What Is an EVAP Leak And How Do You Diagnose It?

Leaking fuel vapors is no laughing matter.

byChris Teague|
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Check engine lights are sometimes accompanied by noises, smells, and vibrations that can help diagnose the underlying issue. But sometimes, that annoying little light comes on with no other indication of what’s up. That’s sometimes the case with leaks in the EVAP system.

What is an EVAP leak, you might be asking? We’ll get to that. Right now, the important things to know up front is that the EVAP system is related to your vehicle’s emissions control systems and that it’s responsible for protecting the environment from the nasty stuff that the vehicle produces. That’s good!

If there’s a leak, your car won’t burst into flames, but it’s not a problem you should ignore. That’s not! In this post, The Drive’s screw-loose editors will tell you why that is, and will also get into what causes the leaks and how you can diagnose them yourself. Onward!

A mechanic can help diagnose the issue., Depositphotos

What Is The EVAP System? 

Your vehicle’s EVAP system (evaporative emissions control systems) are in place to prevent fuel tank vapors from escaping into the atmosphere. All cars and trucks are required to have an EVAP system to protect the environment from harmful fuel vapors and you from breathing them in.

How Can I Tell If There’s A Leak?

The main indicator that accompanies EVAP leaks is the check engine light. You may notice a faint fuel odor, but the problem manifests itself differently in different vehicles. A common issue is a loose gas cap, which can cause the check engine light to come on in newer vehicles as the ECU senses a problem with the EVAP system. If you see the check engine light and haven’t filled up with fuel recently, it’s a good idea to use a code reader or take your vehicle to a shop for diagnosis.

Is It Safe To Drive With An EVAP Leak?

It’s technically safe to drive with a leak, but it’s absolutely not recommended. You probably won’t burst into a ball of flames while driving, but you will be exposing other people and the planet to your vehicle’s fumes. That’s not a good look.

How Much Will This Cost To Fix?

Depending on where the leak is in the system and whether or not there is another damage, you can expect to pay up to $600 or so to fix a leak in your vehicle’s EVAP system. If you have an OBD2 code reader at home, you can diagnose the problem yourself, but it’s best to leave the fixing to the professionals.

EVAP System Terms You Should Know

Get educated!

EVAP System

As part of a vehicle’s emissions control system, the EVAP (evaporative emissions control) system traps fuel vapors from evaporated fuel. The system then sends the fuel back to the tank for use.


Emissions refer to the gases, vapors, and other pollutants that are emitted from the daily use of vehicles.

Check Engine Light

The check engine light is a warning indicator that is illuminated when the vehicle’s electronic control unit (ECU) detects a problem with a system, sensor, or component. It’s frequently seen in combination with noises, vibrations, and other symptoms, but with an EVAP leak, it might be the only indicator that something is wrong.


OBD2 or on-board diagnostics systems are a vehicle’s self-diagnostic and reporting mechanisms. The vehicle’s computer generates codes that correspond to various issues, which can be read and interpreted with a scanning tool at home or at a repair shop.

Tailpipes are just one source of pollution., Depositphotos

Get Mobile Evap System Service and Repair with YourMechanic

While The Drive’s how-to guides are detailed and easy to follow, no vehicle is created the same, and not all auto maintenance or repair tasks are easy to accomplish on your own. That’s why we’ve partnered with YourMechanic and their network of mobile automotive technicians to offer our readers $10 off a $70 or more service call when you use promo code THEDRIVE.

FAQs About EVAP Leak  

You’ve got questions, The Drive has answers!

Q: What Codes Should I Look For On My OBD2 Scanner?

A: Some common codes include:

  • P0442 - Small leak detected
  • P0445 - System leak detected
  • P0440 - EVAP System
  • P0446 EVAP Vent solenoid valve control system
  • P0411 - EVAP system control incorrect purge flow

You may see other codes present, as the EVAP system has codes that run from 0440 to 0457.

Q: How Do I Reset The Check Engine Light And Code?

A: This process will differ based on the type of vehicle you own. Some models require the driver to turn the vehicle on and off a few times while placing the system into accessory (ACC) mode, while others require some combination of holding the trip reset button while pressing other controls. You can find the process for your specific vehicle through a quick Google search, or by using a maintenance or repair manual for your model.

Q: Is There A Way To Prevent EVAP Leaks?


Regular inspection and maintenance of your vehicle’s fuel system is the best way to prevent EVAP leaks, but sometimes things just happen. The most common causes for EVAP leaks include bad seals and O-rings, a failing purge valve, a damaged hose or vent, or a defective leak detection pump. As you might have guessed, there’s no real way to prevent one of those components from failing unless you’d like to regularly replace components of your fuel system.

Let’s Talk, Comment Below To Talk With The Drive’s Editors!

We’re here to be expert guides in everything How-To related. Use us, compliment us, yell at us. Comment below and let’s talk! You can also shout at us on Twitter or Instagram, here are our profiles.

Jonathon Klein: Twitter (@jonathon.klein), Instagram (@jonathon_klein)

Tony Markovich: Twitter (@T_Marko), Instagram (@t_marko)

Chris Teague: Twitter (@TeagueDrives), Instagram (@TeagueDrives)

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We know you have plenty of options when it comes to products to help you with an EVAP leak. That’s why we’ve avoided jabbing you with a hard sales pitch. Instead, we’ve chosen a handful of our favorite products that have received great reviews, are reasonably priced, and that are high quality.

Got a question? Got a pro tip? Send us a note: guidesandgear@thedrive.com

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