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EVAP Leaks: Why Do They Happen And How Do I Fix Them?

Feeling some persistent and lingering smells of gasoline in and around your car? You may experience an EVAP leak problem.

It is important to note that you should fix the problem immediately because it is not only dangerous to you but also makes you fail the state-mandated emissions test.

This article will enable you to understand the roles of the EVAP system in your car, how to identify the EVAP leak problem, and what you should do in this situation – Fixing it yourself or bringing your vehicle to a professional mechanic.


EVAP leak is an auto part fault in your vehicle’s evaporative emission control system

EVAP system prevents gasoline vapors from escaping into the atmosphere
Credit: aa1car.com

EVAP system

The vehicle’s evaporative emission control system (or EVAP for short) is a component designed to combat unchecked pollution. When operating regularly, the EVAP system works to contain extra gas fumes from your gas tank and prevent them from leaching out into the air and atmosphere. This, in turn, cuts down on the overall air pollution, a hazardous problem that has become particularly acute in urban environments over the past several decades.

The EVAP system is made up of several parts, all of which can face some trouble over the lifespan of your vehicle. These parts include the gas tank, gas cap, liquid-vapor separator, and EVAP canister.

EVAP leak

Simply put, an EVAP leak is an auto part fault in your vehicle’s EVAP system. Because of the nature of the EVAP system, this means that your gas cap is loose or gasoline fumes are leaking from your gas tank, even when it is not in operation. As such, an EVAP leak could potentially pose a threat to your well-being as well as the health and safety of those around you.


 If your Check Engine Light does come on, and you just filled up your gas tank, check the gas cap to see if it's loose
Check Engine Light
can indicate any number of vehicular problems, including problems with the EVAP system
Credit: commons.wikimedia.org

There are several methods for identifying an EVAP leak, including several systems built into your vehicle. One of these methods is by noticing that the “Check Engine” light has become illuminated while operating the vehicle. This light (also known as the “malfunction indicator light” or MIL for short) can indicate any number of vehicular problems, including problems with the EVAP system. If you take your vehicle to a mechanic to read out the specific fault code, they may determine that the problems of the EVAP system caused the light.

Another sure sign that something is amiss with the EVAP system is a persistent and lingering smell of gasoline in and around your vehicle. While this may be a residual smell after a tank fills up, it may also indicate that some gaseous fumes are escaping the main tank. This smell may be most apparent wherever the car spends most of its time inactive, such as a garage.

Loose Gas Cap is the most common cause of an EVAP leak.
Credit: commons.wikimedia.org

Also, if you notice an active leak from your gas tank (in the garage or elsewhere), this is likely a sign that the EVAP system is having some trouble. If this latter scenario is the case, do not operate your vehicle until a trained professional has an opportunity to evaluate it.


Though fixing an EVAP leak can take some time and knowledge, there are some simple fixes that you can try before seeking out a mechanic.

First and foremost, manually check to ensure that your gas cap is secured correctly and remains secured after driving the vehicle. In some cases, the O ring inside the cap may degrade, causing it to deteriorate and leave an opening in the vacuum-sealed EVAP system. This is the most common type of EVAP leak and the simplest to fix.

Using an OBD-II scanner (available at most auto parts stores), you can also check the EVAP status based on internal computer readouts. After following the instructions to perform a scan, your scanner will return an error code (if a fault is present). If the code ranges from P0440 to P0457, you may have an EVAP leak on your hands (see below for more information).

Beyond this, though, you will likely need to seek a mechanic in order to resolve your EVAP problem. Other potential problems could involve a faulty vacuum control solenoid as well as a faulty purge solenoid. In either case, You will need a person who has specialist knowledge and tools to access most of the EVAP system, located under the vehicle and near the gas tank.


An EVAP error code is a specialized output by your vehicle’s on-board diagnostics system (OBD-II) to indicate something is amiss with your EVAP system. Here are some common codes for EVAP problems.

  • P0411 EVAP System Control Incorrect Purge Flow
  • P0440 Evaporative Emission (EVAP) System
  • P0446 EVAP Vent Solenoid Valve Control System
  • P0455 Evaporative Emission (EVAP) System Large Leak Detected 
  • P0456/P0442 Evaporative Emission (EVAP) System Small Leak Detected

If the error code ranges from P0440 to P0457, then you likely need to seek out professional help to resolve the leak and the code.


You should not drive for long while when having a leak.

EVAP leaks do not immediately affect how your vehicle operates.
Credit: pixabay.com

In general, EVAP leaks do not immediately affect how your vehicle operates. However, that does not mean you should disregard it out of hand. In fact, because this leak involves a portion of the gas tank system, you should take it rather seriously.

Anytime leaking liquid gas or gas fumes are involved, you and those around you are at risk of inhalation or injury from the ignition. Though these are not likely, they are still a potential risk associated with operating with a persistent and unresolved – EVAP leak.

In any case, driving with EVAP leaks means that you are very likely polluting the air 24/7. While this is bad for the environment at large, it also means that you are likely to fail a state-mandated emissions test, should one be administered.


The short and long of EVAP system leaks is that you should take them seriously. With a potential leak in petroleum fumes, you may be harming not only yourself but also the people and environment around you.

While you may be able to quickly identify an EVAP leak based on the smell of gaseous fumes, you may need to seek out a mechanic to fully resolve it (beyond attempting several manual and scan-based tests). While it is regularly safe to drive with an EVAP leak, you should only attempt to do so for as long as it takes to bring the vehicle to a mechanic for repairs. Now that you know about EVAP leaks and how to resolve them, you can make informed decisions regarding your vehicle’s future maintenance.

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