What Are The Symptoms Of A Bad EVAP Canister? - Vehicle Freak

• Luka Kusic

Updated on December 1, 2023

The Evaporative Emission Control System, also known as EVAP, charcoal, or vapor canister controls the gas fumes and prevents vapor leaks from the fuel system. This system has a significant effect on the reduction of emissions, as, without it, the gasoline would be able to evaporate even when the engine isn’t running. But what happens when the EVAP canister goes bad?

The prominent symptoms include: check the engine light turning on, hissing noise when opening the fuel tank, smell of fuel inside the cabin, issues with filling up the tank, and excessive smoke coming from the exhaust pipe.

How Does The EVAP System Work?

The EVAP system is not an auxiliary addition to the fuel system – it serves an instrumental role in keeping the engine supplied with fuel while preventing the vapors from escaping from the system.

Vapors are always present inside the fuel tank due to the nature of gasoline. To allow them to move on from the tank, a vent line diverts them into the EVAP canister, where the vapors are absorbed by active charcoal.

Once enough vapors have been stored, the purge flow sensor opens to allow the vapors to enter the throttle body and be used as fuel. The vent solenoid will now open to let air enter the EVAP canister and equalize the pressure.

Symptoms Of Failing EVAP Canisters

1. Hissing Sound

When you open up the fuel tank to refuel, you may have heard a subtle hissing sound. This typically happens when you’ve driven for extended periods of time, as the EVAP canister couldn’t equalize the pressure in time.

However, if the sound is very loud, and you even feel a gust of air passing through, the EVAP system is not purging enough vapors.

2. Smell of Gasoline

Noticing the smell of gasoline while near the vehicle is never a good sign. The highly flammable liquid quickly vaporizes and can ignite almost spontaneously, so you’ll have to check your entire fuel system to find the cause.

If not caused by physical damage to one of the components, the gasoline smell can be a result of a failing EVAP canister or fuel pump.

3. Check Engine Light

It’s common for drivers to ignore the check engine light, especially if they’re driving an older vehicle. While it’s true some warnings can be ignored, the check engine light will not give you a specific warning when a new problem emerges.

I would recommend that you either buy a or take your car for a diagnosis every few months just to check on the state of the vehicle. My current car throws a few pointless errors that cannot be permanently cleared, so by running the diagnosis more frequently, I can catch the more serious issues before they cause damage.

4. Smoke Coming From The Exhaust

The days of smoking exhaust pipes are long behind us, with only old 2-stroke and carburetor engines still puffing white clouds from the back. However, when a modern direct-injection engine starts producing visible white smoke, there’s likely a problem with the air-fuel mixture.

This is not commonly caused by the EVAP system, but it’s worth checking the state of the canister to eliminate it from the list.

5. Problems With Refueling

The gas station nozzle pours a large quantity of fuel quickly to make the refueling process faster. When you’re using a funnel to pour liquid into a bottle, you always raise the funnel slightly to let the air trapped inside the bottle escape and make the process faster.

Because the nozzle creates a decent seal on the fuel tank, the EVAP canister has to draw all the gas out of the tank to allow it to fill up with gasoline. If it’s clogged, the vapors will not be able to escape, and the safety feature inside the nozzle will stop your refueling prematurely. If you’re experiencing this problem, don’t try to force more fuel into the gas tank, and instead, use what you’ve got to get yourself to a mechanic.

How to Replace EVAP Canister

Replacing the EVAP canister at home isn’t a difficult task, but there’s one thing to keep in mind. As you’re dealing with gasoline vapors, one spark, one metal-on-metal contact can be enough to cause an explosion. The likelihood of this happening is low, but I need to make sure you approach the job with precision and care.

Tools you’ll need:

The average cost of labor to replace the EVAP canister is $100, so it makes a lot of sense to invest in your own tools. Nearly everything on the list is a must-have tool that will come in handy whenever you’re repairing something on your vehicle, or even home.

Steps to replace the EVAP Canister:

1. Lift the back of the vehicle on jack stands to gain access to the EVAP canister.
2. Locate the EVAP canister – in terms of shape, it’s similar to the exhaust muffler.
3. Unscrew the bolts holding the canister in place.
4. Wires need to be disconnected before the canister can be removed.
5. Take the canister out of the protective casing and compare it to the one you’ve bought.
6. If your replacement came without an evaporator, use the one attached to the old canister.
7. Put the new canister back into the protective casing.
8. Underneath the vehicle, attach the wires, then screw the casing back in place.

Take a look at this excellent tutorial on how to remove and install an EVAP canister.

FAQs

How much does it cost to replace a vapor canister?

On average, the cost of labor is $100, while the total cost depends on the cost of the EVAP canister. Most conventional cars use a $100 vapor canister, for a total cost of $200-250.

Can you drive with a bad EVAP canister?

A bad EVAP canister will not prevent you from driving your vehicle. However, but the smell of gasoline and not being able to pass emission standards are enough of a reason to get the canister replaced.

Can you clean an EVAP canister?

Technically, it’s possible to clean active charcoal by using compressed air, but never with liquid! The effectiveness of cleaning the EVAP canister is uncertain, so if you’re taking the time to remove it, you should also replace it.

Do you need a vapor canister?

The vapor canister and the entire EVAP system are necessary to prevent excess emissions, so you should never attempt to remove or bypass them. Not only is it illegal to remove the EVAP system, but it also causes the vehicle to fail the emission tests.

What are the symptoms of a bad purge valve?

Problems with the purge valve will not be the same as those relating to the EVAP canister. You may experience difficulty starting the engine and a rough idle along with poor performance and fuel economy. The check engine light should turn on to notify you that there’s a problem with the purge valve.

Summary

Now that you know what the symptoms of a bad EVAP canister are, you can gather the tools and replace the canister yourself. That way you’ll not only save money on a mechanic but also learn a new skill and keep all the tools for the next DIY job!

Find out more information with these related posts:

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