P0456 Code: Evaporative Emission System Small Leak Detected

Wondering why the check engine light is on and what is has to do with code P0456?

Your vehicle has a complex evaporative emissions system to prevent fuel vapors from leaking into your environment. An error code P0456 deals with this system and means there is a small leak detected. Learn more about this essential system and find out how do I fix trouble code P0456.

What does The P0456 Code Mean?

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.

The evaporative emission control (EVAP) system prevents fuel vapors from escaping into the atmosphere. The fuel vapors from the fuel tank are absorbed and stored by charcoal pellets in the charcoal canister.

The vent control valve is controlled by the engine control module (ECM) and allows air to flow into the charcoal canister to purge the gas vapors into the engine air intake to be burned. The flow of the gas vapors from the charcoal canister to the engine air intake is controlled by a purge volume control valve.

The vent control valve is usually open when the engine is at normal operating temperature, and the purge volume control valve is commanded when the ECM is ready to burn the built-up fuel vapors. However, when the vehicle is turned off the ECM performs a leak test to ensure the evaporative emission control system is working properly.

During the leak test, the ECM closes the vent control valve and purge valve to seal the evaporative system. If the EVAP system does not maintain the pressure, the ECM recognizes an evaporative emission control leak. In the case of P0456, it is a small leak, less than .020” in diameter.

P0456 Code

What Causes the P0456 Code?

Usually, this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could conceivably cause this code as well or if the cap wasn’t properly tightened. Any of the following could also be the cause:

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

What Are the Symptoms Of P0456?

It’s unlikely that you’ll notice any changes in the normal operation of your vehicle. The first sign of a trouble code P0456 will typically be your Check Engine light. Over time, you may notice a faint smell of gas or a slight decrease in fuel economy.

So, what does the code P0456 mean? These minor symptoms may make it seem like an issue that doesn’t need immediate attention. However, increased emissions can be harmful for the environment, particularly in closed areas. Check the common causes and look for a solution to promptly restore your evaporative emissions system.

How to Diagnose the P0456 Code?

To diagnose a P0456 code, you need to first make sure that the gas cap is securely fastened. A loose or faulty gas cap can easily trigger the trouble code. If tightening the gas cap doesn’t work, you may want to try purchasing and installing a new cap.

Keep in mind: once you’ve tightened or replaced the gas cap, you’ll have to clear the code with a code reader or scan tool afterward. The code won’t immediately go away on its own.

To be honest, you might have to hire a professional to find a very small leak. Even with the help of a smoke machine and other equipment, small leaks can be extremely difficult to locate. You can use a bright flashlight and do a visual inspection for split hoses or cracked plastic parts. The canister itself can leak as well.

Professionals will use very expensive scan tools to run an Evaporative Monitor procedure to determine whether a leak is present, both before and after repairs. But again, finding a small leak can be extremely difficult.

If a fuel pump has been replaced (gas tank removal), a small leak may result because of the fuel pump seal being out of place or because of some damaged or disconnected components on the tank.

If the gas cap doesn’t solve the problem, you’ll need to dig further. There are numerous potential causes for OBD-II code P0456.

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 Code P0456?

Very Low – It’s likely that you won’t notice any performance issues while driving your car with the P0456 code. For this reason, it may not be a priority to fix it.

With the emissions system not working as it should, you are allowing more pollutants to enter the atmosphere than needed. Your car may also fail an emissions test during this time.

Even worse, while the Check Engine Light is on, you won’t know if something else fails that needs your attention. For that reason alone, it’s best to fix the problem as soon as you can.

What Repairs Can Fix the P0456 Code?

After identifying its potential causes, it is only right to look into ways to clear the P0456 code. After all, we would not want to allow fuel vapors (a.k.a. hydrocarbons) to escape into the environment as pollutants. The right fix depends on what you find during diagnostics. Here are a few possible P0456 fixes:

  • Tightening a loose gas cap (or making sure you are using the right one)
  • Getting a new fuel tank gas cap or O-ring
  • Ridding the fuel filler cap and an inlet of blockage
  • Replacing the leaking/plugged purge vent valve.
  • Changing the purge control valve or EVAP hose
  • Swapping out damaged vacuum feed lines
  • Repairing damaged wiring/connectors
  • Replace the charcoal canister.
  • Replace the canister vent control valve.
  • Replace Fuel tank.

How Much Does It Cost to Fix Code P0456?

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.

For error code P0456, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.

  • Gas Cap – $20-$60
  • Evap Purge Volume Control Valve – $150-$200
  • Charcoal Canister Vent Control Valve – $150-$200
  • Replacement Evap Line – $50-$100
  • Charcoal Canister – $200-$600
  • Replace Fuel tank – $450 to $3,000.

Not all manufacturers use the P0456 code, so it isn’t as common as you may think. Yet, even when it does come on, it’s not normally indicative of a major problem. In most cases, you can simply tighten up the gas cap or replace it.

Even if there’s a part that needs to be replaced, the fix isn’t typically expensive, with many fixes costing $200 or less, especially if you can do the job yourself.

Other diagnostic codes related to P0456.

There are several other codes relative to this one.

  • P0440: Evaporative Emission Control System Malfunction
  • P0441: Evaporative Emission Control System Incorrect Purge Flow
  • P0442: EVAP System Leak Detected (Small Leak)
  • P0445: Evaporative Emission Control System – Purge Control Valve Circuit Shorted
  • P0455: Code P0455 indicates the PCM has detected a large EVAP system leak.
  • P0457: Evaporative Emission Control System Leak Detected