It’s no secret that modern cars are all about efficiency and meeting emissions standards. As such, they come packed with unique systems that control the amount of toxic waste that enters the atmosphere. One such system is the EVAP system.

Like any other part of the car, the EVAP system can fail from time to time. When that happens, it can trigger a number of check engine light codes, including the P0455 code.

In this article, we’ll be talking about the P0455 fault code, what it stands for, known causes, known symptoms, how to diagnose it, and eventually, how to fix it.

Here’s everything you need to know about the P0455 fault code.

What is the P0455 Code, and What Does It Mean?

The P0455 engine code stands for System Gross Leak Evaporative Emission, or Evaporative Emission Control System Large Leak Detected. Simply said, this code tells you that the ECU has detected a large leak in the evaporative emissions control system. It’s similar to the P0456 fault code, but these two are not the same. The p0456 is triggered when there is a small leak in the system.

The evaporative emissions control system, or EVAP as it’s commonly referred to, is used to prevent fuel vapors from escaping into the atmosphere. This system has become a mandatory addition to vehicles in 1976 and has been used ever since. Basically, the system prevents toxic vapors from escaping into the atmosphere by trapping them inside a dedicated vapor container. Once the engine meets certain parameters, these vapors are introduced during the intake cycle and are burned along with fresh fuel.

The installation of the EVAP system in cars has significantly reduced the amount of harmful vapors reaching the atmosphere and polluting the air, which is why the ECU illuminates the check engine light as soon as a leak is detected.

What Causes a Large EVAP Leak?

Whether the gas cap is defective, completely missing, loose, or damaged, it can trigger the P0455 engine fault code. It’s the most common cause for a large EVAP leak and is genuinely the easiest to fix. The reason why fuel caps fail is that we put a certain amount of stress on them every time we get gas.

The next cause for the P0455 code is a cracked or disconnected EVAP hose. When the car is running, there are certain vibrations that can cause the hose to disconnect and trigger the P0455 fault code. A cracked EVAP hose, on the other hand, happens less frequently because it’s not exposed to excessive heat, but it can become fragile due to age.

Another possible cause for the P0455 fault code is a cracked fuel tank. Most fuel tanks are made of plastic, and while fuel tanks aren’t easily damaged, they can crack if a rock hits them the wrong way, or if you hit other types of road debris. This will automatically lead to the P0455 code popping up on your dash.

The vapor canister can also cause this code to pop up if the canister is damaged or cracked. If you’re not sure what a vapor canister is – it’s a part of the EVAP system that absorbs fuel vapor. Its main function is to trap harmful vapors and prevent them from reaching the atmosphere, but also to send them back to the engine intake manifold through the purge valve.

What Are the Common Symptoms of P0455 Fault Code?

The most common symptoms of the P0455 code include decreased fuel economy, a smell of fuel in the passenger cabin, and a check engine light. As far as your car’s performance goes, you likely won’t notice anything different aside from a slight increase in fuel consumption. The car will drive the same as it did before and the idle will still be smooth.

The illuminated check engine light is the first symptom you’ll likely notice. To make sure you’re dealing with the P0455 fault code, you’ll need to use an OBD II scanner to read the stored codes in the ECU. This will give you all the information you need to know about what’s causing the check engine light.

As we’ve just mentioned, an increase in fuel consumption is one of the common symptoms of the P0455 fault code. Just beware that your fuel consumption could vary from season to season, which could mask the symptom of an EVAP leak.

Last, but not least, is the smell of fuel inside the cabin. When there’s a small leak, the smell of fuel isn’t that bad, but when there’s a large leak, the smell can get significantly stronger and is much easier to notice.

How to Diagnose the Cause of P0455 Code

To diagnose the P0455 code you’ll need an OBD II scanner, and an EVAP smoke machine leak checker.

The first thing you’ll want to do is use the OBD II scanner and make sure the P0455 code is the only one stored in your car’s ECU as there can also be other codes stored in the car that you didn’t know of.

Because one of the most common causes for the P0455 fault code is a faulty fuel cap, that’s where you should start. Visually inspect the gas cap for damage and wear. Check if the gas cap is fitted properly and forming a proper seal. The P0455 stands for a large leak, so minor damage and wear to the fuel cap usually won’t be causing this specific code to get stored in the ECU.

If everything looks good with the gas cap, you’ll need to visually inspect the EVAP hoses. Due to heat cycles, exposure and vibrations, these hoses can crack or come loose. Both of these issues are often obvious. Reseat the hose and use pliers or a screwdriver to tighten the clamps.

If you can’t visually find what’s causing the P0455 code, you’ll need to use an EVAP smoke machine leak checker. Only by using a smoke machine will you be able to see where the leak is coming from if you can’t see the issue.

How to Fix P0455 Code

A common fix for the P0455 engine code includes replacing the gas cap, replacing cracked or leaking EVAP hoses, or replacing/fixing a cracked fuel tank.

Replacing the gas cap is the easiest and most inexpensive fix for the P0455 code. Depending on the make and model, it can cost anywhere from $20 to $60, and replacing it is a pretty straightforward job.

If there’s a disconnected or cracked EVAP hose, it will need to be replaced or connected back again. If you noticed any of the EVAP lines disconnected, make sure to check all connections and replace the clamps holding the hoses in place.

On the other hand, if you found a cracked hose, it would be a good idea to replace them all, especially if it’s the first time you’re having this issue. Replacing EVAP hoses altogether is a good practice because you’ll reduce the possibility of experiencing the same issue due to the same cause.

After fixing the P0455 fault code, you’ll need to clear the ECU of the fault code for it to not appear again. This step isn’t required for all cars, but for those that don’t automatically delete the code from the ECU themselves.

Does P0455 Clear Itself?

In some cars, the P0455 code will clear itself after some time, while other vehicles need to have the code cleared with an OBD II scanner. The answer to this question mainly depends on the make and model of your car.

Even in cars that automatically clear the P0455 code, don’t expect the code to be cleared right away. The EVAP system checks for leaks while you drive your car for some time, so you’ll probably need to drive for a while before the check engine light turns off and the code is cleared.

Can You Drive with P0455 Code, and For How Long?

In theory, driving your car with a P0455 code won’t affect your car in any serious way. However, every issue that triggers the check engine light should be taken seriously and fixed as soon as possible.

Although the P0455 fault code won’t usually have an effect on the car’s performance, you’ll be violating regulations regarding emissions, and you’ll be polluting the environment. Aside from that, fuel vapor is actually flammable which exposes you to the risk of your car catching fire. This is pretty dangerous, and you wouldn’t want to find yourself fighting a fire in your car because of a minor issue that could have been only a few hundred dollars to fix.

Using Quality Parts Will Prevent The Same Issue From Happening Again

Keeping your car in good shape through regular maintenance is important if you want a reliable car. The best way to do this is by using Genuine or OEM parts.

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