What Is an EVAP Leak And How Do You Diagnose It? (2024)

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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.

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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.

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Featured Products

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

What Is an EVAP Leak And How Do You Diagnose It? (2024)


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

These vapors are then burned off in the combustion chamber when the engine is running. An EVAP leak occurs when these vapors escape from any part of the system. Common signs of an EVAP leak include a fuel odor, or a check engine light.

How to diagnose an evap system leak? ›

Instead, you are likely only to see an illuminated check engine light. Depending on the location of the leak and its size, though, you may smell fuel fumes. That said, using an OBD-II diagnostic scanner to read your vehicle's codes is the best way to diagnose problems with the EVAP system.

Is it expensive to fix an evap leak? ›

The national cost for an evaporative leak detection pump replacement with CarAdvise in 2024 is between $69 and $463 with an average of $202.

What happens if you don't fix an evap leak? ›

When you don't fix an EVAP problem, the check engine light will stay on, masking other problems that might occur. Of course, if local regulations require passing an emissions test, your vehicle will fail. Finally, harmful emissions are being released into the atmosphere.

What is the most likely cause of an evap leak? ›

EVAP leaks can occur for a number of reasons. The most common cause is a faulty or worn-out part in the system. This could include the fuel tank, filler cap, fuel lines, or any other part of the system. Additionally, damage to the system caused by rust or corrosion can also lead to an EVAP leak.

Can I fix an EVAP leak myself? ›

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.

What is the code for a small EVAP leak? ›

Your vehicle has a complex evaporative emissions system to prevent fuel vapors from leaking into your environment. An error code P0456 deals with this system and means there is a small leak detected.

Can you still drive with an EVAP leak? ›

That engine light on the dash may well take a back seat. After all, it could mean a lot of things, and perhaps even nothing. If it indicates an EVAP leak, then it's most likely safe for you to keep driving, but safer for you to get it fixed right away.

How much does it cost to replace an evap system? ›

The average cost for a Fuel Evaporative Canister Replacement is between $453 and $507. Labor costs are estimated between $92 and $116 while parts are priced between $362 and $391. This range does not include taxes and fees, and does not factor in your unique location.

How do you manually test an EVAP system? ›


There is a valve core under the cap, but the smoke machine should be able to push smoke right past it. If the vehicle does not have a test port, you can connect to the tank via the fuel filler using the appropriate adapter. Again, fill with smoke and check for leaks.

Do you lose gas with an EVAP leak? ›

The system is designed to capture and reuse fuel vapors; when it leaks, those vapors are lost, slightly reducing the efficiency of fuel usage over time.

How to find a large evap leak? ›

Code P0455 is typically triggered when your vehicle's computer detects a large leak in the EVAP system. Symptoms of a P0455 include a lit check engine light as well as the smell of fuel in your vehicle.

How do you test for evaporator leaks in cars? ›

To verify if a leak exists, before removing the evaporator, a vacuum test can be performed. Using appropriate flush adapters on the evaporator fittings, pull a vacuum of 28” to 30” Hg. The evaporator should hold vacuum for 30 minutes. If there is a loss of vacuum, verify that the adapters and gauges are not the cause.

How do you test an evaporative emission system? ›

To test for EVAP system integrity, the PCM runs an EVAP diagnostic monitor under certain driving conditions to detect fuel vapor leaks, and if it finds any it will set a DTC fault code and illuminate the Check Engine light.

Will an EVAP leak cause a car to run rough? ›

When the EVAP system is not functioning properly, it can cause the engine to start hard or run rough. The reason behind this issue is often a malfunctioning Purge Valve that regulates the flow of fuel vapors to the engine.


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