Is your check engine light illuminated? Does your vehicle smell of fuel? Your fuel cap may either be loose or missing. If your OBD-II scanner indicates a code P0457, address the issue with 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.
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.