Skip the auto shop - Our mechanics make house calls

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

check engine light

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Shutterstock.com Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....
P2422 OBD-II Trouble Code: Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed
Diagnostic Trouble Code (DTC): P2422 P2422 code definition Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed Related Trouble Codes: P2441: EVAP Vent Valve Stuck Open EVAP trouble...


Related questions

Q: Computer reads an issue with the oxygen sensor on a Subaru Forester 1999 2.0 Turbo. What is the problem?

Your 1999 Subaru Forester has pre and post catalytic converter oxygen sensors. The pre-converter sensor optimizes fuel trim while the post converter sensor monitors the efficiency of the catalytic converter. A failing pre-converter sensor will degrade vehicle MPG performance. Although...

Q: Car hesitates to start check engine light and VSA light comes on car has no power only gets up to 45 and crawls going uphill 2008 Honda Accord

Hi there - the Vehicle Stability Assist system utilizes wheel speed sensors, and your cars anti-skid braking system to assist with car control in extreme cornering or braking circumstances. It also reduces engine power to moderate vehicle behavior. Check the...

Q: I'm getting a check engine light with codes p0455 and p0456. I tried a new gas cap from the dealer but the light comes back in a few days.

Hi there - the 2 codes you mention are indicative of a leak in the evaporative emissions system. As you have been advised, this is sometimes caused by a loose gas cap, or one that no longer seals properly. It...