Estimates Trouble Codes P0456

P0456: EVAP System Leak

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What is P0456?

P0456 is a generic On-Board Diagnostics System (OBD II) code indicating that your evaporative emission control (EVAP) system has sprung a small leak.

Essentially, the EVAP system stores fuel vapor in charcoal pellets in the charcoal canister or EVAP canister. These fuel tank vapors are then rerouted for combustion rather than dispelled into the atmosphere. 

Aside from the environmental benefits, this also improves fuel efficiency and keeps your car from smelling like gasoline with the help of the cabin air filter.

The Powertrain Control Module or Engine Control Module handles most of your car’s systems based on the information it receives from various sensors. One of these is the pressure sensor in your vehicle’s evaporative emission system. When the fuel tank pressure sensor detects a leak, it triggers a P0456 code. Your vehicle’s Powertrain Control Module (PCM) or Engine Control Module (ECM) performs various tests on your EVAP system. The test has to fail twice before triggering a P0456 code.  

 Most vehicles built after 1996 come equipped with the OBD-II system, and it’s there to detect emission problems before they become a significant issue.



Common symptoms

The most obvious sign of a leak in your EVAP purge line will be the Check Engine Light illuminated on your dashboard. However, because the EVAP is a closed system, it can be difficult to notice other symptoms. 

With that said, if the problem goes unchecked, you should start noticing some telltale signs. If you note a decrease in your fuel efficiency, an increase in emissions, or a fuel smell in your car, it might be worth checking the evaporative emissions system. 


Can I still drive?

The good news is that a P0456 code isn’t serious and will likely have a minor effect on your car’s performance. 

Although a P0456 code is unlikely to cause catastrophic failure, it’s still essential to have the issue repaired as soon as possible. Your vehicle will fail an emissions test if the leak isn’t patched.

P0456 causes

Your vehicle runs routine tests to ensure everything is working as it should. The car tests the EVAP system using the engine intake manifold vacuum. If the pressure remains stable, the ECM checks for leaks between the fuel tank and the EVAP canister purge solenoid valve. 

The ECM commands the purge control valve to close the system and activate the evaporative vacuum pump to create a slight vacuum. 

If there are any leaks, it stores the code until it can do a second test. If it detects the leak again, it’ll trigger a P0456 code. 

However, the leak itself has many potential causes, including:

  • A damaged or loose gas cap
  • A disconnected EVAP hose
  • Faulty purge volume control 
  • Faulty canister vent
  • EVAP canister leak
  • Leaking fuel tank
  • Purge solenoid valve is stuck or won’t close properly
  • Loose fuel tank hoses
  • Fuel filler cap fails to close 
  • Incorrect fuel filler cap applied


Diagnostics play a crucial role in fixing a P0456 trouble code. Since the leaks are usually tiny, identifying the issue can be challenging. Mechanics can often spend a day finding and repairing the leak. 

Typically, a technician will follow these steps: 

  • Step 1: The mechanic begins by connecting an OBD-II scanner and noting down the error code and freeze frame data. 
  • Step 2: A thorough inspection of the vapor purge valve should follow, checking the hoses, connectors, and the valve itself. 
  • Step 3: The mechanic must also check the purge control valve to ensure it’s not blocked by dirt or debris.
  • Step 4: The fuel tank and the charcoal canister will also need to be inspected for leaks. 
  • Step 5: The mechanic should also check the purge valve and charcoal canister vent valve are working correctly by testing them with a multimeter. 
  • Step 6: If the mechanic still hasn’t found the leak, they will likely do a smoke test. Using a smoke machine will make locating the leak in the EVAP system much more manageable.

Assuming the purge control valve is the issue without properly checking the part or doing a thorough diagnostics of the complete system is a common mistake. This will lead to wasted time and money. 

Additionally, it’s easy to assume a loose fuel cap is the only problem without performing additional checks to determine if there are leaks elsewhere in the EVAP system. 

Many car manufacturers have technical service bulletins regarding EVAP codes. By checking these, you may find some help in diagnosing or preventing a misdiagnosis.

Possible repairs for P0456 & Costs

Once the mechanic has identified the leak, it’s a matter of replacing the damaged part. It’s easy to switch out the gas cap or purge valve if they’re the culprit. If the purge vent valve is clogged, cleaning it out and replacing it shouldn’t be too much hassle either. 

A P0456 code probably won’t damage any other components, so there shouldn’t be any resulting damage to repair. 

Most evaporative emission system leaks are too small to see, so diagnosing a P0456 code can be tedious. 

If you’d rather save yourself the trouble, contact AutoNation Mobile Service. We’re a convenient mobile auto-repair and maintenance solution capable of fixing your P0456 error code wherever you are. 

Here are a few reasons why customers love us:

  • Error code diagnosis and repairs can be made right from your driveway, office, or wherever you are
  • All repairs and maintenance are performed using only high-quality tools and parts
  • Competitive and upfront pricing
  • ASE-certified mechanics 
  • Easy and convenient online booking 
  • 12-month | 12,000-mile warranty on all repairs

A minor leak could set you back anything between $200 and $300. A $100 diagnostic fee is standard in many shops, with an additional $100 if the leak is difficult to find or if the components are hard to reach. 

In many cases, the repair is a new hose, a rubber gasket, or a new fuel cap, which are inexpensive. However, it’ll likely be more expensive if the leak stems from the filler neck or the gas tank. In this case, you could expect to pay between $500 and $600.

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