#OBD Codes

P0456 – Evaporative emission control system very small leak detected

P0456 – Evaporative emission control system very small leak detected
Back to OBD codes library

Technical definition     

EVAP emission control system (very small leak). Leak detected. 

What does P0456 mean?

Trouble code P0456 indicates a very small leak in the evaporative emission control system (also known as EVAP). This system reduces air pollution by preventing fuel vapors from escaping from the gas tank into the atmosphere. It traps vapors in a charcoal canister until the engine can burn them. 
The engine control unit (ECU) performs periodic tests to ensure that the EVAP system is working properly. If ECU detects a leak, it triggers a trouble code and turns on the check engine light.
This code usually indicates a minor problem such as a loose gas cap, damaged vapor lines, a faulty canister purge valve, or a small crack in the fuel tank.
Diagnostic trouble code P0456 often appears with other EVAP-related codes. These may include P0440 (EVAP system malfunction), P0441 (improper purge flow), or P0442 (EVAP system small leak detected). Multiple codes can help pinpoint the exact problem. 

How serious is P0456?

The P0456 code isn't worth stressing about. It can increase air pollution by releasing fuel vapors into the atmosphere and will turn on the check engine light, but it won't affect your vehicle's performance immediately. Fixing it is also relatively inexpensive. 

Can I still drive with P0456?

Yes, you can still drive with a P0456 fault code, yet you should address the problem soon. Driving with a very small evaporative emission system leak won't cause immediate damage to the car. However, it can lead to other problems if you leave it unfixed.
If you keep driving without fixing this issue, the check engine light will stay on. If you ignore it, you might not notice when a new engine problem happens.
In addition, fuel vapors are not only harmful to the environment, but also to your health. Prolonged exposure to these vapors can cause headaches, respiratory issues, and other health problems.

Symptoms of P0456

If your car has a P0456 code, you may not notice any changes in vehicle performance, but some symptoms may appear. The most common sign is the check engine light.
If the leak gets bigger over time, you may also smell fuel near or inside your car. 

Common causes of P0456 

Several issues can cause the P0456 code. The most common is a loose or broken fuel cap. When the cap doesn't seal properly, it allows fuel vapors to escape and trigger the code. 
Another common issue arises from cracked or damaged EVAP hoses, which carry fuel vapors to the charcoal canister. 
A faulty EVAP purge or vent valve can also lead to this code.  
The fuel tank itself may have a small crack or damage. This is less common and can happen due to wear and tear or minor accidents. 
Finally, a malfunctioning leak detection pump can be the culprit. This pump helps the ECU detect leaks in the EVAP system. If it fails, it may incorrectly indicate a leak and trigger the P0456 code. 

How to troubleshoot P0456

Use these tips to accurately diagnose and fix a P0456 code:
Scan for other codes 
Use a diagnostic scanner to check for other related trouble codes. These may provide additional clues to the underlying issue. P0440-P0455 codes indicate problems related to the EVAP system. 
Clear the code and test drive 
Use the OBD2 reader to clear the trouble codes. Then drive your car for a day. 
After the drive, scan the car to see if the same problem reappears. If not, it might've just been a one-time occurrence. But if the issue is here again, it means there's a real problem that needs further action.
Check the gas cap and seals 
Make sure the gas cap is tight and undamaged. Check the condition of the rubber O-ring and replace it if necessary. A loose or damaged gas cap is the most common cause of code P0456. 
Use a smoke machine
A smoke test can help locate small EVAP leaks by filling the system with smoke and observing where it exits. This method is very effective for small leaks. 
Inspect EVAP hoses
Check for cracks, holes, or disconnected hoses. Replace any damaged ones. 
Examine the fuel tank
Inspect the fuel tank for signs of damage or leaks. If necessary, repair or replace the tank. A cracked fuel tank can leak fuel vapor and cause fire.
Check the leak detection pump
Ensure that the evaporative emission system leak detection pump is working properly. If it's defective, it might incorrectly detect a leak. Replace the pump if necessary so you can detect leaks accurately.


How does a faulty gas cap cause a P0456 code? 
A defective or loose gas cap can prevent the EVAP system from sealing properly. This allows fuel vapors to escape, triggering a P0456 code. It's one of the easiest things to fix. 
The gas cap is a key component of the EVAP system. It must create a tight seal to keep fuel vapors contained. A damaged or improperly seated gas cap will disrupt this seal.
What are the risks of ignoring the P0456 code for a long period?
Ignoring the P0456 code can result in a failed vehicle inspection and fines. 
Over time, a small EVAP leak can become larger. This can cause a stronger fuel odor outside and inside the car.
Disclaimer: Advice, how-to guides, and car care tips on our blog are intended as helpful resources for general maintenance and repairs. While we strive for accuracy, the information is provided to the best of our knowledge and should be used at your own discretion and risk.

Always refer to your vehicle's owner's manual or consult a certified mechanic for specific repair details and safety procedures.