Understanding Your Car’s EVAP Canister

Gasoline is called gas for a reason; when exposed to air, it quickly evaporates out of its liquid form. This occurs even when the gas is in your tank, and it is one of the reasons your car is required to pass emissions tests. Luckily, almost all cars are equipped with a charcoal evaporation (EVAP) canister, which catches and filters the vapor. Although this part of your car seems fairly inconsequential, it plays an important part in ensuring the safety and environmental friendliness of your vehicle.


The EVAP canister exists to control the emissions from your gas tank. Essentially, your gas tank is constantly emitting vapors. The EVAP canister contains a charcoal lining, which is used to trap these emissions. When you turn your engine on, another part of your emission control system will filter these emissions back into your engine, where they can be used. This improves your fuel efficiency and helps you pass emissions tests. Otherwise, it doesn’t actually affect the function of your car.

Checking for Damage

Whenever you do a routine maintenance on your car, you should check your EVAP canister and the surrounding system for damage. The first step is to find the canister. On many cars, the canister is located on the driver’s side of the car toward the rear; it should be a black container, roughly the size of a can of beans. If you aren’t sure where it is, reference the diagram in your owner’s manual to find it.
Once you have located the canister, do a cursory check to see if you notice any cracks or damage on the canister or the surrounding hoses. Damage is rare, but if you have a crack, it can cause you to fail emissions tests. If you don’t notice anything, and you are getting good emissions scores, then no further action is needed.

OBD Code P0455

The on-board diagnostics code system is a way to identify problems with your car. A common code is p0455, which indicates a fuel vapor leak. According to OBD-Codes, there are two main causes for this: either a loose gas cap or a broken EVAP canister.
If the problem is your EVAP canister, you likely need to look into a replacement fairly soon. The code won’t affect the function of your vehicle, but it will cause you to fail emissions, so you should replace it sometime before the next test.

Replacing the Canister

The process for replacing the canister is fairly simple. However, if you aren’t good with cars, you should consider having a mechanic do it for you. Because you are working with the gas tank, you don’t want to risk any damage to your car.
The canister itself will be connected in two sections: a hose on one side, and a bracket attached to the canister on the other. You can pry the hose off with a pair of pliers or a flathead screwdriver, but you will need a regular screwdriver to remove the bracket. Then, you simply re-attach the new canister using the same method, and you’re done.

You don’t need to worry about your EVAP canister every day, but you should include it in your routine car maintenance checklist. Give it a look over when you change your oil, check your tire pressure, or clean your windows. You probably won’t notice any cracks, but they do appear once in a while. By keeping an eye on it, you can save yourself a little gas money and ensure that you will pass your next emissions test with flying colors.