Categories: Trouble Codes

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

P0456 code definition

Evaporative Emissions System Small Leak Detected

What Does the P0456 Code Mean?

P0456 is an generic powertrain code, applying only to OBD-II vehicles, that the Powertrain Control Module (PCM) has detected a lack of pressure at the Fuel Tank Pressure (FTP) sensor within the EVAP system indicating a small leak.  The test must fail twice in a row to cause the code to be thrown by the PCM.

What Causes the P0456 Code?

  • The PCM indicates to the purge control valve to close the system and activate the evaporative vacuum pump to bring the system into a state of vacuum and then measures the system for leaks. If the system detects a any loss of pressure in the vacuum during the test the PCM will store the code and wait until a second test can be done.  If the subsequent test also detects a leak, the ECM will store the code P0456 and activate the maintenance indicator/check engine light.
  • The cause of code P0456 is typically a leak within the system components or hose connections.
  • The most common causes of the P0456 code are the gas cap vent and the purge vent valve not completely sealing.

What are the Symptoms of the P0456 Code?

Since emissions is a closed system, you may not notice any symptoms other than the Maintenance Indicator or Check Engine Light will be illuminated on the dashboard.  When using an OBD Reader, the P0456 code is set in ECM memory.

How to Diagnose the P0456 Code

  • Scan and document codes in the PCM using an OBD-II Scanner.  Then, view the freeze-frame data for information around when the fault occurred.
  • Inspect the vapor purge valve system including the purge valve and vent valve hoses and connectors for damaged or loose connections.
  • Check the purge valve for any debris that could cause blockage within the valve preventing a complete seal of the vapors.
  • Perform a leakage test on the fuel vapor system.  Try to determine the location of the vapor leak using the test vapor port.  Then also check the fuel cap for vent leakage.
  • Finally, check the purge control valve to see if it will hold a vacuum when activated

Common Mistakes Diagnosing the P0456 Code

  • Double check for any technical service bulletins that may address a fix for the code
  • Be sure to check that the purge control valve is not defective.  Doing a thorough diagnostics of the system to later find the wiring is broken or cut can be easily avoided.
  • Verify that the leak is the problem before starting to replace random parts that may or may not be the problem

How serious is the P0456 code?

  • The code means the fuel vapor system has a leak.  This may be hard to locate on some vehicles and could cause the code to keep coming back until the leak is fixed.
  • Code P0456 causes the Maintenance Indicator/Check Engine Light to go on which can cause a failed emission test depending on your State’s regulations.
  • The PCM monitor will not pass emissions if the leak is not fixed.  Regardless of the status of your Maintenance Indicator/Check Engine Light.  Even if you were to shut it off, the codes will still be present in the PCM Module.

What repairs can fix the P0456 code?

  • Unclogging or replacing the leaking or clogged purge vent valve
  • Replacing leaking purge valve
  • Replacing leaking gas cap
  • Replacing leaking hoses or connectors within the system


While not the most common code, vehicles that come in with the Check Engine Light on with the P0456 code typically need a replacement fuel cap or the purge control valve or the vent valve will not hold in the vapors completely resulting in leaks detected.

Make sure you’re prepared for future issues by checking out our OBD2 Scanner Buyer’s Guide and purchasing the right one for your application.  They are super inexpensive and great to have around the garage for issues that may pop up unexpectedly.

Making sure you have the appropriate tools can be extremely helpful when these issues arise.  Our Torque Wrench Buyer’s Guide will tell you why they are important, how to use them, and which ones are best for your situation.

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