If you’ve noticed the CEL turn on and you see that the flap on your gas tank is missing, you may think that it might be the reason that triggered it. So, can a missing fuel filler neck flap cause CEL to turn on?
The short answer is that it can, but it’s rare. Although there is little to no chance of it happening in a car with a gas cap, it can happen in cars with capless gas systems. Keep on reading to find out all about it. Let’s dive in!
What Is Fuel Filler Neck Flap
Before delving deep into this topic, you should clearly understand the parts involved here and what they do. That’ll make it much easier for you to grasp the discussion going on here. Let’s talk about the fuel filler neck first.
It’s a component whose main job is to transfer the fuel inserted into a vehicle into the fuel tank. The fuel filler neck is the point of entry in the vehicles when you load up on fuel. It shifts the fuel from the fuel nozzle to the fuel tank.
Now, let’s address the fuel filler neck fuel flap. Like the gas cap, its main job is to keep fuel from going out of the vehicle and polluting the environment. It was built in the 1970s.
The spring-loaded flapper was the first attempt to reduce carbon emissions during that time. Unleaded fuel was recommended in cars during that period to protect the environment.
Leaded fuel was more harmful, but it was cheaper. The majority of car owners were more interested in saving their money rather than protecting the environment. So, they used leaded fuel instead of unleaded fuel.
The flapper was the perfect solution designed by car manufacturers to counter this problem. It prevented leaded fuel from entering vehicles that were supposed to have unleaded fuel. Thus, carbon emissions were reduced, and it created a better environment.
Can A Missing Fuel Filler Neck Flap Cause CEL To Turn On [Explained]
Now, we’ve come a long way from the 70s and are far more advanced in reducing carbon emissions. Issues with fuel vapor control, including leaks, can pop up the check engine light.
A quick scan with an OBD-II scanner will reveal error codes like P0440, P0446, P0456, P0457, etc. All of them point to issues with fuel vapor control. And suddenly, you notice that the fuel filler neck flap on your car has gone missing. Could it trigger the CEL?
The short answer is that there’s little chance it’ll turn the check engine light on. Especially if you drive a car that has a gas cap. That’s because gas caps are also designed to prevent fuel leaks.
The missing fuel filler neck flap isn’t that important in these cars. It’d just go to the bottom of the fuel tank if it broke. Chances are that it’d do no damage and would stay there forever.
The gas cap would still keep the fuel vapor from going out. So, a missing fuel filler neck flap isn’t likely to trigger the CEL in cars with gas caps.
Now, let’s look at capless gas tanks. Ford was the first mover in building these types of cars that had no gas cap. It’s easier to load fuel in such cars. The flap is a more important component in such cars.
Its role is critical in preventing the fuel vapor from going out, as there are no gas caps here. But even in these types of cars, it’s not common for a missing flapper to turn on the check engine light.
There’s a high possibility that something else is wrong with your car. And to know what’s up with that, keep on reading. But if it is the missing flap that’s causing the issue, you can get a universal flap and solve this problem.
What Fuel Issues Can Actually Cause The CEL
By now, you should understand that the chances of the missing fuel filler neck flap triggering the CEL are little to none. But if you see the error codes I mentioned, there’s a high likelihood that it’s one of these issues that’s causing the check engine light to come on:
1. Loose Gas Cap
The number one reason that can cause the check engine light to turn on and trigger the error codes we mentioned is a loose gas cap. It’s much more likely to trigger the CEL than the missing gas tank flap.
Sometimes, the message “check fuel cap” will pop up on your dash, indicating you to check the gas cap. If you think about it – the gas cap is the device that keeps the fuel from leaking.
So, if the gas cap is not sealed properly, it’s obvious it can cause the fuel vapor to leak. The cap needs to be closed fully to prevent any leaks. The only instance in which a missing flap has a strong likelihood of turning on the CEL is if the gas cap doesn’t sit properly because of it.
Yes, in some cars, the gas cap needs a flap to seal the fuel system. But even those cars are rare, and you’ll need the opinion of a professional mechanic to know if that’s the case with your car.
If a loose gas cap has caused the CEL to come on, you’re lucky, as it’s an easy fix. All you have to do is tighten it, and your problem will be solved. However, there’s also the chance that it can be caused due to the gas cap not sitting properly because of the missing flap.
In that case, you’ll have to replace the flap with a universal one and ensure the gas cap sits properly. That’ll seal the fuel leak, and you can keep driving your vehicle without a hitch.
At times, the gas cap may also be dirty. If you find significant debris or dirt, clean it and add some silicon grease before putting it on and tightening it. Steer clear of using any mineral grease on it. If that doesn’t work and the gas cap is broken, replace it with a new one.
2. Leaky Fuel Filler Neck
A leaking fuel filler neck can also cause the check engine light. When the fuel filler neck isn’t entirely sealed, fuel vapor will enter the environment. The EVAP system of your car will get messed up because of it.
The car’s engine won’t be able to reuse the vapors from the fuel tank when there’s such a leak. The fuel filler neck is usually made of metal or rubber and can get worn out with time.
Luckily, a leaking fuel filler neck is easy to identify and diagnose. Apart from the CEL being turned on, the other symptoms of bad fuel filler neck are:
Smell Of Fuel
It’s normal if you get a slight smell of fuel when you’re filling up the fuel tank. But if the smell stays on for a long period or gets stronger, it’s a good indicator of a leak in the fuel filler neck.
Visible Fuel Leaks
A tell-tale sign of a bad filler neck is seeing fuel leaks as you’re loading fuel into your vehicle. Even if you notice the leak later on from the side of the vehicle, it still points at a leaking fuel filler neck.
If you’ve noticed the symptoms mentioned above, there’s a high chance that you have a leaky fuel filler neck. You’ll have to deal with this issue soon, as leaving it unattended can lead to a potential fire hazard.
So. how do you fix a leaky fuel filler neck? You can take it out of your car and locate the holes where the holes have developed. Then, you can seal it with epoxy, glue, or fiberglass. Put it back on, and you’re done.
Here’s how I sealed the holes in the fuel filler neck of my GMC truck:
Step 01 – Get The Fuel Filler Neck Out
Remove the gas cap and unscrew two of the three bolts that hold the fuel filler neck in place. Then pull the ground wire out with a 10mm wrench.
Two rubber hoses are connected to the fuel filler neck. Loosen the hose clamp closer to you and get the rubber hose out.
Now unscrew the last bolt and disconnect the remaining rubber hose. Pull off the fuel filler neck.
Step 02 – Seal The Holes
First, clean the filler neck and identify where the rust holes are. Place an aluminum foil top over the holes to cover them so they can pack against the JB weld or epoxy glue you’ll use.
Marine JB Weld was used in this case. Mix parts a and b equally until you get a consistent color. Apply the mixture evenly and leave it for at least a day so that it can cure properly.
Step 03 – Finishing Touches
When the JB weld hardens, there’ll be a little extra part. Hatch it back and forth until it’s nice and rounded. Apply a little paint to prevent the filler neck from getting rusted again.
Reverse the steps you did when you took it out and put it back in its place, and you’re done.
That’s all it took to replace it. The process of taking the fuel filler out may vary a little bit depending on your car. Attempt to fix it only if you have knowledge and experience working with these vehicles.
Sometimes, there could be too many holes in the fuel filler neck, which may be beyond repair. Or, you may need more expertise to carry out this task of sealing the filler neck. In that case, you should hire a professional mechanic and get it replaced.
3. Dirty Fuel Filler Flap
When talking about cars with a capless gas system, it’s not only a missing gas tank flap that can trigger the CEL. A dirty fuel filler neck flame will also have the same effect.
That’s because dirt and debris can build up more easily on these cars. The most common error code thrown because of this issue is the P0457 error code which indicates an evaporative emission control system leak.
Thankfully, getting rid of this problem is easy as all you’ll have to do is clean the filler area filled with dirt. One method to remove the dirt from the filler area is to take it in and out of the dirty filler until the debris breaks loose. Remember that this process may take some time.
Don’t rush through it, and be gentle while doing it. An easier way to get it done would be using an additional substance like compressed air or WD-40. If you use compressed air, blow the filler first, place the funnel, and pull it out. Keep repeating it until the dirt is out.
It’ll also take a little while but not as long as it would with the funnel itself. You can also try the same thing with a brake cleaner or WD-40 if you don’t want to use compressed air. Either way, the idea is to get the dirt out and remove the check engine light.
Should You Use Cars With Capless Gas Systems
Since Ford introduced the capless gas system to make filling up fuel in your car easier, several other companies have entered the scene. General Motors, Honda, and Fiat are some examples of automakers that have also integrated capless fuel fillers in their vehicles.
The main advantage of using such cars is that you’ll no longer have to open up the gas time you fill the car with fuel. You can directly attach the pump to the gas nozzle and start filling the gas. It’s way more convenient than taking on and off the gas cap every time you want to fill fuel.
The spring-loaded flap you see is more important in these cars as it keeps the fuel vapor from escaping. If it gets dirty, it can trigger the CEL light. You already know how to solve that.
The obvious benefits of using such cars are that it’ll save you time and is much more convenient. Besides that, you won’t have to worry about that gas smell on your hands. You can also rest assured that your car won’t get scratched due to the gas cap.
But there are some noticeable downsides as well that are commonly being reported as they continue getting more popular. Here are the most noticeable disadvantages of such vehicles:
- It can easily trigger the CEL when the flap gets dirty or goes missing.
- The fuel won’t open at times, and you won’t be able to put the fuel nozzle in.
- You’ll have to stop filling your car when you hear the gas station pump clicking if you don’t want the car to smell like gas.
- The gas pump can easily get stuck sometimes.
Though these are annoying downsides to such vehicles, you can solve them in most cases with a little bit of patience. Whether the pros outweigh the cons is something you’ll have to decide on your own.
How To Fill Fuel In Cars With Capless Gas Tanks
Generally, filling fuel in capless gas tanks is easy, and the owner’s manual has clear instructions on how to do it. In most cases, you’ll open the gas door, insert the fuel nozzle, and wait for the tank to become fuel.
When that happens, you’ll release the pump trigger, wait for a few seconds, and take out the pump nozzle from the fuel filler. That’s easy. But sometimes, you may run out of gas and may be intrigued to use a portable fuel container.
I’m here to warn you that you should only do it with a special funnel that’s provided with your vehicle. If you don’t already know where it is, check your owner’s manual and find out where it is. It’s normally located in the rear storage area or the trunk.
Here’s how you can use it correctly:
Open the gas door and insert the special funnel. And make sure you push it in all the way. Otherwise, it can come out. Then add fuel from the container via the funnel.
And here’s the most important piece of advice – if you can’t find the special funnel, don’t use another funnel or the fuel container nozzle to fill the fuel in your car.
It can damage the spring-loaded flap in your car. That’ll trigger the warning light on your dash, and you’d have to take it to a mechanic for repair.
Is leaving the gas cap off dangerous for your car?
Normally, there are no other catastrophic dangers that’ll arise due to not putting on the gas cap. But, it’ll trigger the EVAP code, leak more fuel into the environment, and also reduce fuel efficiency.
How long does the check engine light stay on after tightening the gas cap?
After you tighten the gas cap, the check engine light should go away after 100 miles of driving or so, as the system will reset itself by then. But if it doesn’t go away, there are most likely other issues as well that are causing it to stay on.
How much does a gas cap cost?
If your current gas cap is broken, it’s always recommended to replace it with an OEM gas cap. Depending on your vehicle, it’ll generally range between $20-$100.
How long does it take to replace a fuel filler neck?
Normally, a competent mechanic shouldn’t take more than an hour or two to replace a fuel filler neck.
How to find the special funnel in capless gas tank cars easily?
If the location of the special funnel isn’t obvious in your vehicle, do a quick search for the manual online. Press “Ctrl+F” and type “funnel” or “refueling” to find it. Or you can call the customer support number and find it out.
Can the fuel filler neck flap miss cause the check engine light to turn on? By now, you know all about it after completing this article. It’s rare and much more common for issues like a loose gas cap or a leaking fuel filler neck to be the culprit here.
Hopefully, you’ll easily figure out what triggered the CEL in your case after a thorough diagnosis and solve it. Comment below if you have any more questions about the gas tank flaps.
Note: You can also read our guide on can aftermarket exhaust cause check engine light.
About John M
John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.