So you're driving along and your check engine light pops up.
You scan it, and you find that you have an EVAP code.
What does that mean?
First, you need to know what the EVAP system does.
It's part of the emission system that prevents fuel vapors from entering the atmosphere.
Here is how most of the systems are set up.
Some components may be in a different structure, but the basics are the same.
You all have the fuel tank, and you have the fuel vapors.
You have a gas cap.
You have the EVAP canister.
You have an EVAP vent, and you have a purge solenoid.
And then this would be where it connects the engine on the intake side.
And also there may be a pressure sensor in the fuel tank, different vehicles have them
in different places, sometimes they may be over in this line or part of the vent.
When the car starts and it wants to engage the EVAP system, what it's gonna do is send
power and ground to the vents, which is normally open, and it's gonna close that vent, and
the vapors are in this area, you wanna keep them out of getting out of the gas cap.
They're gonna go through the charcoal canister, but we wanna put a vacuum on this system.
So the computer is gonna command on this purge valve, which is gonna open.
Normally the purge valve is closed, that we'll open, and we're gonna have a vacuum, going
towards the intake, and it's gonna pull the fuel vapors into the canister.
This valve will be closed at the time, and it's gonna monitor the vacuum in the system
to make sure that you don't have any leaks.
This will close eventually, and with the vacuum in the system the computer is gonna monitor
how long it can hold that vacuum.
And if it can't hold the vacuum, then you're gonna get your check engine light.
So if you have a leak, the first thing you wanna check is the gas cap.
Unless you have an EVAP circuit code, it's always best to start at the gas cap.
Just grab the gas cap, try to pull on it to see if it's completely loose, and then loosen
it up, check the seal.
See if it's dry rotted, if it is, it's gonna need to be replaced.
And also check the ratchet part of it, if it clicks or if it doesn't click, however,
the gas cap is set up, if it's really loose, then it's probably not tightening down and
you could have a leak there.
The other two problems that are pretty common on most vehicles, because they're the only
moving parts in the system is the vent and also the purge valve.
Most vehicles the purge solenoid is gonna be somewhere near the intake, it'll be a valve
like this.
There'll be wires connected to it.
This hose goes to the back of the vehicle, and this hose right here goes to the intake
itself.
One way to test if this valve is actually closing, you can take a vacuum pump, put a
vacuum on it, it should stay.
And it looks like it's holding, which is good.
If you have the ability to take the scan tool and open the valve, you can plug this back
in, have the scan tool, open the valve, and see if it goes to zero.
Somewhere near the fuel tank, you're gonna have the EVAP canister or the charcoal canister.
It's located right here, and near that is gonna be the vent valve.
To check that, the best way to do it is to command it on and off with a scan tool, and
see if it opens and closes.
So these are the three most common problems: the purge valve, the vent valve, and the gas
cap.
Those are the three moving parts.
These other components, you could always have a leak in the gas tank if the fuel pump or
anything is rusty, lot of times those are gonna leak.
It's hard to find a leak if it's not one of those items.
You can be creative, sometimes soapy water works if you spray something down, it's gonna
be hard to pressurize it.
But I've seen just the natural pressure of the gas tank cause bubbles from the soapy
water.
So that's one way.
When at the dealership or most automotive repair places, they use a smoke machine, and
they pour smoke into here and try to find the leak.
It's not that easy to find that way either, but be creative, take a look at any of the
lines, and if you see anything obvious, that's the most easy way to do it.
I hope this video helped you out understanding how EVAP systems work.
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