P0456 OBD-II Trouble Code: Evaporative Emissions System Small Leak Detected

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Cost of diagnosing the P0456 code

P0456 is a diagnostic trouble code (DTC) for "Evaporative Emissions System Small Leak Detected". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $70.00. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $30.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
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P0456 code definition

Evaporative Emissions System Small Leak Detected

What the P0456 code means

P0456 is an OBD-II generic code that the engine control module (ECM) has detected a very small leak in the evaporative system during the vehicle off testing. The test has to fail twice in a row to cause the code to be activated by the ECM.

What causes the P0456 code?

  • The ECM has commanded the purge control valve to close the system and activates the evaporative vacuum pump to bring the system into a small amount of specified vacuum and then monitors the system for leaks. If the system detects a very small leak during the test then the ECM stores the code and waits till a second test can be done and if that test detects a very small leak then the ECM stores the code P0456 and turns on the check engine light.

  • The cause of code P0456 can be a small leak at any of the system components or hose connections.

  • The two most common causes of the code is the gas cap vent and the purge vent valve will not seal completely.

What are the symptoms of the P0456 code?

The Check Engine Light will be illuminated and the code is set in ECM memory.

How does a mechanic diagnose the P0456 code?

  • Scans codes and documents the code in the ECM, views the freeze frame data to see when fault happened

  • Inspects the entire vapor purge valve system to include the purge valve and vent valve hose connectors for damaged or loose connections

  • Checks the purge valve vent for any blockage from dirt, debris or spider webs that could cause the valve to not be able to complete a total seal of the vapors

  • Performs a smoke leakage test on the fuel vapor system to try and locate the cause of the vapor leak using the test vapor port, checks the fuel cap for vent leakage

  • Checks the purge control valve to see if it will hold a vacuum when activated

Common mistakes when diagnosing the P0456 code

  • Not checking and assuming the purge control valve is defective without doing a thorough diagnostics of the complete system to later find the wiring is broken or cut

  • Not verifying the leak and replacing parts that may or may not be the problem

  • Not checking for any technical service bulletins that may have a fix for the code

How serious is the P0456 code?

  • Code P0456 causes the Check Engine Light to go on and this alone will cause a failed emission test.

  • The code means the fuel vapor system has a very small leak and may be hard to locate on some vehicles and the code will keep coming back till the leak is found.

  • The ECM monitors will not pass emissions if the leak is not found and just the Check Engine Light is turned off.

What repairs can fix the P0456 code?

  • Replacing a leaking gas cap
  • Replacing the leaking or clogged purge vent valve
  • Replacing a leaking purge valve

Additional comments for consideration regarding the P0456 code

Code P0456 is not a common code for most vehicles and some manufacturers do not use the code at all. Vehicles that come in with the Check Engine Light on with this code the most common cause is the fuel cap or the purge control valve or the vent valve will not hold in the vapors completely and have very small leaks that are detected.

Need help with a P0456 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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