehicle will most likely display a check engine light because it will read as non-ready.

All cars with obd2 will go through a systems check when you start it to make sure all the different components are in order. The gas cap is part of the fuel and emissions system so if it’s not on there when you drive, the car’s computer will throw a check engine light for non-readiness.

Vehicle Refusing To Start

Cars are jam-packed with computers and sensors these days, and some, in particular, have sensors that restrict vehicles from starting if they don’t detect a tight seal from the gas cap. This is usually done as a safety measure to prevent vehicles from driving off in the event you forget to remove the filler nozzle at the pump.

I know what you’re thinking, who could be that dumb? Have a look at this hilarious compilation by
Jacob Zimpfer from Youtube and you’ll see plenty of examples.

Is A Faulty Gas Cap Bad For My Car?

Mostly, a faulty gas cap is an annoyance that can be solved rather easily, similar to our guide on getting rid of streaky windshield wipers.

Although a faulty gas cap can’t actually cause damage to your vehicle, there can be some “potentially” dangerous scenarios in extreme cases.

Leaking Fumes Are Dangerous

As we know, one of the symptoms of a faulty gas cap is leaking fumes. Those fumes can be harmful to humans if we breathe them on a continuous basis.

Gasoline vapors are flammable, and if concentrated in small spaces like a garage can cause a fire to spread. If you keep power tools on charge, or any other thing that may potentially cause a spark, it could ignite the fuel vapors. This scenario is very unlikely but possible under the right circumstances.

How To Fix A Faulty Gas Cap

Replacing the gas cap entirely is the only real permanent fix. This makes sure that you have no sealing issues and that you won’t have problems again in the future.

You may read in other places about using sealants or other products around your current gas cap to make it work, but I would advise against that. It probably won’t last as a fix, and why bother?

It’s so affordable to just get another gas cap.

Where To Get A Replacement a Gas Cap

Generally, a gas cap should cost under $30 new for most cars. If you have a very expensive vehicle it could range as high as couple hundred bucks, so shopping around might be worth the hassle.

Buy Used

Buying a used gas cap would be my first choice. Depending on where you source from, you’ll be able to select an OEM part for, hopefully, less than the cost of a new one.

Just a good rule to follow on all part purchases: double-check the price you’re paying for your used parts against what the part costs new. I’ve had many instances where the used parts were the same price, if not more expensive, than new!

eBay motors

Online places like eBay are a great resource to find deals on new and used parts, especially small items like gas caps because they’re easily packed and shipped.


Junkyards are an underutilized resource these days. They’re a goldmine if you’re looking for OEM parts that you can go get today. You can find a local place to you by searching online and most will have an inventory of the parts they carry. This is a solid choice to buy a replacement gas cap.

Buy New

If you have to buy a new gas cap, you’ll find many third-party manufacturers offer them for a lot less than OEM. These can work well and save you a bunch of money, however, just know often these manufacturers don’t have the same quality control standards as OEMs so there could be fitment issues.

If your car doesn’t have third-party parts available, then the original is the only option you have. Shop around online; you should be able to find a good deal. If you’re thinking about buying directly from the dealership, just know this is usually the most expensive way to buy parts. Dealerships have rather large markups.

In Sum

A faulty gas cap can be a major annoyance but, luckily, is an easy fix. Get it done the right way and it should last you for the life of the vehicle.

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