What is an evaporative emission control canister?
An evaporative emission control canister—also known as a vapor canister, charcoal canister, or EVAP canister—is an emissions control device designed to capture the fuel vapors that build inside your fuel tank.
The canister is part of the evaporative emission control (EVAP) system. It connects to your fuel tank and collects excess gas vapors. The canister’s charcoal filter converts the vapors into hydrocarbons and carbon dioxide.
The hydrocarbons flow through the purge valve into the intake manifold, where they combine with the air/fuel mixture before burning up during the combustion process. The carbon dioxide exits the EVAP canister through the vent valve and flows into the outside environment.
The EVAP system not only reduces the amount of harmful pollutants your car releases, but also improves fuel economy and engine efficiency.
When should I replace the EVAP canister on my car?
Because there is no set replacement schedule for the EVAP canister, you’ll only need to replace yours when it fails. These are the most common symptoms of a bad charcoal canister:
Check engine light (CEL): When your car’s engine control module (ECM) detects a problem with the EVAP system, it will most likely illuminate the CEL. Remember, though, that this light can appear for many reasons. To diagnose the trouble code, you’ll need to use an onboard diagnostics (OBD) scan tool.
Fuel odor: A faulty EVAP canister can allow fuel vapors to leak into the air. If you smell a strong fuel odor near or in your vehicle, it could be a sign that you need a new EVAP canister.
Performance issues: A bad EVAP canister can negatively affect your engine’s air/fuel mixture. This can lead to a variety of performance issues, including reduced fuel economy, a rough idle, difficulty starting, and engine surging.
Failed emissions test: If your EVAP canister is bad, you’ll most likely fail an emissions test. Depending on where you live, this can render your car illegal to drive.
Collapsed fuel tank: When the EVAP system has a severe failure, it can cause the gas tank to collapse or leak. You’ll likely notice a whooshing sound when you remove your gas cap if there’s an issue with the vapor venting process.
Keep in mind: These issues can be indicative of other issues with the air intake or fuel systems, like a faulty fuel pump or clogged air filter. It’s always best to visit a certified mechanic to get an accurate diagnosis.
How often should I replace my evaporative emission control canister?
There is no set replacement interval for the EVAP canister. In fact, it’s common for the canister to last for the life of the vehicle. That said, they can and do fail over time.
You should replace your EVAP canister if you see signs of its failure, including a check engine light, a strong fuel odor, or a collapsed gas tank.
Can I replace my EVAP canister myself?
An EVAP canister replacement is a mid-level repair job. It can make a great DIY project for moderately-experienced home mechanics, but novices may struggle.
If you have access to the proper tools and are confident in your abilities, you shouldn’t have any trouble completing the project at home. But if you’re uncomfortable working with the evaporative emission control system or don’t have the correct tools, you should contact a professional mechanic.