Troubleshooting Code P0457 in Your Subaru: A Step-by-Step Guide to Fixing Evaporative Emissions System Issues

As a Subaru owner or mechanic, it can be frustrating to see the check engine light turn on. One common issue that may trigger it is code P0457. While it may seem daunting, fixing this issue is usually straightforward with the right tools and knowledge.

What is Code P0457 and What Causes It?

Code P0457 is an OBD-II diagnostic code that indicates a problem in the evaporative emissions system. This system ensures that fuel vapors don’t escape into the atmosphere by storing them in a charcoal canister and then routing them back to the engine to burn off. Code P0457 occurs when the system detects a leak that is larger than a specified amount.

There are several reasons why this issue may occur. One of the most common culprits is a loose or damaged gas cap, which can cause fuel vapors to escape and trigger the code. Another potential cause is a faulty canister vent valve, which may allow fuel vapors to leak out. The fuel tank pressure sensor may also be to blame if it is sending incorrect readings.

Symptoms of the Issue

The main symptom of code P0457 is the check engine light turning on. However, there may be other indications of a problem, such as the smell of fuel near the vehicle. If the issue goes unnoticed for too long, it may also cause a decrease in fuel efficiency.

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Steps to Diagnose Code P0457

The first step in diagnosing code P0457 is to use an OBD-II scanner to read the code. This can be done by plugging the scanner into the vehicle’s OBD-II port, which is usually located under the dashboard on the driver’s side.

Once the code is read, you can begin checking for potential causes. Start by inspecting the gas cap to ensure that it is tightened properly. If it is loose or damaged, replace it and clear the code to see if the issue is resolved. If the gas cap is not the problem, move on to checking the canister vent valve and fuel tank pressure sensor.

To test the canister vent valve, you can use a multimeter to check its resistance. If the valve does not have any resistance, it is likely faulty and should be replaced. To test the fuel tank pressure sensor, you can use a vacuum pump to apply pressure to the sensor. If the sensor does not respond correctly, it may need to be replaced.

Possible Solutions to Fix Code P0457

If the issue is caused by a loose or damaged gas cap, simply replacing it may resolve the issue. If the issue is caused by a faulty canister vent valve or fuel tank pressure sensor, replacement is also recommended. These parts are relatively inexpensive and easy to replace, even for those with limited mechanical experience.

If none of these solutions fix the issue, it may be necessary to perform a smoke test to locate any other potential leaks in the system. This involves introducing smoke into the system and looking for where it escapes. A mechanic may be needed to perform this test.

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Tips for Preventing the Issue in the Future

The best way to prevent code P0457 from occurring in the future is to ensure that the gas cap is always tightened properly after filling up. Additionally, regular maintenance of the evaporative emissions system can help catch potential issues before they become larger problems.

Frequently Asked Questions

Is it safe to drive with code P0457?

While it may be safe to drive with code P0457, it is still recommended to address the issue promptly to avoid any potential decrease in fuel efficiency.

Can code P0457 go away on its own?

No, code P0457 will not go away on its own and must be addressed to turn off the check engine light.

Can I replace the canister vent valve or fuel tank pressure sensor myself?

Yes, these parts are relatively easy to replace and can often be done by those with limited mechanical experience.


Code P0457 in your Subaru can be a frustrating issue, but with the right tools and knowledge, it is usually easy to fix. By following the steps outlined in this guide, you can diagnose and repair the issue yourself or with the help of a mechanic. Remember to also take preventative measures to avoid future issues with the evaporative emissions system and keep your Subaru running smoothly.

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Billy Covington

With a passion for all things automotive, Billy is our go-to expert on Subaru performance upgrades and modifications. He's been featured in several car magazines and blogs, and his extensive knowledge and expertise make him a valuable member of our team. When he's not working on cars, he enjoys playing guitar and writing music.

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