Vehicles are complex machines with a lot of moving parts and systems that help create the perfect blend of power and function. Whenever something goes wrong with your car, it’s important to figure out what the issue is and find a resolution as soon as possible. In this guide, we’ll discuss the evaporative emissions system, including what it does and why you need it, as well as whether it’s worth the repair (spoiler alert: it usually is). 

After all, the average rate for repairs of the evaporative emissions system, also called the EVAP system, ranges from $200 to $560, which is a small price to pay to fix a Check Engine Light when you consider all the possibilities. 

What is the Evaporative Emissions System?

In modern vehicles, the Evaporative Emission System is responsible for storing and disposing of fuel vapors as they make their way to the atmosphere. This helps reduce the number of emissions coming out of the vehicle, which helps the environment. It also increases the fuel efficiency of a vehicle and ensures that the cabin doesn’t smell of gas. 

These systems are designed to protect you (and the environment) from fuel vapors. There are several different types of systems out there that fit different vehicles and types of automobiles. The standard system includes:

• Fuel tank: This is what stores the fuel until it’s needed by the engine. The tank is designed with airtight seals and valve access points to ensure that fumes and fuel don’t leak out. It can also hold a small volume of vapor before delivering it to the storage canister. 
• Gas cap: The gas cap is a lot more critical than people realize. If they aren’t properly calibrated, designed, and installed, they can cause the vehicle to display an immediate warning to the driver. Gas caps come in two styles: vented and non-vented. You will need to have yours replaced with the appropriate model to restore the EVAP system if this is what is causing the issue. 
• Canister purge valve/solenoid: This is an electrically operated valve that is designed to open the engine and create a vacuum to draw in vapors from the EVAP canister. If the valves are clogged or held open by debris, this could result in a faulty system and a “Check Engine” light coming on. The cleaning of the system will resolve this issue. 
• Fuel tank pressure sensor: As mentioned, the pressure of the fuel tank and fuel system are integral to its successful operation. The pressure sensor is what reads and monitors the pressure throughout the system. If a leak is detected, the PCM will send a code to the OBD and cause the dashboard’s engine light to appear. 
• Fuel pump: Modern fuel injection systems operate under high pressure. On vehicles with an OBD II, the PCM is responsible for controlling the power to the fuel pump and making sure it operates properly. When the fuel pump is faulty, it causes low system pressure if it is faulty, or the electrical connections are bad. If there are defective clogs or regulators, that can also lead to low pressure. High pressure can occur as a result of a defective pressure regulator or restricted return lines. 
• EVAP canister: This is a rectangular piece mounted somewhere that is filled with activated charcoal. It is designed to absorb and store vapors from the fuel system. When the engine is being engaged, the PCM opens the purge valve, and the vacuum draws vapors into the engine before sending them out as emissions. If this canister is leaking or there’s a faulty purge control, it may need to be repaired or replaced. 
• Tubes and valves: Every fuel system and emissions system is filled with fuel lines, tubes, and vales that are responsible for transporting fuel and vapors throughout the system. If any of these become defective, develop a leak, or are otherwise faulty, it could generate a lot of problems for the EVAP system. 
• Leak detection pump: In some vehicles, there is a leak detection pump that helps monitor the system and ensure that the pressure remains the same. A pressure drop usually indicates a leak, allowing this pump to figure out where electrical issues exist, or other things might be going wrong. 
• PCM: Also known as the Powertrain control module, this is responsible for checking the EVAP system and its integrity, as well as metering stored vapors during certain operating conditions. The PCM will run a diagnostic monitor to detect leaks of fuel or vapors. If it finds any leaks, it will create a fault code that causes the “Check Engine” light to illuminate. If the PCM is faulty, it could be related to bad oxygen sensors or an entirely damaged PCM, which generally results in expensive repairs.  

All of these elements work together to get rid of the harmful emissions coming from the engine. If the fuel system is left open to the atmosphere, it will be able to pollute the air 24 hours a day with evaporative fumes and emissions even if the vehicle isn’t running. By having a properly functioning EVAP System, gasoline vapors won’t escape from the fuel system and tank into the atmosphere until they are filtered through the engine and mixed with fresh air to reduce the impact of the emissions. 

What is an EVAP Leak?

An EVAP leak is a leak that is found in the EVAP system, which can be caused by any number of things. Something as simple as a loose gas cap can trigger the “Check Engine” light, so it’s important to check the obvious before you spend a fortune on a diagnostic scan. Because there are so many moving parts to this system, there are several ways that a leak could happen. Even a hole as small as a needle can cause the system to malfunction and generate the dashboard light, so the system must be properly inspected and repaired. 

A leak can occur in several different parts of the evaporative emissions system. As mentioned in the description of the various components above, any malfunction that results in a leak will put the system in a compromising position. Therefore, it should be fixed right away. That starts by finding a reputable shop that knows how to work with EVAP systems and provides the best solution that doesn’t break your budget. 

A visual inspection will usually be required to investigate the full extent of the leak or damage that is present. This is a complicated network of valves, hoses, filters, and components and there could be any number of issues present. Fortunately, the OBD II should be able to help diagnose exactly what’s going on by providing a DTC code. Considering that there are hundreds of reasons the “Check Engine” light may come on, these codes can be invaluable. 

If you have a light on and you think it’s related to a leak in your Evaporative Emissions System, it’s time to get it checked out. Contact a qualified mechanic right away and have your vehicle tested to find the problem and get it fixed as soon as possible. Otherwise, it could lead to issues beyond poor emissions and a less smooth engine operation. 

How is an EVAP Leak Fixed?

The way that a leak is repaired depends on the leak itself. For example, in the case of a loose gas cap, simply tightening the cap will cause the light to go off. Of course, not all leaks are so easy to find or fix. The technician will perform an OBD test to identify which codes are being generated so that they know where to begin their search. 

Typically, you can tell that you have a leak if there’s a smell of gasoline or if you experience: 

• A drop in engine performance
• Rough idling
• Poor fuel economy
• Trouble getting the car to start

Once they know the issue at hand, they will have a better idea of where to start. Then, they will start inspecting all of the various elements that could be at fault until they find the cause of the leak. Once they figure out the cause, they will have any number of solutions to fix the leak, including plugs, new hoses, replacing parts, and more. Today’s OBD codes are pretty good at getting to the heart of the problem. 

Unfortunately, some people feel that they’ve got issues present that aren’t worth fixing because it could take so long to get to the root of the issue. These people will be happy to know that this is rarely an issue anymore. Reputable and experienced mechanics will have no trouble figuring out exactly where the EVAP system is leaking or has otherwise failed and coming up with the best solution to resolve the issues. 

What Else Can Go Wrong in the EVAP System?

Beyond leaks, EVAP systems have also been known to see blocked vents, bad purge flows, and other issues that result in a faulty system. There are so many moving parts in this sealed system and sometimes things will eventually fail or require replacement. When the EVAP system fails, a “Check Engine” light will appear, and a specific code will be attached to the problem based on what is wrong. 

Blocked vents mean that airflow is not getting through, and emissions are building up in the filters and the system itself. That can prevent the system from working effectively or even cause the cabin to smell like fuel. 

Essentially, you can see all the potential ways things can go wrong when you see how these systems actually work. For starters, when the fuel in your tank evaporates, the vapors are contained by a charcoal canister in the front of the vehicle. Once the fuel-air mixture is normal, it goes back to the engine. Then, the valve creates a vacuum and draws all the vapors into the engine. Those vapors combine with fresh air to create a more efficient combustion process. 

Depending on the age of the vehicle, the process will either be controlled mechanically or by a computer. Any number of these control components could cause issues that result in a faulty EVAP system, and that could easily create bigger problems if you don’t address them right away. 

How to Find Repair Assistance

The solution to all of your Evaporative Emissions System issues is to rely on the trained expertise of a local independent shop that can help you identify exactly what is going on. When researching your options, make sure that you check for shops that have experience with EVAP systems and their functioning so that you get the best repairs from people who know what they’re doing. 

Even if you aren’t noticing any operational issues (or that many of them) because of your EVAP system issue, it still warrants fixing. For starters, it will ensure that your vehicle is running as smoothly as possible. It will also guarantee that you’re not emitting too much pollution into the environment and that you won’t be creating bigger problems down the road by letting a “simple” issue like this go. Check engine light issues are scary and can be overwhelming, but when it comes to your EVAP system, you’ve got to address the issue head-on to get things resolved and protect your vehicle. 

Furthermore, if you live somewhere where emissions tests are required, a “Check Engine” light is going to automatically cause you to fail this test. Thus, you may not be able to pass an emissions check and renew your vehicle registration if you have emissions system issues. Even if you’re not in it to take care of the vehicle, do it so that you can keep driving your vehicle legally. 

When you’ve got a reputable independent shop that you can rely on, you’ll be able to get quick, affordable solutions no matter what’s up with your EVAP system. Diagnosing the problem(s) and finding the right solutions will ensure that your vehicle is operating at its peak performance and that you’re not polluting the environment any more than necessary. 

Resources

https://www.ferberstireandauto.com/blog/how-does-the-evaporative-emission-system-evap-work

https://www.nyvip.org/PublicSite/OBDII/evap.html

https://www.autoselectonline.com/article/evap-system-top-5-reasons-for-a-check-engine-light-to-come-on

https://www.nadaguides.com/Cars/Shopping-Guides/what-is-an-evap-leak 

https://denverexpresscare.com/evap-system-leak-now-what

https://howtodiscuss.com/t/evap-leak-cost/55944

https://autoservicecosts.com/evap-system-repair-cost/