How the EVAP System and Gas Tank Work

Here's how the Evaporative emissions system work on a modern automobile.

The purpose of the EVAP system is to control the release of gasoline vapors entering the atmosphere, causing smog. It is a self-governing, mandated system that vents most harmful vapors into an external charcoal canister for refinement.
The system consists of several components: The gasoline tank, the fuel sending unit, temperature sensor, pressure sensor, vent and purge solenoids, charcoal canister, vacuum hoses, filler neck, gas cap and fuel check valve inside the tank.

When gasoline is being filled into a tank, vapors are routed to the charcoal canister for refinement. Air and water vapor are allowed to vent to atmosphere, allowing the tank to fill up seamlessly without trapping air.
During normal vehicle operation, gasoline vapors are routed to the charcoal canister and then sent to the air intake through a vacuum hose. The engine then reburns this vapor, with the ECU compensating accordingly for a richer mixture. The release is controlled by the purge valve.

A pressure sensor situated on the purge line (near the charcoal canister) allows for self regulation of the EVAP system through OBD2 protocols. During certain drive cycles, the ECU can detect if there is any leaks in the EVAP system and throw a check engine light accordingly.
It does this by drawing a vacuum on the system from the air intake, then sensing if there is any pressure drops (and the extent of the drop) due to a leaking system.

In this video, the entire EVAP system is gutted from an Infiniti G35, cut open, cross-examined and explained. The gas tank is cut open to examine the vapour cut off and liquid recovery floats, the dual-tank like system (due to RWD configuration) and the valving inside the filler neck.
Furthermore, the EVAP canister and vent valve is cut open to examine its role in the system.

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[MichaelAChang]

3 classroom lessons wrapped up in under 14 minutes - nice job.

[johnfearn]

Every time I watch your videos I learn something new. I never knew a fuel system was so complicated. Thanks for explaining it all so well.

[tankeryanker]

As a trucker, I roll into different job sites with different jobs and always running into new and unfamiliar jobs. I always tell the clients to explain it like I’m a 2 year old lol. You truly have a gift

[fernandoanatomia]

Always wanted to understand how this system works. This channel is a gold mine. Thank you for sharing such great content!

[hestheMaster]

Your explanation of how a fuel system works and showing cut outs is excellent. Safety first in cutting open a fuel tank, which most people never get to see is
super cool!

[SerandibBroadcast]

I got to know this channel very recently. Have to say sir, this is very informative and educational for everyone. I drive my car daily without knowing any of this. You are not just uploading some video content, rather teaching thousands like myself. Thanks and keep up the good work.

[pbierre]

This is a good tutorial on the pre-2006 OBVR design. The next generation design, EVR Phase 2, adds a Refueling Vent Pipe directly returning vapor from the tank to the filler throat during fueling. The EVR Phase 2 gas-pump-nozzle adds a return path for fumes, suctioned into a small orifice (3mm) on the nozzle. In EVR Phase 2 vehicles during refueling venting DOES NOT depend on the path through the CC (as it does in older OBVR cars).

[joshhayes]

I'm pretty sure you've just coined the term "an incision with an angle grinder" :) I've always wondered about the evap system, great explanation, thanks!

[LoganTanner]

This video was amazing. Huge props. I noticed super high pressure in the gas tank of my 2001 Toyota Sequoia yesterday after a drive in the mountains. My research points to the EVAP system, so thumbs up for this incredibly detailed and hands on video explaining the whole thing and where and why faults happen. Off to watch you video on the Toyota EVAP system now.

[chrisbrowning]

The most concise, effecient, and informative thing I've seen in my life. Amazing video, thanks for uploading!

[bobbykeyz]

So I had a tighten gas cap on my Tahoe. I changed the gas cap and reset my check engine light. A few days later, it said it again, and my check engine light came back on. I needed to learn more about this evap system. I have to say you explained it better than any other YouTube channel. Thank you. You just got another subscriber.

[solarflare]

You should be in a Mechanic Institute teaching how to do things the proper way. Great video.

[Emils]

I always think, I know everything, and then I watch your video and understand that I don't know anything

[alm]

very good description of how the system works. I have cleaned many canister control valves because they were full of dust. (several table spoons full from most of them) I've seen the vent hose full of tiny pebbles too. This is common when you drive on gravel roads.

[davidellett]

Excellent! This is the way videos should be done. Diagrams, parts cut open, detailed explanations without wasting even a second of time. So much so that I had to repeat a couple parts that I did not understand. But that's perfectly okay, I don't want other peoples time wasted while having to wait for me and vice-versa. Perfect!

[jamesvisocky]

Thorough, articulate and well explained. I especially like seeing the parts cut open and cross-referenced with diagrams. This answered my question about what the canister is for plus how the whole evap system works, since the canister isolated from everything else would not make a lot of sense. Great job!

[ibrahimeltony]

Excellent 👍
One cannot explain more the fuel EVAP system like this.

[earldaisgomez]

Dear sir. Greetings.
Sir. You're not only a EVAP System doctor but also a Experienced Surgeon.

[mattmcgyver]

This just saved me a huge mess of diagnosis on my G35. I could not find out anywhere how this worked let alone what it looked like. You are straight up my hero, thank you so much.

[timothyalan]

Amazing attention to detail, incredible explanation, and very thorough. Not only am I impressed with the depth of your knowledge, I'm in awe at how interesting the inner mechanics of a vehicle are. Great video, one that I'll revisit to reinforce the information presented. Thank you for potentially saving me a lot of money.