Check Engine Light? Codes P0446, P0455: What Causes a Car EVAP Code?

EVAP Explained! It's one of the most common OBDII trouble codes, thanks to loose or leaky gas caps, vent valves, purge valves, and solenoids. But did you ever wonder why? In this video, Any goes to the white board to explain the EVAP system, what parts throw those DTC codes, and why.

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While 1A Auto strives to make the information provided in this video as accurate as possible, it makes no claims, promises, or guarantees about the accuracy, completeness or applicability of the content. No information contained in this video shall create any expressed or implied warranty or guarantee of any particular result. All do-it-yourself projects entail some risk. It is the sole responsibility of the viewer to assume this risk. 1A Auto is not responsible or liable for any loss damage (including, but not limited to, actual, consequential, or punitive), liability, claim, or any other injury or cause related to or resulting from any information posted in this video.

[AAuto]

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[titodarden]

My wife has a 2004 Pathfinder and she got a p0455 code (evap gross leak, large evap leak). Took to the dealer, they changed charcoal canister, vent valve, purge valve. Then p0455 code went away, then we got p1456 code (small evap leak). Dealer then changed gas cap, still got p1456 code. Took back to dealer after 1 month, they charged $185 diagnostic fee, said it was stuck vent valve. I researched, bought new fuel tank pressure sensor and vent valve. I installed both, still got p1456 code. On my work day off, I got under car, removed canister (I tested it, good). I noticed rubber hose coming from gas tank to canister was stretchy, so I bought new fuel hose. I cut back a little bit of the purge line rubber hose (it was stretchy). Also I bought new clamps (ones where you use screwdriver to tighten). Installed the new fuel hose (that connects to the canister), 3 new clamps for the 3 hoses that attach to the canister (vent, purge and fuel). Bingo!!! No more codes pop up (no more CEL check engine light). No more evap leaks. Hope this helps somebody.

[Bohminator]

Before you replace the valve or other components check your lines! lines are known to crack and dry rot and it will be a lot cheaper to fix.

[gwendolynfloccari]

Great info. Calm clear description. I'm 75 year old woman trying figure out problem with my car. Mechanics charge so much so want to informed before take my car in. Wish I could still do simple maintenance one my car.

[Txi-brwb]

This is the best and clearest explanation I have seen of this. Thank you!

[jbarnes]

Love your videos. You explain them in every day terms and do not make us feel inferior because of our lack of knowledge. Keep up the great work.

[r.j.hadameo]

Awesome video, I was in the Automotive field for 25 years, mostly sales, but your videos always are easy to understand and always right on the money for the diagnostics he talks about.

[hillcountrygarage]

One more tip on the gas cap, make sure it is clean and free of debris. If it's a bit dirty, just get some alcohol wipes and clean both the inside of the cap and the rim of the filler neck. That is one of the most common problems I've seen with the P0440 code

[boomertsm]

Last week, I got a PO446 code on my 2011 GMC Terrain 3.0L, Took it to my repair shop. They used smoke to identify an evap leak coming from my gas cap, so I ended up paying them $62 for a new gas cap, $220 overall for the repair (labor, part, and Credit Card processing fee!. After one week, the code reappeared, so I'm going back to the shop to see if the leak is coming from the gas cap area or other places. Thanks for the video. Well done.

[dinonaccarato]

Just a note,
You guys at 1A auto are definitely, #1A.
I disassembled my 350 to remove my heads and assembled it just but watching your video.
Just recently I watched the video for Evan code and again. Simple and thorough.
Thanks guys
Dino
Edmonton, Ab.
Canada

[michaelballard]

This video explains a lot. I had 2 different shops that did smoke test, and neither could find it. The last shop suggested going to the dealer. I have a 2010 Jeep Grand Cherokee, and experience with what may be causing this small leak on this type of vehicle. Code is a po456. Some type of pump was replaced, which in this video I didn’t see or hear about a pump. It was done before the smoke test. I think the pump and labor was under 100, and they told me it may or may not be the problem. 2 smoke test later, I still have a problem.

[cristianbivolan]

As an old, retired electrical engineer I am very impressed with your teaching skills. Repairing my cars is one of my hobbies, but sometimes I am getting stuck into hidden specific manufacturing problems, like a fuse found under the wax paper insolation on a small AC transformer. Anyhow, I would greatly appreciate if you could help me troubleshoot my 2003 BMW 745Li, which started with not accepting more than 1/2 tank fuel (except when dispensing very, very little at the time), and lately getting the so popular check engine light on with the P0444 code on it. I disconnected and tested the purge valve and seems to be perfectly fine, opening and closing promptly when applying 12v to it. It may be that the purge valve intake hose having a small leak at the connection to the other hose going to the charcoal canister is triggering the P0444 code, but I do not believe this has anything to do with the tank not accepting more than half fuel. BTW, there is no pressure, nor vacuum at the filling cap after driving the car. Could you please feed back with your expertise/experience on this?
Thanks a million,
Chris

[madchilll]

this was the most soothing and informative video.... came here to learn about the EVAP system, subscribed for the guy’s voice and great presentation. so chill! thank you!

[austinhunt]

I love 1a auto, these are the exact the videos I look for when in need of help fixing my own vehicle

[bigrad]

Thank you for this simple and easy and right to the point video 👍

[josiah]

Diesel very good tips for checking the evap system on a car, however… I ran into the trouble of replacing the filler neck on my 04 trailblazer… using a Dorman part… come to find out these Filler necks do not seal to the GM gas cap.. took me a whole year to figure out what was wrong…. I could not find anyone who could check my gas cap for me…… I purchased another neck thinking I had a defective one as well as two caps…. When I attempted to apply pressure orally to the filler neck and found the gas cap leaked as if it was an open vent is when I realized I needed the factory jam part filler neck… and that’s how I got my check engine light off and cleared for inspection

[mrtrillionfold]

Thanks for the Video. It helps to easily understand the EVAP system.

[everettbillingslea]

Extremely helpful. Now I know where to begin in solving my problem. Without this understanding it was hard to know where to begin.

[thomaslaban]

I found it easier to take the bolt out and then remove the connections. Good video, helped me out.

[marshmower]

I may have a leaky tank hose or breather. My gas cap used to go "pshh" when i removed it. No more. Evap solenoid alows flow when energised. Blocks flow when disconnected. I just unplugged it and the breather line. I no longer smell gasoline either when i stop. Gas mileage went up 5 mpg... I believe it was sucking lots of air through the tank somehow.