Evap Canister Failure Symptoms and Causes

The evap canister performs an essential function inside a vehicle. If this part is not working correctly, a vehicle may fail an emissions test. There are a few signs that appear if your canister is failing. We will discuss symptoms, causes, and what to do if you find that your evap canister is not working.

Evap canisters are usually rectangular and mounted inside of the vehicle. It contains activated charcoal, which stores and absorbs gasoline vapors. The vapors are stored in the evap canister until a car is being driven. They are normally made of plastic.

What Does an EVAP Canister Do?

An evap canister is used to absorb gasoline vapors and store these vapors until the car engine is in use. Once the car is being driven, the PCM (powertrain control module) opens the purge valve, which is attached to the canister. An intake vacuum will then pull these vapors into the engine. The fuel tank vent line connects the canister to the fuel tank.

This canister helps the environment by limiting the vapors that are released into the air. A working canister also helps a vehicle to maintain good gas mileage and keeps drivers from experiencing the strong smell of gasoline fumes inside and around the car.

Where is the Evap Canister Located in the Car?

The canister is located in the same area as the fuel tank. The vent valve is underneath the vehicle by the fuel tank, close to the canister.

Evap System Diagram

The location of this part may differ in varying vehicle models, but seeing one can give you an idea of what any evap system will look like. Viewing a diagram will help in understanding how the evap system is connected.

How to Tell When an Evap Canister is Bad?

A few signs can alert a vehicle driver that the evap canister is bad. Below is a list of some of the most common symptoms of a defective canister. Each of these symptoms should be checked out by your mechanic because the part may need to be replaced.

1) The Check Engine Light Comes On

The Check Engine light is always a cause for concern. It could signal various issues, so it’s best to consult with an automotive technician to determine the exact cause.

2) Problems With Filling Your Gas Tank

If the gas meter of the car always seems to be low or if you have problems whenever you go to fill up the tank, that could be a sign that something needs to get cleared out or replaced.

3) You Smell Fuel Inside and Around Your Vehicle

Smelling gas while inside your car is never a good sign because it may mean a leak somewhere.

4) Hissing Noises When You Open the Cap to Your Fuel Tank

The fuel tank should not produce any noticeable sounds. There may be a problem if it makes a weird noise, such as a hiss.

What Causes Evap Canister Failure?

There are four likely causes for a failing evap canister.

1) Cracked Evap Canister

Erosion can cause cracks in an evap canister. These cracks prevent the canister from absorbing and storing fuel vapors. These fuel vapors will then go out into the environment, adding to existing pollution.

2) The Canister Gets Clogged

A canister can become clogged if the fuel vapors that typically get used up during combustion do not make it to the combustion chamber.

3) Topping Off Your Gas Tank

Repeatedly over-filling your gas tank can cause liquid to enter the canister, which is only designed to store vapor. This liquid can clog your evap canister, which causes a faulty canister.

4) Problems with Related Valves

Often evap canisters will stop functioning correctly due to issues with other related valves. The problem may not be the actual canister.

How to Fix a Bad Evap Canister?

If an evap canister is not functioning correctly, it will need to be replaced. The canister cannot be repaired while it’s still on the vehicle. The damaged part should be removed, and it is best to consult your vehicle’s manual before attempting. In some vehicle models, the canister is in the rear, and on other models, it may be found in the front of the vehicle.

The vehicle needs to be raised to get to the part. This requires jacks or jack stands or a hydraulic lift. You will also need to remove the vehicle’s battery’s power before proceeding. Before touching any parts, be safe and remove the negative and positive terminals from the vehicle’s battery.

How Long Should an Evap Canister Last?

As with any vehicle part, many things can cause damage and prevent your vehicle from performing at its best. The evap canister is no different. In many cases, the evap canister will last the vehicle’s lifetime, but it is important to notice any of the signs of a failing canister.

One of the evap canister functions is to reduce fumes that could cause headaches and other physical feelings of discomfort. The evap canister limits the smell of gas fumes inside and around your vehicle. So if you do detect that it is damaged, it is best to get the car checked out to see if the canister needs to be replaced.

Can You Bypass the Evap Canister?

A vehicle can undoubtedly run with a failing or damaged evap canister, but there are consequences to ignoring a failing part. Though a car may be driven without an evap canister or with one not functioning well, the vehicle will most likely fail an emissions test.

You may also experience issues with your vehicle, such as losing gas mileage and the strong smell of fumes inside and around the car, which could make you ill. There is also the environment to consider because an evap canister helps to eliminate fumes that pollute the air.

Technically, a vehicle will run with a damaged canister or even without one, but choosing to bypass this part is not recommended.

So Should It Be Replaced and How Often?

If signs of a failing evap canister are evident, then a mechanic should check out the vehicle. There are error codes that are triggered by a bad evap canister, and a trained mechanic will recognize those codes. If it is determined that the canister is failing, cracked, clogged, or damaged in any way, it will need to be replaced. It cannot be serviced or repaired on the vehicle.

The bottom line is that vehicles require care and maintenance. If any of the signs that have been described here seem familiar, it is advised to get the car checked out by a trained mechanic. If a faulty evap canister is the cause of any vehicle trouble, it is best to have it replaced.

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Author: Dave Johnston

Dave Junior is a hands-on automotive technician with experience in performing service, diagnostics, and repairs on domestic and imported vehicles. He enjoys writing and sharing his knowledge far and wide.

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