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Discussion Starter · #1 ·
I am not even close to being a mechanic...P0455 (M) Evap Leak Monitor Large Leak Detected A large leak has been detected in the evaporative system ....

What does that mean?


Thanks in Advance!
 

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2018 JLUR on tons and 40's.
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Sounds to me like you didn't get your fuel cap back on properly. Take it off, clean it up real good, and put it back on. Evap leaks are usually fuel related and usually lead right back to your gas cap. Clear the code before you start it up again. :)
 

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Discussion Starter · #3 ·
Thanks! I've checked the net and the consensus is that if you haven't abused your jeep lately, it's usually the gas cap....I'll try that.

How do you clear codes?
 

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pull the positive cable off your battery. Touch the positive cable to the negative terminal for 15 seconds then hook it back up.
 

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Thanks man.
I have had the same problem as you with the evap codes, small, medium, and large. I have been fighting with it since last October. I did install a new gas cap, but the codes kept coming. I would try to clear the codes by disconnecting the battery cable, then cables, for a few minutes, then a few hours, then overnight, then the positive on the negative, and everything would be good for a couple of days then on came the CEL and I would start all over again. A few weeks ago I finally got sick of it and took it to the local mechanic who advised me to take it to the stealer so they can do the smoke test, so I said ok. Well, before I left he wanted to check the code himself so he hooked up the OBD II code reader, read the codes, and cleared it out. Now three weeks later the CEL has not came back on! Maybe the new OEM gas cap fixed the problem after all? I do not know if my situation was a fluke, but the battery thing must not have worked for me, so if you have more issues with the light you may want the code cleared by a OBD II reader. Scooby
 

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The boom happens when you short the + and - terminal on the battery.... I saw my brother do that by accident a few years back. He doesn't store his tools on the battery anymore while he's working.
 

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Discussion Starter · #12 ·
Thanks for the help and suggestions everyone. I went and filled up yesterday and when I cranked it up the message was gone...I'm pretty sure i had my gas cap on crooked or something.
 

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I am having the same issues with the P0455 code. I don't see anything wrong visually looking at my gas cap. Do you recommend just changing it out for a new one? Is there a way I can check to see if my gas cap is broken?

I have gone through the tubing to the EVAP system and it looks fine. I disconnected and reconnected everything this afternoon. I am going to drive the Jeep tomorrow to and from work to get everything reset. I have the battery disconnected today.

If the code comes back after driving tomorrow, what should I look at next? Should I just take it in to the dealer at that point? Thanks!
 

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It took me a while to locate the fix as I had 455 and 138 which is a small evap leak . Its tough for a couple reasons . the vehicle only runs a Evap test every 6 or 7 starts and only when the fuel tank is a certain levels so you may try something and think you fixed it and in reality it had not run the test in a while . Do the easy things first like fuel cap and look for bad hoses in the evap system . Some places use a smoke test to locate a leak but if your large leak is as big as mine was its just a matter of looking in the right place . Mine was obvious . I looked a couple places that would of meant I got lucky but I know my luck so I removed the fuel tank early in the search and Bingo . The whole top of the fuel tank was loose . I saw it move when I dropped the tank it was that loose and that seems to be a common problem on a number of brands . Its just a big plastic ring that holds all of the fuel related items in the tank . No codes so far .
 

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I am having the same issues with the P0455 code. I don't see anything wrong visually looking at my gas cap. Do you recommend just changing it out for a new one? Is there a way I can check to see if my gas cap is broken?

I have gone through the tubing to the EVAP system and it looks fine. I disconnected and reconnected everything this afternoon. I am going to drive the Jeep tomorrow to and from work to get everything reset. I have the battery disconnected today.

If the code comes back after driving tomorrow, what should I look at next? Should I just take it in to the dealer at that point? Thanks!

It usually isn't the cap that is the problem. It is the rubber seal inside them. You should be able to remove the cap and see the seal and whether it is dirty or not. Clean it up real decent and install it again. You don't need to let the battery sit unconnected over night to reset the codes. You just need to disconnect the positive the way I described above.

There is usually nothing revolving around that code that we can not fix. The dealership is a waste of money.
 

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Ok, this is what I did the day before yesterday and then disconnected the battery to clear the code (or so I thought).

-Made sure the gas cap was on tight
-Looked at all tubing connected to the EVAP system under the hood (did not see anything disconnected, loose or any tubing broken)
-Cleaned up all the EVAP system parts under the hood to make sure there wasn't any obvious visual problems there

I thought I was in the clear and then on my way to get it re-inspected today the engine light came on with a P0455. I turned around and came back home.

What should I look at next? Should I start replacing the EVAP system parts? Do I need to remove the gas tank and look under there? I've never done anything with the gas tank so I am a newbie in that regard.

Please help, thanks!!
 

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if your large leak is as large as mine was , it really means LARGE as the whole top of my fuel tank was unscrewing itself and once the tank dropped their was no doubt where the leak was if you were within 5 foot of it a. Just the air in the tank made the lid move when you moved the tank at all , very visible . I replace the gasket which looked fine along with the evap hoses on either side of the loose ring just because I was there.
 

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I have a question about the gas cap. I pulled the O-ring off mine and it didn't look damaged. I cleaned it up and put it back with a small amount of Vaseline on it to help the seal (father-in-law suggested this). I reset the battery and will see if the code comes back in about 60 miles.

My question.....how tight should the gas cap be on there when it's in place? Mine turns until it clicks but it does move a little. Do you think this could be the cause of my P0455 code? Should I just go ahead and replace it? If so, where is the best place to get a proper replacement??
 

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I think I read some place the cap clickes 3 or 4 times to be tight . I don't know why any more than one would be needed but..... I was told to not use vasline on things like this but I can't remember for the life of me why . Might of been some sort of reaction with the rubber , can't say for sure . I have done it in the past with no bad results but stopped just in case their was some truth to it .
 
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