P0457 OBD-II: Evaporative Emission System Leak Detected (fuel cap loose/off)

What does code P0457 mean?

Code P0457 stands for Evaporative Emission System Leak Detected (Fuel Cap Loose/Off).

The evaporative emissions (EVAP) system is designed to prevent hydrocarbons (fuel vapors) from escaping into atmosphere. When hydrocarbons mix with sunlight and nitrogen oxides they form smog. To prevent this, the EVAP system stores the hydrocarbons in a canister. Then, when the time is right, the hydrocarbons are pulled into the engine and burned.

The main parts of the EVAP system are as follows:

• The charcoal canister. As the name implies, the charcoal canister contains charcoal which absorbs and stores the fuel vapors. When the time comes to "purge" the vapors, fresh air passes over the charcoal. This releases the vapors.
• Purge solenoid and valve. When engine operating conditions are correct, the purge solenoid opens the purge valve. This allows fuel vapors to be sucked into the engine and burned.
• Canister vent solenoid and valve. Enhanced EVAP systems use a canister vent solenoid and valve during system self-testing. The PCM closes the valve, sealing the canister off from outside air. Then, the powertrain control module (PCM) can monitor the closed system and check for leaks.
• Fill control tube. This tube is used to shut off the service station pump after refueling.
• Gas cap. The gas cap contains a vent valve. This device releases fuel system pressure in the event of a malfunction.

Once the engine is shut down, the PCM closes off the EVAP system and checks for leaks. A leak at any part of the EVAP system, including the gas cap, can set a diagnostic trouble code. Code P0457 indicates the PCM has detected an EVAP leak, most likely caused by the gas cap.

EVAP system

P0457 Symptoms

• An illuminated check engine light

Common causes for P0457

Code P0457 is typically caused by one of the following:

• A loose or faulty gas cap
• A leaking EVAP hose
• A problem with the purge valve or vent valve

Get it diagnosed by a professional

Find a shop in your area

How to diagnose and repair code P0457

Check the gas cap and replace as needed

The first thing to check is the gas cap. Even if the cap seems secure, it may not be sealing properly. Gas caps are inexpensive, so if you have any doubt, replace the cap. Most of the time, this code is caused by gas cap issues.

Gas cap / Image source

Note: It may take a while for the check engine light to go out once the cap is replaced, since the EVAP system is not always monitored by the PCM. You can either drive the vehicle until the light goes out, which might take a very long time. Or you can turn it off with a diagnostic scan tool/code reader.

Perform a preliminary inspection

If the gas cap doesn’t do the trick, a visual inspection of the EVAP system should be performed. A trained eye can look for broken hoses or visibly damaged components. If a problem is found, the issue should be repaired and the code cleared. If nothing is discovered, the next step is to check for technical service bulletins (TSBs). TSBs are recommended diagnostic and repair procedures put out by the vehicle manufacturer. Finding a related TSB can greatly reduce diagnostic time.

Check for leaks

Without the proper equipment, finding an EVAP leak can be extremely difficult. Technicians typically use smoke machines to pinpoint the problem, as outlined below.

• To begin an EVAP smoke test, the technician closes off the EVAP system. This simulates the way the PCM closes the system during self-testing.
• Then, the smoke machine is connected to the EVAP system through a port in the engine compartment.
• After the machine is turned on, smoke travels through the system and billows out at the point of the leak. Once the leak has been identified, it can be repaired.

Test the purge valve and vent valve

Typically, a problem with the purge or vent valve will result in additional code being set, not just P0457. However, if no problems were found up to this point, it’s a good idea to test the valves. The EVAP system is not sealed unless the purge valve and vent valve are completely closed. A trained professional will test the valves by closing them and seeing if they hold vacuum.

• A trained professional starts the test by closing the valve. This can be done either by jumping the valve solenoid to power and ground, or by closing the valve with a diagnostic scan tool. Note: some systems use solenoids that are normally closed, while others use solenoids that are normally open. This must be determined prior to testing.
• Next, a handheld vacuum gauge is attached to the valve and vacuum is applied. The vacuum reading should hold steady with the valve in the closed position. It should drop when the valve is opened.

Other diagnostic codes related to P0457

• P0455: Code P0455 indicates the PCM has detected a large EVAP system leak.
• P0456: Code P0456 indicates the PCM has detected a small EVAP system leak.

Code P0457 technical details

The EVAP monitor is non-continuous. This means the system is only tested and monitored under certain conditions. For code P0457 to be set, the ignition must be off, the fuel must be at a certain level and ambient temperature must be within a pre-defined range.