OBD-II Trouble Codes

P0456 Code: Evaporative Emission System Small Leak Detected

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What Does the P0456 Code Mean?

Diagnostic trouble code (DTC) P0456 stands for “Evaporative Emission System (EVAP) Small Leak Detected.” Your car’s computer may set this code if it determines that there’s a minor leak somewhere in the evaporative emissions control (EVAP) system.

The evaporative emission control system (EVAP) is a collection of components that work together to prevent fuel vapors from escaping into the atmosphere. This system must be free of leaks to comply with emissions regulations.

To check for leaks, your car’s primary computer, which is often referred to as the powertrain control module (PCM), will perform system self-tests when certain criteria are met.

During a typical “small leak” test, the PCM first opens the purge valve to create a vacuum in the system. The device then seals the EVAP system by closing both the purge valve and the vent valve.

a car engine
Your PCM may log the code P0456 if it determines that there’s a minor leak somewhere in the evaporative emissions control (EVAP) system.

Finally, to check for leaks, the PCM monitors vacuum decay via a fuel tank pressure (FTP) sensor. If a small leak is detected, P0456 or another small leak code may be set.

Typically, the PCM will only set the code if it sees the system fail the self-test twice.

The above description is how most systems operate. Keep in mind, however, that some vehicles use a slightly different method for identifying leaks. For example, some applications may use a leak detection pump and switch.

What are the Possible Causes of the P0456 Code?

There are several issues that could cause a P0456 code:

increased vehicle emissions
Increased emissions may be observed if your vehicle is running with a P0456 code.

What are the Common Symptoms of the P0456 Code?

Usually, a vehicle will continue to run even with a P0456 code because EVAP system leaks are often barely noticeable. The only symptoms you may observe that could be associated with this trouble code are the following:

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.

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. As such, diagnosis can be difficult. For an idea of how to troubleshoot the code, check out the videos below:

How to Fix the P0456 Code

There are multiple reasons why code P0456 might be stored. Therefore, there isn’t a “magic bullet” fix for the issue. You’ll need to diagnose the code accurately, as outlined above, then perform any necessary repairs.

The code could be triggered by anything from worn-out spark plugs to an internal engine concern, so you must do your homework.

Also, keep in mind that all vehicles are different. When troubleshooting and repairing diagnostic trouble codes, you should consult the factory repair information for your application.

Repair manuals, such as those from Chilton, are useful, but an ALLDATA subscription might be better. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information.

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