OBD-II Trouble Codes

P0455 Code: Evaporative Emission System Large Leak Detected

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If the Check Engine Light is illuminated and it’s triggering a P0455 code on your OBD-II scan tool, you may be looking at a gas cap issue. But that’s certainly not the only reason why your scanner could be displaying a P0455.

Read on to learn more about this trouble code.

What Does the P0455 Code Mean?

Diagnostic trouble code (DTC) P0455 stands for evaporative emission 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.

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.

vehicle gas cap left open
A gas cap left open is one of the possible causes of P0455 Code.

Basic (non-enhanced) EVAP systems were first introduced in the1970s. 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 car’s computer controls both the purge and vent valves via electronic solenoids. The computer also monitors EVAP system operation, checking for leaks and other issues.

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 trouble code:

What are the Common Symptoms of the P0455 Code?

You may notice the following symptoms if you drive a vehicle with a P0455 trouble code:

check engine light of a car illuminating
The check engine light should illuminate when you get code P0455.

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 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

As mentioned, there are multiple possible reasons why code P0455 gets activated in your car, which means the only way to fix the issue is to look for the parts that are contributing to the problem and either repair or replace them. If your gas cap was left open, secure it, and see if that fixes the issue.

Keep in mind that all vehicles are different, so it’s extremely important that you only follow factory repair information for your application. It’s best to have a mechanic work on advanced repairs, but if you want to fix the code yourself, you may consider getting a repair manual, such as Chilton or ALLDATA to get detailed repair information.

Other Notes About Code P0455

An evaporative emission system leak doesn’t only pollute while the vehicle is running. Harmful evaporative emissions can be released into the air 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.

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In the Garage with CarParts.com is an online blog dedicated to bringing DIYers and devoted car enthusiasts up to date with topical automotive news and lifestyle content. Our writers live and breathe automotive, taking the guess work out of car repairs with how-to content that helps owners get back on the road and keep driving.

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