What you NEED to know about P0455 and how to FIX it! (EVAP)
The check engine light is a bummer to all vehicle owners. As soon as that light illuminates, it can be game over for some.
Finding out that your vehicle has diagnostic trouble code P0455 can result in a costly repair.
In this article, we will look at what it takes to fix that fault code and what the mechanic sees with his or her scan tool.
The evaporative emissions system can be a common problem among many vehicles. An EVAP code can illuminate the check engine light for a small leak, a large leak, or a component failure.
A common code that pops up in vehicles is the code P0455.
From leaks in EVAP hoses to component failures, we will find out what can cause the P0455 trouble code.
What does P0455 code mean?
The P0455 fault code indicates a large leak in the EVAP system. (Evaporative Emissions System)
This could also be stated as a "gross leak".
This fault code may lead you down the wrong path if not diagnosed properly. In some cases, a P0455 code can be an EVAP vent valve that is stuck open. This will not allow correct vacuum in the EVAP system while the engine control module is performing a leak test.
During a leak test, the engine control module monitors the fuel tank pressure sensor for changes in pressure. If an EVAP vent valve is stuck open, then the EVAP system can not properly seal itself, thus not being able to hold a vacuum.
If your system does not have a large EVAP system leak, then it may be a component failure.
The above picture is an EVAP vent valve.
What would cause a large EVAP leak?
Large EVAP leaks can be caused by an actual leak in the EVAP system or a failed component.
Leaks can be found in the plastic or rubber hoses that are used in the EVAP system. Some leaks can be caused by physical damage from road debris.
Some other leaks can be from the fuel filler cap, gas tank, or charcoal canister (EVAP canister).
Possible causes of failed components that cause the code P0455 are:
Bad Vent Control Valve (Vent Valve)
Lack of purge flow - This can be caused by a bad purge valve.
Incorrect pressure data - The engine control module (ECM) monitors the fuel tank pressure sensor voltage for leaks. If the fuel tank pressure sensor is sending the incorrect voltage, the ECM can misinterpret the data as a leak.
How do I fix code P0455?
The best way to fix a P0455 is to have the right diagnostic process to get to the root cause of the problem.
This is what most mechanics do to test for EVAP codes.
Have a visual inspection of every component and hose to make sure they are in good condition.
Bi-directionally control each component with a scan tool to ensure proper function.
Do a manual EVAP test with your scan tool.
Perform a smoke test if a leak is suspected.
Is it safe to drive with code P0455?
It is important to properly diagnose the code P0455 and repair it soon. The vehicle may stop monitoring and testing other codes if P0455 is present.
A large fuel vapor leak may be present in the Evaporative Emission System (EVAP) which is not ideal for driving a vehicle.
Can a gas cap cause a large EVAP leak?
Yes, if a gas cap is severely damaged or has something that keeps it from sealing properly, then it can cause a P0455 code.
A bad gas cap has to be replaced with a new gas cap if the gasket on it is not sealing properly.
In some cases, a loose fuel cap will cause a small EVAP leak, but sometimes the tether that attaches the gas cap to the vehicle can obstruct the gas cap from closing fully. Check out the photo below for an example of a gas cap tether not allowing the gas cap to seal all the way.
How much does it cost to fix code p0455?
Fixing a P0455 can cost anywhere between $20 - $250 to replace an EVAP vent valve.
This price is depending on if you replace it yourself and the price of your specific vehicle's part.
When using an auto repair shop, the price will go up due to labor costs.
There are benefits to using an auto repair shop. For instance, warranties are usually issued by the auto repair shop if the part that was replaced was defective. The auto repair shop will usually take its time to properly diagnose the issue in order to repair the problem the first time. This can save you money in the long run.
If you decide to repair it yourself, there is an online resource I use on every vehicle, which is AlldataDIY.
AlldataDIY has all of the repair information for your vehicle. It also has wiring diagrams and technical service bulletins.
Repair your car the right way with AlldataDIY.
How do you find a large EVAP leak without a smoke machine?
A large or small EVAP leak can be very difficult to find without doing a smoke test. A smoke test will reveal the leak much faster than any other method.
Other proper equipment is needed to perform a smoke test, like an advanced scan tool. Having a sealed EVAP system is ideal for performing a smoke test. A scan tool is needed to fully seal the system. Rubber plugs may be able to do the trick too, if placed properly.
Other leak tests are possible, like using CO2 to fill the EVAP system and using a CO2 detector to find the leak.
Smoke machine
How serious is a large EVAP leak?
An EVAP large leak can be a serious issue in vehicles. In some cases, the EVAP leak can be located inside the vehicle. This allows fuel vapors to be inside the vehicle, which is not ideal.
Check out this case study of a Subaru with a DTC P0455. It was found that the leak detection pump was leaking and allowing fuel vapors to leak into the cabin of the vehicle.
Different monitors and tests performed by the ECM are put on hold when the P0455 code is active. There may be another issue with the car revealed once all of the monitors have run.
Without the other monitors and tests running, there may be an issue that affects fuel economy also.
For instance, check out this case study of a Ford Mustang that had an EVAP purge valve issue. The purge valve was not sealing properly and allowing fuel vapors into the engine at the incorrect time. This caused the Mustang to have a "rich" condition and a code P1450.
It's best to have the P0455 issue resolved so that the vehicle can run through all of the monitors and tests that it needs to operate efficiently.
If you have found a leak or a component that has failed on your vehicle and repaired it, the vehicle will have to go through a "drive cycle" to run all of the tests and monitors. In some instances, it can take a long test drive or several test drives for the EVAP monitors to run. This is why when you clear an EVAP leak code, it takes days for it to come back on.
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