P0456 – Meaning, Causes, Symptoms, & Fixes
Code P0456 Definition
Evaporative emission control system leak (small).
Code P0456 Meaning
The evaporative emission control (EVAP) system prevents fuel vapors from escaping into the atmosphere. The fuel vapors from the fuel tank are absorbed and stored by charcoal pellets in the charcoal canister. The vent control valve is controlled by the engine control module (ECM) and allows air to flow into the charcoal canister to purge the gas vapors into the engine air intake to be burned. The flow of the gas vapors from the charcoal canister to the engine air intake is controlled by a purge volume control valve. The vent control valve is usually open when the engine is at normal operating temperature, and the purge volume control valve is commanded on when the ECM is ready to burn the built-up fuel vapors. However, when the vehicle is turned off the ECM performs a leak test to ensure the evaporative emission control system is working properly. During the leak test, the ECM closes the vent control valve and purge valve to seal the evaporative system. If the EVAP system does not maintain the pressure, the ECM recognizes an evaporative emission control leak. In the case of P0456, it is a small-sized leak, smaller than .020” in diameter.
What Are the Symptoms of Code P0456?
- Check Engine Light is on
- Decreased fuel economy
- Increased vehicle emissions
- Fuel smell
What Is the Cause of Code P0456?
- Loose or damaged gas cap
- Leaking or disconnected EVAP hose
- Faulty purge volume control valve
- Faulty canister vent control valve
- Charcoal canister leak
- Leaking fuel tank
What Is the Severity of Code P0456?- Low
It is unlikely the driver will notice any symptoms with check engine light code P0456 other than a slight odor of fuel, a slight decrease in fuel economy, and the check engine light. However, as with all check engine lights, it is recommended that you get it fixed as soon as possible so the engine can be running at the proper specifications to prevent further damage.
Code P0456 Common Diagnosis Mistakes
Many assume that a loose fuel cap is the only problem and does not perform all the tests necessary to diagnose the full EVAP system. The P0456 small leak is a bit trickier to diagnose. Also, many manufacturers have technical service bulletins regarding EVAP codes. Be sure to check if your vehicle has any technical service bulletins available to save time diagnosing and or misdiagnosing the car.
Tools Needed to Diagnose P0456:
- Fused power wire
- Ground wire
How To Diagnose P0456:
- Scan your vehicle to verify P0456 is the only code present. If other codes are present regarding fuel pressure or the fuel system, repair and diagnose those first. If it is paired with P0441, P0440, and/or P0446, there is most likely a solenoid failure, leaking charcoal canister, or a more complex EVAP leak.
- Inspect your gas cap to see if it is loose or damaged. If your gas cap is loose, tighten it and clear the code. Inspect your gas cap for physical damage or deterioration. However, it should be noted that damage to the gas cap or deterioration of its components is not always noticeable. If your gas cap was not loose and you do not see any indications of failure, try replacing the gas cap anyway and clearing the codes. Gas caps are relatively inexpensive and are often the fix for code P0456.
- Check for cracked or disconnected EVAP hoses near or connected to the engine air box. Replace cracked/disconnected hoses. Clear code
- Inspect the fuel tank and charcoal canister for damage and leaks. Replace if necessary.
- Check the purge volume control valve for proper operation. This valve is normally not powered on and when at rest, with no power source applied, does not allow air to pass through. It can get sticky causing leaks. To test: Remove hoses from either side of the purge volume control valve with the key and engine off. Blow through openings with no power supplied. If you can’t blow through them, they are sealing properly and are most likely not the cause of this small evap leak. (Tech Tip- The purge volume control valve is usually under the hood near the airbox or intake manifold.)
- Check the charcoal canister vent control valve for proper operation. This valve is normally not powered on and when at rest, with no power source applied, allows air to pass through. It can get sticky, causing leaks, or the internal solenoid can fail and not operate properly. To test: Remove hoses from either side of the charcoal canister vent control valve with the key and engine off, unplug it from the vehicle, and remove it from the vehicle. Blow through openings with no power supplied. Air should pass through. Now supply a fused power source to one side and ground to the other of the electrical connector. Blow through the openings again. If you can’t blow through them, they are sealing properly and are most likely not the cause of this small evap leak. (Tech Tip- The charcoal canister vent control valve is usually connected to the charcoal canister underneath the vehicle.)
- The leak causing code P0456 is often too small to see. If you have completed all of these diagnostic steps, a smoke test may be necessary. You can purchase a smoke tester from Amazon to do it yourself, or you may want to take it to a shop to find the leak.
Estimated Cost of Repair
For error code P0456, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.
- Gas Cap $20-$60
- Evap Purge Volume Control Valve $150-$200
- Charcoal Canister Vent Control Valve $150-$200
- Replacement Evap Line $50-$100
- Charcoal Canister $200-$600
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