P0457 Code: Evaporative Emission System Leak Detected (Fuel Cap Loose/Off)

If your OBD-II scanner indicates a code P0457, address the issue with the help of this comprehensive guide.

What Does the P0457 Code Mean?

Diagnostic trouble code (DTC) P0457 stands for “Evaporative Emission System Leak Detected (Fuel Cap Loose/Off).” The code indicates that your car’s primary computer, which is often referred to as the powertrain control module (PCM), has detected a large leak in the EVAP system. This leak is often caused by a loose or missing fuel cap.

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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. Typically when you see a P0457 code it means the ECM/PCM has noticed a higher fuel level and a new leak. Check the fuel cap first if you get this code.

Note: Although code P0457 is a generic code specified by the Society of Automotive Engineers (SAE), the code’s definition may be different depending on the vehicle manufacturer.

Related codes include P0455 and P0456, which indicate minor and moderate EVAP leaks, respectively.

What Does the EVAP System Do?

The evaporative emission control system (EVAP) keeps fuel vapor from escaping into the atmosphere.

A typical EVAP system features the following primary components:

• The fuel tank
• The gas cap
• A pressure sensor that measures the pressure in the fuel tank
• A charcoal canister that captures the fuel vapor
• A purge valve
• A vent valve that closes during system testing
• Hoses and lines that connect the system together

The focal point of the EVAP system is the charcoal canister—a component that stores the fuel vapors when the engine is off.

When the engine is running and conditions are correct, the PCM opens a device called the purge valve. This allows the vapors to be drawn into the engine, where they are burned as part of the normal combustion process.

Vehicles built after 1996 have what’s referred to as an “enhanced evaporative emissions control system.” With this design, the PCM can test the EVAP system for both purge flow and system leakage. When the module detects a leak, it issues a diagnostic trouble code.

A loose gas cap is one potential source of an EVAP system leak. If the cap does not seal properly against the filler neck, fuel vapors will escape into the atmosphere.

Many vehicles can check whether refueling has taken place by monitoring parameters, such as the ignition switch and fuel level. If the PCM detects an EVAP system leak shortly after refueling, it assumes the gas cap was left loose and sets code P0457.

The code can also be triggered by a large leak somewhere else in the EVAP system.

What are the Possible Causes of the P0457 Code?

The PCM issues a code P0457 in response to a large leak in the EVAP. Fuel vapor can escape from the system in several ways:

• Gas cap is cracked, loose, or got dislodged and went missing
• Dirt and foreign objects on the gas cap’s threading broke the seal
• Exposure to the elements or sheer age eroded the hose’s material, causing it to crack, loosen, or rot
• Damaged fuel filler neck
• A leak somewhere else in the EVAP system

What are the Common Symptoms of the P0457 Code?

Typically, the only symptom associated with code P0457 is an illuminated check engine light. You may also smell fuel.

Note: If there are other codes stored in addition to P0457, the causes and symptoms may differ from those listed here.

How to Diagnose the P0457 Code

If you encounter code P0457, the first thing you want to do is tighten the gas cap, clear the code with a scan tool or code reader, and see if it returns. You may need to replace the gas cap if it’s damaged or not forming a good seal.

In most cases, tightening or replacing the gas cap will solve the problem. However, it’s possible for a leak somewhere else in the EVAP system to trigger code P0457. If that is the case, you’ll need to do some troubleshooting.

Here are a couple of videos to give you an idea of what the diagnostic process may entail:

How to Fix the P0457 Code

As was mentioned, you may be able to get rid of code P0457 by simply tightening or replacing the gas cap. But if that doesn’t help, you’ll need to do some troubleshooting (or have a professional do the troubleshooting for you) to determine the cause of the EVAP leak.

Keep in mind that all vehicles are different. For example, the solution to a P0457 code in a Ford may not be entirely the same as the fix for a P0457 in a Subaru. When troubleshooting and repairing diagnostic trouble codes, make sure to consult the factory repair information for your application.

Repair manuals, such as those from Chilton, are useful, but an ALLDATA subscription is even better. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information.

Where to Get a New Gas Cap to Clear the P0457Code

Driving around with a set P0457 code is not a good idea. While the only symptoms are an illuminated check engine light and the smell of fuel, they could be precursors to other issues. As such, it’s best to deal with the problem directly. If you’ve determined that getting a new gas cap will clear the code, you can find what you need in no time at CarParts.com.

Thanks to your strategically located warehouses across the country, you can get your new gas cap delivered to your doorstep in as fast as two business days if you order before noon. On top of that, all our products come with a low-price and lifetime replacement guarantee to give you the best value for your money.

It’s also easy to find a compatible gas cap replacement using our vehicle selector. Input your car’s year, make, and model to narrow down the catalog to direct-fit caps. Use our search filters to show the list based on your preferred brand, price range, quantity, and more.

Check out our catalog and get the best deals on gas caps today!

Products Mentioned in this Guide

Gas Cap Fuel Tank Fuel Pressure Sensor Purge Valve Fuel Tank Vent Valve