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Looking for information on how you have fixed this error code on your Mini CooperS 2014. Have already reseated the gas cap. Didn't turn off the Check engine light..
Faulty purge valve
Faulty canister vent valve
Charcoal canister leak
Leaking fuel tank
Code P0456 Common Diagnosis Mistakes
Many assume that a loose fuel cap is the only problem and do not perform all the tests necessary to diagnose the full EVAP system. The P0456 small leak is a bit trickier to diagnose. Also, many manufactures 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.

Code P0456 Diagnosis Steps
Tools Needed to Diagnose:
FIXD
Digital multimeter
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 are not always noticeable. If your gas cap was not loose and you do not see any indications of failure, try replacing the gas cap anyways 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 engine air box
Replace cracked/disconnected hoses
Clear code
Inspect the fuel tank and charcoal canister for damage and leaks. Replace if necessary.
Check both the charcoal canister vent valve and purge valve for proper operation. These valves can get sticky causing leaks or the internal solenoid can fail and not operate. To test:
Disconnect the valve connector and test that the valve is receiving power with a multimeter
If there is no power, there is most likely a wiring problem or a faulty powertrain control module.
Tech Tip- The canister vent valve is usually located under the car in the rear of vehicle by or attached to the charcoal canister. The purge valves are usually under the hood near the airbox or intake manifold.
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.
good dealer level diagnostics scan might help, autocom or wurth snooper good value
 
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