P0455 Code: Evaporative Emission Control System Large Leak Detected

Because you notice that your check engine light is on all of a sudden, you plug in your scan tool into the OBD-II port to check what the issue is. Turns out, the P0455 code has been stored. While you may be looking at a potential gas cap issue, you’re not dismissing the fact that there may be another problem causing this trouble code to set. What does this code mean and what problems could be causing it? Could you still drive with a code P0455 present? Answer all these questions and more with this quick guide.

What Does the P0455 Code Mean?

Diagnostic trouble code (DTC) P0455 stands for “Evaporative Emission Control System (EVAP) Large Leak Detected”. Your car’s computer will set the code when it determines there’s a significant leak in the EVAP system.

Users have reported code P0455 for the following makes: Chevrolet (especially on a Chevy Silverado), Dodge, Ford, Jeep, and Nissan.

P0455 on Some Chevrolet Vehicles

Code P0455 may appear on some Chevy vehicles. On a 2010 Chevrolet Silverado 1500 LS 5.3L V8, for example, this DTC is set when “the EVAP system is not able to achieve or maintain a calibrated level of vacuum within a set amount of time.”

The code appears in a 2010 Chevrolet Silverado 1500 5.3L V8 because of the following conditions:

• The ignition voltage is between 11–32 volts.
• The barometric pressure (BARO) is more than 70 kPa.
• The fuel level is between 10–90 percent.
• The engine coolant temperature (ECT) is less than 35°C (95°F).
• The intake air temperature (IAT) is between 4–30°C (39–86°F).
• DTC P0455 runs once per cold start when the above conditions are met.

For the circuit/system testing of Chevy vehicles, it’s important to note that larger volume fuel tanks and/or those with lower fuel levels may require several minutes for the floating indicator to stabilize.

Note: The definition of trouble code P0455 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What Is an EVAP System and How Does It Work?

Okay, that’s great. But you’re probably wondering: what’s an EVAP system? Basically, it’s a collection of components that work together to prevent fuel vapors from escaping into the atmosphere.

Basic (non-enhanced) EVAP systems were first introduced in the 1970s. In 1996, automakers began fitting new vehicles with enhanced systems that can detect a leak, then set a code, such as P0455.

The system creates a sealed environment designed to capture, store, and purge volatile fuel vapors from the fuel system.

Although system designs vary, typically, the primary components found within an EVAP system include the fuel tank, gas cap, purge valve, vent valve, and EVAP (charcoal) canister.

When the engine is off, fuel vapors are stored in the charcoal canister, rather than being allowed to escape into the atmosphere.

Once the engine is running and the appropriate conditions are met, the purge valve opens to allow the vapors to enter the engine, where they are burned during the normal combustion process. The vent valve, which allows fresh air to enter the charcoal canister, is usually open unless the system is running one of its self-tests.

Your engine control module (ECM) controls both the purge and vent valves via electronic solenoids. The ECM also monitors EVAP system operation, checking for leaks and other issues.

EVAP System Tests and the P0455 Code

To ensure that the EVAP system is working properly, the ECM performs fuel vapor leak tests. These tests may occur when your vehicle is parked (the engine is switched off) or while it’s running.

During these vapor leak tests, the ECM sends a signal to close the vent and purge control valves. After that, the ECM monitors the entire system for pressure changes or vacuum loss. The ECM then stores codes depending on the potential size of the leak. Large leaks are recorded as code P0455, while small leaks are recorded as P0456.

What are the Possible Causes of the P0455 Code?

Wondering what’s causing the issue? Here are some of the possible reasons why you’re getting this OBD-II code:

• Gas cap is missing, left open, or not secured properly
• Gas cap is faulty or damaged
• Fuel tank filler neck is deformed
• Fuel tank is cracked or damaged
• Fuel tank pressure sensor is faulty
• Charcoal EVAP canister is cracked or damaged
• EVAP hoses and clamps are disconnected, cracked, or punctured
• EVAP vent solenoid is faulty or stuck open
• EVAP purge valve is faulty and stuck open

What are the Common Symptoms of the P0455 Code?

While many trouble codes have several noticeable symptoms, for some, an activated check engine light may be the only indication. As for the P0455 trouble code, you may notice the following symptoms:

• Check Engine Light is on
• Possible fuel smell (rather uncommon)

How to Diagnose the P0455 Code

When trying to diagnose a P0455 code, the first thing a layperson should do is make sure the gas cap is on tight. A loose or faulty gas cap can easily trigger the code. If tightening the gas cap doesn’t work, you may want to try purchasing and installing a new gas cap, since doing so is cheap and easy.

Keep in mind: once you’ve tightened or replaced the gas cap, you’ll have to clear the code with a code reader or scan tool afterward. The code won’t immediately go away on its own.

If the gas cap doesn’t solve the problem, you’ll need to dig further. There are numerous potential causes for OBD-II code P0455. As such, diagnosis can be difficult. For an idea of how to troubleshoot the code, check out the videos below:

How to Fix the P0455 Code

Disclaimer: Due to the wide variability in vehicle makes and models, as well as other factors, the following information must not be construed as complete or the only definitive way to address a particular issue. Instead, the following content merely attempts to give you a better idea of what a do-it-yourself approach to the issue might involve. You are encouraged to find more technical resources regarding the subject or take your vehicle to a professional technician for the best results.

Pro Tip: Newer systems check the EVAP system for leaks. If they find no leak and then notice the fuel level has changed followed by a large leak, logic dictates that you left your fuel cap off. Some vehicles actually have a special warning light on the instrument cluster for this.

Before attempting to fix a P0455 trouble code, you might want to check for potential technical service bulletins (TSBs) and recalls first. Having said that, you won’t typically find any TSBs related to code P0455.

Vehicle manufacturers issue TSBs to notify dealerships and technicians about an issue surrounding a specific model, and they also include the steps on how to resolve the problem. But remember, just because there’s a published TSB, it doesn’t mean the concern will be repaired free of charge unless the vehicle is still under warranty.

Many aftermarket companies also republish these TSBs for independent technicians and auto repair shops.

You can check TSBs on your own using authoritative sites from organizations like the National Highway Traffic Safety Administration (NHTSA) and Environmental Protection Agency (EPA). You’ll need to enter your vehicle’s identification number in the search bar to check for make-model information.

If there aren’t any recalls or TSBs about your vehicle, here are some alternative solutions to resolve the code. 

Inspect the Gas Cap

The first thing you can try is to inspect the gas cap. Dirt or grime buildup might prevent it from sealing properly, and spraying WD-40 might do the trick.

But if you notice some cracks along the gas cap, it might be time to replace it with a new one to prevent any leaks.

If you’re seeing DTC P0455 on your Hyundai vehicle, check the gas cap’s sealing area. The cap’s gasket might have shrunk or the fuel filler neck might have sprung a leak. Greasing the gasket could help. Also make sure that when you close the cap, it clicks into place.

If the gas cap isn’t the problem, the next thing you should check is the EVAP system.

Test the EVAP System for Leaks

To test the system for leaks, it should be pressurized to a level below 1 PSI. The system is usually pressurized with nitrogen through a special regulator from a special machine.

If the pressure falls below the normal range, it’s confirmed that there is indeed a leak in the system. A large leak is usually easy to find unless it’s hidden inside the canister purge or vent valves.

There are two primary ways to check for leaks in the EVAP system beyond a good visual inspection.

The first one is via smoke machine testing, which involves introducing smoke under low pressure from a machine.

The other method is nitrogen gas pressurization, which introduces gas in the fuel system. The service technician typically uses amplified headphones to listen for leaking air.

Note that you probably won’t have the ability to do either of these because you don’t have the equipment. Most shops use a smoke machine that puts pressurized smoke in the system, which will exit at the point of the leak for visual detection.

Check the Canister Purge and Vent Valves

Check the canister purge and vent valves. The canister purge valve is normally closed, and the PCM only opens this during purging.

Meanwhile, the canister vent valve is normally open and the PCM only closes it whenever EVAP leak testing is under way. Further, the PCM won’t do a leak test if the fuel level is above 85% or below 15%, so you could have a leak and not see a code if you run your tank near empty or nearly full all the time.

The canister purge valve is linked to the intake manifold vacuum using a rubber hose, drawing gasoline vapors from the charcoal canister into the engine when it’s open. The canister vent valve is connected to the canister air inlet.

To test the canister purge valve, make sure that the engine is turned on. This is usually placed behind the intake and beside the throttle body.

Once you’ve located the valve, place a finger in the vacuum port and check for suction. If you feel that your finger is being sucked into the valve, it means that it’s stuck and should be replaced.

The Bottomline

Always keep in mind that resolving trouble codes on your own comes with risks, especially if you’re not well-versed in automotive repair. Of course if all you need to do is replace the gas cap, well, you can handle that with ease.

Performing the repair procedure incorrectly can lead to further complications and might even result in a more expensive repair bill. So if you’re not confident in your DIY skills yet, it’s best to leave the job to the pros instead.

But if you think you can handle the job on your own, make sure to have the right tools and information before proceeding.

Other Notes About Code P0455

Aside from the symptoms listed above (i.e., activated check engine light and slight fuel smell), there may be no other noticeable symptoms for the P0455 trouble code. As such, this code may not be considered severe. Note that fuel economy issues may arise as a result of fuel vapor leaks. And so, like other diagnostic trouble codes, P0455 should be addressed immediately to avoid potential fuel mileage problems and other complications concerning the emission control system and other vehicle components.

Also, an evaporative emission control system leak doesn’t only pollute the air while the vehicle is running. Harmful evaporative emissions can be released into the atmosphere 24/7 from a hole as small as a pinprick. This is why it’s important to consult a licensed mechanic when faced with a P0455 engine code as soon as you have ruled out a gas cap issue.

There are other diagnostic trouble codes related to code P0455. These include P0450, P0451, P0452, P0453, P0454, P0456, P0457, P0458, and P0459.

Shopping for Fuel System Repairs

If your vehicle logs a P0455 code, then it’s time to consult a mechanic and replace faulty fuel system components as advised. Whether you need a new gas cap or a fuel tank pressure sensor, CarParts.com can make shopping for replacement parts quick and hassle-free.

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Products Mentioned in this Guide

Vapor Canister Purge Valve Gas Cap Fuel Tank Fuel Tank Pressure Sensor