Subaru Outback P0456: EVAP System – Small Leak

This is one of the most commonly encountered trouble codes for the Subaru Outback The Code P0456. The trouble code refers to a number you receive when your Outback is plugged into an a OBDII scanner. The code P0456 indicates that the evaporative emissions control system has a tiny leak. It is sometimes found along with other codes such as P0440, P0441, or very frequently P0440.

The P0456 problem is not usually a threat to your Outback's driveability. Certainly anytime the service engine soon light is on, it’s good to deal with it as soon as possible.

While the trouble code may state that there is a “small leak” in the EVAP system of your Subaru Outback, it is actually referring to the amount of pressure lost, and not the physical size of the leak. This can happen in very small amounts.

Subaru Outback Definition P0456

The universal OBDII code P0456 can be used to diagnose any problem. The code can be used regardless of the make and model of your vehicle. Technically, the code stands for:

System Leakage in the Smallest Detail – Evaporative Emission System

The EVAP captures any fuel vapor in the tank. They are then sent to the engines intake for ignition. When there is a small leak in the Subaru Outback’s EVAP system, it will throw the P0456 OBDII Code. If there is a large leak, it’ll throw P0455.

Subaru Outback OBDII Codes Symptoms

A P0456 Code will not usually be associated with other noticeable symptoms. The smell of gas The service engine soon light.

Particular attention should be paid to the fuel tank or fuel filler tube smell.

Fuel vapors are dealt with directly by the EVAP. If these vapors are leaking from the system, you’ll often smell them faintly while operating the vehicle. But, it won’t affect the way the engine itself runs. The EVAP technology deals only with the fuel vapor. It does not impact the performance of your Outback engine.

Outback P0456 Trouble code Causes

Your Subaru Outback can trigger the P0456 code. If your Outback has warned you at all in the last few months that the fuel cap was off when it wasn’t, then replacing it would be a great first step.

These are some of the most frequent problems that can throw off the code. They're listed in alphabetical order, from the most likely to the least.

• Hose of the Evap System– The hose that carries the fuel vapor from the fuel tank to the intake manifold can begin to leak. The P0456 error code will be generated. It should be checked for tears or holes. This is the leading cause of code.
• Vapor Canister Purge Valve– One of the most common causes of the P0456 code is the vapor canister purge valve. It’s really easy to replace. There are some clips you will need to look for and then remove.
• Fuel Tank Sending Unit– It is possible for the gasket that attaches the fuel sending unit to the gas tank to go bad. This could cause a drop in tank pressure which can throw off the code.
• Fuel Cap– A bad fuel cap can cause the code to be thrown for sure. Often, you’ll get a message informing you that the fuel cap is off even when it is on. You may not get the message but a P0456. This will save you time and money.
• Fuel Filler Neck– There is often a gasket where the fuel filler neck connects with the gas tank. The gasket may dry out especially if the vehicle is in dry conditions. When it dries out, the fuel tank can’t hold pressure anymore.

Subaru Outback Diagnosis - P0456

The mechanic will have a lot of different tools at his disposal in order to determine the cause of your Subaru Outback P0456. These are some of the common diagnostics that can be done for the code

• The mechanic will usually check for additional codes. It is easier to diagnose problems if there are more codes. That’s because when they appear together in certain combinations, there will often only be only a few conditions that will throw any combination of codes at one time.
• The mechanic will normally determine what trouble codes are associated with P0456. Check out the EVAP System. These include the line and purge valve.
• To ensure that the cap can withstand pressure, the mechanic will check it. If you are getting a warning that your gas cap is off, even when it’s on, replacing it will more than likely clear this code.
• Monitoring and checking the fuel tank pressure is a must.
• Following the inspections and repairs, the mechanic will conduct two more tests.
• A smoke test, and they’ll use a scan tool to confirm that the EVAP solenoids and valves are operating properly.

Here’s a pretty good video on diagnosing these leaks from Scotty Kilmer, if you are interested:

Commonly Used P0456 Fixes

These are some of the most popular Outback P0456 solutions:

• Replacing the gas cap
• Replacing EVAP lines
• Replace charcoal canister
• Replacing the fuel tank

You should start with the gas caps and move on to the fuel tanks. This is because the gas caps are the most cost-effective and easiest to replace.

Here’s a great video on How to check your gas cap.

We wish you all the best in finding out why your Subaru Outback is throwing the code P0456. This should help. Please feel free to add anything below.

Do you consider P0456 to be a serious concern?

While P0456 is not going to cause the Outback’s engine to stop running, it should not be treated lightly. There could be fuel contamination. Check your fuel level to make sure it is not leaked. It is best to have it checked and/or dealt with immediately.

Please leave comments below if you have any suggestions. Thanks!