The Causes of an Evap Check Engine Light

One of the common causes of an evap check engine light is the tank pressure sensor, which tells the computer if the tank is pressurized or under vacuum. The vent that goes up the middle of the tank pulls the fuel vapor out of the gas tank and has a liquid vapor separator to block out any liquid fuel from getting into the fuel vapor. The fuel vapor gets stored in a vapor canister and when the right conditions exist, the computer opens up the purge valve and allows the fuel vapors to be sucked into the intake and burned during the combustion process.

The evap system also needs a fresh air source, which is provided by the vent valve. When the tank pressure sensor shows that there's a vacuum on the fuel tank, the vent valve is opened up to prevent buildup of the vacuum and keeps the system pressure balanced. The vent valve is one of the most common problems with the evap system because it's usually right under the car and exposed to all the elements. Many times, the valve gets stuck open or closed, and to fix this problem, you only have to replace the valve.

Some cars use vacuum to test for leaks in the evap system, but others actually use pressure instead. For example, Dodge, BMW, and Subaru use a pump that forces air into the tank and then sensors test for the ability of the evap system to hold pressure. There are two types of leaks: large leaks, which are usually caused by a gas cap or fuel line issues, and small leaks, which could be a pinhole leak on one of the rubber lines in the evap system.

In my case, we had a large leak, so I checked the gas cap first. To do this, you just want to turn it left and right, make sure it turns good, and then lift up. When you lift up on the bottom, you should see if it moves, but in my case, it was moving, and I actually felt like I could rip it off. So, let's take the gas cap off and see what's causing the problem.

As we look inside, we can see that the plastic in here is all broken, and it looks like the plastic that allows this to ratchet got old and brittle and broke. This is an aftermarket locking gas cap, and if you don't have a good seal, you could get a check engine light or a check gas cap light. To fix this, we need to replace the gasket. The rubber gasket here also gets brittle, cracks, breaks from use, wear and tear, and if you don't have it, the rubber bed won't seal properly.

Now, let's install a new gas cap. We can use a locking type, which is very secure and prevents theft or tampering. It's also easy to install, just like that. With this new gas cap, we should be able to fix our problem and get rid of the check engine light.

Test Drive

To make sure everything is working properly, let's go for a test drive. We'll take the car out, fill up on gas, start the engine, and see if the check gas cap light comes back on. If it doesn't, we know that our fix was successful. The first condition for the test is that the gas tank has to be between 15 and 85% full. The second condition is that there is no load or a very small load on the engine, so at low rpms, the air temperature should be between 40 and 100 degrees Fahrenheit.

If these conditions are met, the computer will perform the test once per drive cycle under certain conditions. If all those conditions are met, the computer will test the evap system, but if you don't have these conditions, the light might actually shut off, even though there's still a problem with the system.

Tip for Viewers

If you checked your gas cap and didn't think it was the problem, or couldn't find any leaks in the gasket, the next step is to check along the hose that connects to the gas tank. This is often where the connection becomes loose or the clamp digs into the rubber hose, causing a leak.

In summary, if you're experiencing an evap check engine light, one of the most common causes could be a faulty gas cap, gasket, or vent valve. Regular maintenance and inspections can help prevent these issues and keep your car running smoothly.

"WEBVTTKind: captionsLanguage: enhey guys chrisfix here today I'm going to show you how to fix a Czech gas cap light and at the same time I'm going to teach you about the evaporative system also known as the evap system if you don't have a Czech gas cap light but instead have a check engine light that has to do with EVAP system this video will teach you how to figure out what's wrong so let me give you some background on the evap system that way you understand why a car has the evap system and how it works on all 1996 and newer vehicles as well as many older vehicles you can get a check engine light or a check gas cap light if there's a leak detected in the fuel system gasoline is volatile meaning evaporates easily and that's why we have gas caps on containers of gas and also on our cars if we take this cap off and we leave it off eventually this full tank of gas will evaporate out and it'll empty completely so we make sure that we keep a gas cap on the tank and that's the same reason why we have a gas cap on our cars and our trucks it prevents the gas vapors from leaking out and since gas vapors are flammable that could be dangerous also these hydrocarbon fumes are bad for the environment so since 1971 gas tanks are sealed because the system is sealed there has to be a way to introduce air into the gas tank so while you're using your gasoline from driving around and your gas tank goes from full to empty that space where all that gas used to be has to be filled with air otherwise you'll get a large vacuum inside the gas tank and that wouldn't be good so the main idea the evap system is to prevent the gas fumes from leaking out both due to safety reasons and environmental reasons but at the same time we need to allow air to go into the gas tank to displace that fuel that is getting burnt so now we know the reason why you need to EVAP system let's go see how the evap system actually works here's what the whole EVAP system looks like so let's go break it down simplify each part we'll start with the fuel tank on the Left we have the fuel pump which feeds the gas to the engine through the fuel lines on the right we have the gas cap which seals the fuel tank and this is one of the most common causes for an evap check engine light the red sensor is the tank pressure sensor which tells the computer if the tank is pressurized or under vacuum the vent that goes up the middle of the tank is what pulls the fuel vapor out of the gas tank it has a liquid vapor separator to block out any liquid fuel from getting the fuel vapor gets stored in a vapor canister and when the right conditions exist the computer opens up the purge valve and allows the fuel vapors to be sucked into the intake and burned during the combustion process as explained before the evap system also needs a fresh air source so the vent valve is opened up when the tank pressure sensor shows that there's a vacuum on the fuel tank the fresh air prevents buildup of the vacuum and keeps the system pressure balanced the vent valve is one of the most common problems with the evap system because it's usually right under the car and exposed to all the elements many times the valve gets stuck open or closed and to fix your problem all you have to do is replace the valve one last thing most cars use vacuum to test for leaks in the evap system but some actually use pressure instead such as dodge BMW and subaru there's a pump that forces air into the tank and then sensors tests for the ability of the evap system to hold pressure now there are two types of leaks there's a large leak which is usually the gas cap or there's small leaks which could be a pinhole leak on one of the rubber lines in the evap system in my case we have a large leak so I'm going to check the gas cap here you just want to turn it left and right make sure it turns good and then you just want to lift up and I see when I lift up on the bottom here this shouldn't move and it is moving I actually feel like I could rip this right off so let's take this gas cap off and see what's causing the problem this is an aftermarket locking gas cap and if we look here you can see it's pretty much come apart looks like the plastic in here is all broken I can probably just rip this right off basically the plastic that allows this to ratchet got old and brittle and broke and that's where we're getting our air leaking in now that this is a part you could actually see the rubber gasket here this is another common problem this gasket gets brittle it cracks it breaks just from use wear and tear and if you don't have this gasket it won't seal to the surface right here so this goes in just like that so if you don't have that seal and the rubbers bed you could get a check engine light or a check gas cap light so this is going to be one of the easiest fixes I've ever done and all you need is the correct gas cap and we're going to go from this broken one to a nice brand new working gas cap I like the locking types and we could steal your gas or put anything in the gas tank that's locked in right there and we're good to go so now we'll go for a test drive okay let's go for a ride and make sure our gas cap light is shut off so the cars computer performs a test only once per drive cycle under certain conditions if all those conditions are met the computer will test EVAP system the first condition the gas tank has to be between 15 and 85% fold the test is also performed when there is no load or a very small load on the engine so at low rpms the air temperature has to be between 40 and 100 degrees Fahrenheit and if you don't have these conditions the light might actually shut off but you still have the problem and our check gas cap light hasn't come back on so I would say that is a job well done hopefully you learned a good amount about the evap system what it does what it's for and also you got to see a quick fix if this video is helpful remember to give it a thumbs up also if you're not a subscriber what are you waiting for hit that subscribe button the top tip for this video is let's say you checked your gas cap and you really don't think that's the problem you can't find any leaks in there the gasket looks good well the next thing to do is to go underneath your car you can see right there this is where we fill up that's where our gas cap is you want to check all along here and make sure you don't see any cracks in the rubber any leaks all the way to where it connects to the gas tank a lot of times the connection with a gas tank and this hose meets a clamp becomes loose or the clamp dug into the the rubber hose and that's causing it to leak and those are four major leaks so those are some other places to check if you have that lighthey guys chrisfix here today I'm going to show you how to fix a Czech gas cap light and at the same time I'm going to teach you about the evaporative system also known as the evap system if you don't have a Czech gas cap light but instead have a check engine light that has to do with EVAP system this video will teach you how to figure out what's wrong so let me give you some background on the evap system that way you understand why a car has the evap system and how it works on all 1996 and newer vehicles as well as many older vehicles you can get a check engine light or a check gas cap light if there's a leak detected in the fuel system gasoline is volatile meaning evaporates easily and that's why we have gas caps on containers of gas and also on our cars if we take this cap off and we leave it off eventually this full tank of gas will evaporate out and it'll empty completely so we make sure that we keep a gas cap on the tank and that's the same reason why we have a gas cap on our cars and our trucks it prevents the gas vapors from leaking out and since gas vapors are flammable that could be dangerous also these hydrocarbon fumes are bad for the environment so since 1971 gas tanks are sealed because the system is sealed there has to be a way to introduce air into the gas tank so while you're using your gasoline from driving around and your gas tank goes from full to empty that space where all that gas used to be has to be filled with air otherwise you'll get a large vacuum inside the gas tank and that wouldn't be good so the main idea the evap system is to prevent the gas fumes from leaking out both due to safety reasons and environmental reasons but at the same time we need to allow air to go into the gas tank to displace that fuel that is getting burnt so now we know the reason why you need to EVAP system let's go see how the evap system actually works here's what the whole EVAP system looks like so let's go break it down simplify each part we'll start with the fuel tank on the Left we have the fuel pump which feeds the gas to the engine through the fuel lines on the right we have the gas cap which seals the fuel tank and this is one of the most common causes for an evap check engine light the red sensor is the tank pressure sensor which tells the computer if the tank is pressurized or under vacuum the vent that goes up the middle of the tank is what pulls the fuel vapor out of the gas tank it has a liquid vapor separator to block out any liquid fuel from getting the fuel vapor gets stored in a vapor canister and when the right conditions exist the computer opens up the purge valve and allows the fuel vapors to be sucked into the intake and burned during the combustion process as explained before the evap system also needs a fresh air source so the vent valve is opened up when the tank pressure sensor shows that there's a vacuum on the fuel tank the fresh air prevents buildup of the vacuum and keeps the system pressure balanced the vent valve is one of the most common problems with the evap system because it's usually right under the car and exposed to all the elements many times the valve gets stuck open or closed and to fix your problem all you have to do is replace the valve one last thing most cars use vacuum to test for leaks in the evap system but some actually use pressure instead such as dodge BMW and subaru there's a pump that forces air into the tank and then sensors tests for the ability of the evap system to hold pressure now there are two types of leaks there's a large leak which is usually the gas cap or there's small leaks which could be a pinhole leak on one of the rubber lines in the evap system in my case we have a large leak so I'm going to check the gas cap here you just want to turn it left and right make sure it turns good and then you just want to lift up and I see when I lift up on the bottom here this shouldn't move and it is moving I actually feel like I could rip this right off so let's take this gas cap off and see what's causing the problem this is an aftermarket locking gas cap and if we look here you can see it's pretty much come apart looks like the plastic in here is all broken I can probably just rip this right off basically the plastic that allows this to ratchet got old and brittle and broke and that's where we're getting our air leaking in now that this is a part you could actually see the rubber gasket here this is another common problem this gasket gets brittle it cracks it breaks just from use wear and tear and if you don't have this gasket it won't seal to the surface right here so this goes in just like that so if you don't have that seal and the rubbers bed you could get a check engine light or a check gas cap light so this is going to be one of the easiest fixes I've ever done and all you need is the correct gas cap and we're going to go from this broken one to a nice brand new working gas cap I like the locking types and we could steal your gas or put anything in the gas tank that's locked in right there and we're good to go so now we'll go for a test drive okay let's go for a ride and make sure our gas cap light is shut off so the cars computer performs a test only once per drive cycle under certain conditions if all those conditions are met the computer will test EVAP system the first condition the gas tank has to be between 15 and 85% fold the test is also performed when there is no load or a very small load on the engine so at low rpms the air temperature has to be between 40 and 100 degrees Fahrenheit and if you don't have these conditions the light might actually shut off but you still have the problem and our check gas cap light hasn't come back on so I would say that is a job well done hopefully you learned a good amount about the evap system what it does what it's for and also you got to see a quick fix if this video is helpful remember to give it a thumbs up also if you're not a subscriber what are you waiting for hit that subscribe button the top tip for this video is let's say you checked your gas cap and you really don't think that's the problem you can't find any leaks in there the gasket looks good well the next thing to do is to go underneath your car you can see right there this is where we fill up that's where our gas cap is you want to check all along here and make sure you don't see any cracks in the rubber any leaks all the way to where it connects to the gas tank a lot of times the connection with a gas tank and this hose meets a clamp becomes loose or the clamp dug into the the rubber hose and that's causing it to leak and those are four major leaks so those are some other places to check if you have that light\n"