P0456 Code: Meaning, Causes, and Symptoms | OBD2 Codes

P0456 – EVAP Control System Leak Detected Very Small Leak

P0456: What does it mean?

The Codes P0456 indicates that a very small leak is detected in the Evaporative Emission Control System(EVAP).

The EVAP is a system designed to keep gasoline vapor from leaking. It’s part of the Powertrain Control Module(PCM) and may notify a Code P0456 when a very small leak was detected.

Similar Codes include P0455 (EVAP control system leak detected large leak) and P0442 (EVAP control system leak detected small leak). All three codes have similar possible symptoms and causes, as well as simple fixes. But as the leak is minor, P0456 and P0442 are harder to diagnose, as you cannot see clearly cracked hoses or connectors. 

Severity: Low

Not important, as you cannot see a decrease in fuel efficiency. But you should address it as you cannot pass the emission test with P0456 present.

Difficulty of diagnosis or repair: 3 out of 5

P0456 Possible Symptoms

As it’s a very small leak, P0456 will not always show itself except the engine light/service engine soon warning light on. Sometimes, you may notice a small fuel odor caused by the leak.

  • Engine Light ON (or Service Engine Soon Warning Light)
  • Possible a noticeable fuel odor caused by the release of fuel vapors

P0456: Possible Causes

There are many possible causes for the code P0456, including:

  • Missing or loose fuel cap
  • Incorrect fuel filler cap used
  • Fuel filler cap remains open or fails to close
  • Foreign matter caught in fuel filler cap
  • Evaporative Emission (EVAP) canister or fuel tank leaks
  • Evaporative Emission (EVAP) system hose leaking
  • Fuel tank leaking

Possible Checks/Fixes you can do yourself:

When you see a DTC Code P0456, there’re several checks you can do:

  1. Check the code from your OBD2 Scanner / Car Code Scanner and verify that it’s the only code present. If other codes are on the list, they should be checked first.
  2. If you have other codes such as P0441or P0440, the issue might be a solenoid failure or a more complex system leak. Address these issues first.
  3. If Code P0456 is the only code present, check your gas cap to see if it’s open or loose. Tighten your gas cap. 
  4. After you tighten the gas cap, the engine light may turn off after several drive cycles. Refer to this article about the drive cycle. It will be completed mostly after a normal day drive.
  5. If the engine light doesn’t go off, inspect your gas cap for physical damage or deterioration. It’s not always noticeable, you can try to replace your gas cap as it’s not expensive. It usually will clear the codes P0456.
  6. If the fuel cap didn’t fix it, you can check for aged, cracked or disconnected hoses of the EVAP near or connected to the engine air box. This is a common problem for old cars because of aged rubber hoses and dry-out gaskets. Replace the hoses and clear the code.
  7. If a replaced hose doesn’t solve the problem and the code comes back again, you should consider performing an EVAP system leak check. You can do it in most repair shops and car dealers. They will usually perform a smoke check through your EVAP and the smoke will show if there’s any leak from any hoses or seals. 

How much is the cost to clear P0456?

For car code P0456, several repairs may apply, and the cost estimations are below:

  • Replace the Gas Cap: $20-$60
  • EVAP Line: $20-$100
  • EVAP Vent Control Valve: $150-$200
  • Purge Volume Control Valve: $150-$200
  • Charcoal Canister Vent Control Valve $150-$200