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Discussion Starter #1 (Edited)
My CEL (check engine light) came on this past Monday and I checked for codes with the three key turns method and got P0456. When I looked it up it said:

Evaporative Emissions System - Small leak detected

What does that mean?
The Powertrain Control Module (PCM) at different times performs various tests on the EVAP system. OBD II Enhanced EVAP systems are in place to keep fuel tank vapors from venting into the atmosphere, and instead purges them into the engine to be burned. Regular pressure tests are conducted by the PCM to monitor the sealed system for leaks. The PCM monitors the EVAP system pressure by watching the Fuel tank pressure sensor (FTP). When the sensor indicates a small leak in the EVAP system, this code is set.

Potential Symptoms
There will likely be no noticeable symptoms other than the Malfunction Indicator Lamp (MIL). This is because the EVAP system is a closed system and only controls fuel tank vapors, not engine management.

Causes

Usually this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could conceivable cause this code as well or if the cap wasn't properly tightened. Any of the following could also be the cause:
  • A small leak in any of the EVAP hoses or fuel tank hoses
  • A small leak in the purge valve or vent valve
  • The EVAP Canister may be leaking
So I checked the gas cap and still got the code and the CEL has been on all week. I filled up my tank today and the CEL went out. ????????
 

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Full tank = No or low vapors. If it's not the cap it will probably come back on.

How did you check the cap? I've seen the cap seal get twisted before and adjusting has cleared the problem.
 

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Discussion Starter #3
Full tank = No or low vapors. If it's not the cap it will probably come back on.

How did you check the cap? I've seen the cap seal get twisted before and adjusting has cleared the problem.
I took it off and put it back on several times. It seemed to be fitting ok.
 

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I had this issue many times. 1st time at the shop they inspected and tighten hoses. The second time the gas cap was replaced (i was very doubtful). It's been quite a while since I've had another 0456 (had one since the cap was replaced). Overall the repair was effective IMO despite the single occurrence.
 

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Check engine light repeatedly comes on.....

...then goes off after a few days. No noticeable change in performance, MPG, etc. - only that dreaded light is on. I have noticed it is usually a few days after I fill up. It will come on when I get to around 2/3 to 1/2 tank, stay around for a few days, then one morning its gone until the next fill up. I've done the three key turns and get "P 0456" on the display, which I think is a misfire, reading IIRC. Have never received a notice that the gas cap is loose. Any ideas????
 

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Discussion Starter #6 (Edited)

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Moved your question to the linked thread.
 

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I had the same problem with 2006 scion Tc. Check engine light came on flagging my EVAP system. Everytime I checked the gas cap it seemed tight. I chose to replace the gas cap because it was cheap. Once the cap was replaced, I cleared the code by disconnecting the neg. battery terminal for about 2 mins, and it has been going good ever since then, about 5000 miles now.
 

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Doesn't the Jeep have a message that says "tighten gas cap" in the display?
 

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I just got the same code on my '08 Commander. P0456 Checked the gas cap (looks good) and filled the tank. light is still on.
I'm gonna try to get it to the dealer next week, but just want to make sure I'm understanding the warranty correctly.
Pretty much anything in the EVAP system should be covered under warranty right? The truck has 18K miles and was purchased new 13 months ago.
Thanks
 

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P 0456

...then goes off after a few days. No noticeable change in performance, MPG, etc. - only that dreaded light is on. I have noticed it is usually a few days after I fill up. It will come on when I get to around 2/3 to 1/2 tank, stay around for a few days, then one morning its gone until the next fill up. I've done the three key turns and get "P 0456" on the display, which I think is a misfire, reading IIRC. Have never received a notice that the gas cap is loose. Any ideas????

Help.. I have this same problem. How did you resolve it? Thanks.
 

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Sounds like a lot to do with the gas cap. I dont know the answer to your question but I have heard some guys went to dealer and bought a new gas cap and that fixed the problem. Worth a try I guess unless someone else chimes in.
 

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OBDII is a Federal Requirement that the Engine Controller test the vehicle and make sure all the pollution control equipment is working properly.

The Fuel system has to be sealed against raw fuel fumes escaping, as the fuel fumes build up, the Evaporative Emmissions system stores the fumes and then occassionally burns them in the engine to get rid of them.

OBDII has to test this system, as well as the others, to make sure it is working correctly. The Federal Standard is set at, if a leak is detected equalavelent of a 200 micron hole, it fails.

The way this test is performed by the vehicle, is engine vacuum is applied to the EVAP system and its seals off, and they wait for vacuum to leak down. There is no pressure sensors in the system, it works off a several calibrated spring loaded valves that will pop open at certain vacuums/pressures, and the PCM is signaled when the valves open and close, with the PCM timing how long it takes for the valves to pop open. Other systems use pumpe to increase pressure in the system, and the pumps are usually vacuum driven, with the PCM monitoring the pump up times to deduce if there is a leak or NOT.

The test is usually only performed when the engine has been cold soaked overnight, the temps are below a certain level, and fuel level is between a certain amount. So, if you fail the test, it could be a few days to a few weeks before the vehicle will perform it again and if you pass, it will turn out the light.

The Gas Cap is being taken on and off all the time, and sometimes folks don't pay attention and do NOT put it on correctly, and it doesn't seal perfectly, it will create that tiny leak that will fail the evaporative emmissions system. That is why the code is listed with the advice to check the gas cap, you could have a perfectly good system, and the owner messes up putting on the gas cap, and that will cause the system to fail the test. Reset the gas cap and seal it properly, then the next time, it could very well pass the test.

OR, there could be something wrong with the system and it wasn't the gas cap as the cause. Unfortunately, it could take a couple of weeks before the system runs the test again.

All the manufacturers have been having trouble with this system, and especially reapairing it. The system leaks nothing, the mechanic can't find anything wrong, and it still fails, throw ontop of that, the test won't re-run for days to weeks, it really drags out the repair. The standard for the leak is so incredibly high, perfectly good system can fail for just be slightly degraded or slightly out of calibration. Often the mechanics are left with playing parts jepordardy, just replacing a part each time it fails, hoping that they magically guessed the right part this time.
 

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I'm bringing back a fairly old thread, but I figured I'd keep my related issue here instead of starting a completely new thread. I've also done a search and read thru this thread - https://www.jeepcommander.com/forums/5-general-commander-discussion/11096-need-favor-re-gas-cap.html and it has some good info in it related to what I'm working on. Hopefully someone here can give me some direction specific to my situation. Thanks in advance.

I've had my check engine light on for a while now with the "P0456 - Small Emissions Leak" code. A while back I replaced the gas cap, with this one from Amazon https://www.amazon.com/gp/product/B0049ELS54/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
That didn't turn the check engine light off. I have also recently replaced the Vapor Canister Purge Valve under the hood. At that time we inspected the lines under the hood connected to the valve and they appeared to be good (not sure exactly how to be sure, besides seeing any visible cracks / holes, etc or doing a smoke test). I drove around for about a week and the check engine light didn't go off automatically. My brother has the code reader that can reset the check engine light. So this past Thursday we reset the light and it was good for a few days, but it came back on today.

I've been reading up on this a bit, after what I've already replaced, it looks like the items left that could be causing this leak are the Charcoal Canister, the filler neck on the gas tank, maybe a gasket between the filler neck and the tank and also the lines that connect all of these components?? I've also read that you should get the gas cap directly from the dealership (so that is another possible piece)?? After a bit of googling I came across a PCV Valve - https://www.justforjeeps.com/37l47lpcvvalve.html but I'm not sure if this would be related at all?? I feel a bit like the more I search the more suggestions I get for replacing parts.

I'm trying to work thru and replace as many of the cheaper / easier to replace items first. My thought would be that I'd replace the Charcoal Canister next and then leave the lines and pieces connected to the gas tank for last as I'd think they'd be a bit more difficult and costly??

Again I'm just hoping to get some input to make sure I'm on the right path as I slowly replace these pieces. And to make sure I'm not completely missing a component of the system to look at. Thanks again.
 

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I'm bringing back a fairly old thread, but I figured I'd keep my related issue here instead of starting a completely new thread. I've also done a search and read thru this thread - https://www.jeepcommander.com/forums/5-general-commander-discussion/11096-need-favor-re-gas-cap.html and it has some good info in it related to what I'm working on. Hopefully someone here can give me some direction specific to my situation. Thanks in advance.

I've had my check engine light on for a while now with the "P0456 - Small Emissions Leak" code. A while back I replaced the gas cap, with this one from Amazon https://www.amazon.com/gp/product/B0049ELS54/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
That didn't turn the check engine light off. I have also recently replaced the Vapor Canister Purge Valve under the hood. At that time we inspected the lines under the hood connected to the valve and they appeared to be good (not sure exactly how to be sure, besides seeing any visible cracks / holes, etc or doing a smoke test). I drove around for about a week and the check engine light didn't go off automatically. My brother has the code reader that can reset the check engine light. So this past Thursday we reset the light and it was good for a few days, but it came back on today.

I've been reading up on this a bit, after what I've already replaced, it looks like the items left that could be causing this leak are the Charcoal Canister, the filler neck on the gas tank, maybe a gasket between the filler neck and the tank and also the lines that connect all of these components?? I've also read that you should get the gas cap directly from the dealership (so that is another possible piece)?? After a bit of googling I came across a PCV Valve - https://www.justforjeeps.com/37l47lpcvvalve.html but I'm not sure if this would be related at all?? I feel a bit like the more I search the more suggestions I get for replacing parts.

I'm trying to work thru and replace as many of the cheaper / easier to replace items first. My thought would be that I'd replace the Charcoal Canister next and then leave the lines and pieces connected to the gas tank for last as I'd think they'd be a bit more difficult and costly??

Again I'm just hoping to get some input to make sure I'm on the right path as I slowly replace these pieces. And to make sure I'm not completely missing a component of the system to look at. Thanks again.
I would bet the problem is with a device called a Leak Detection Pump. These devices are a known problem and will cause this error. I had the same error some time ago and found that this device had a bad seal in it. Luckily it is easy and inexpensive to replace. Here is what it looks like for a JK -

See Link:
https://www.quadratec.com/products/evap-integrity-module-jk-jl-4861962ac?gclid=CjwKCAjwqZPrBRBnEiwAmNJsNhP2O2eWIfRwufFcZoNx7nwopfa3W2jvOXxAYAcJgwnIBTvZLZZCJBoCecQQAvD_BwE It may be the same for a XK Commander.

Dan
 

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Hmmm, that pump looks like it attaches to the charcoal canister?? I'll look into it a little more during the day today.

Not that I'd want to spend more money, but if I'm gonna change that pump out it might sense to also swap the charcoal canister at the same time??
 

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Hmmm, that pump looks like it attaches to the charcoal canister?? I'll look into it a little more during the day today.

Not that I'd want to spend more money, but if I'm gonna change that pump out it might sense to also swap the charcoal canister at the same time??
Charcoal canisters run >$200, and some include the ESIM [leak detection pump]. The pump itself I got for something like $30 and replaced without taking the canister off.

If your canister isn't leaking (I repaired a crack in mine with epoxy) I'd start with the cheaper part. It seemed to fix my issue.
 

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I would bet the problem is with a device called a Leak Detection Pump. These devices are a known problem and will cause this error. I had the same error some time ago and found that this device had a bad seal in it. Luckily it is easy and inexpensive to replace. Here is what it looks like for a JK -

See Link:
https://www.quadratec.com/products/evap-integrity-module-jk-jl-4861962ac?gclid=CjwKCAjwqZPrBRBnEiwAmNJsNhP2O2eWIfRwufFcZoNx7nwopfa3W2jvOXxAYAcJgwnIBTvZLZZCJBoCecQQAvD_BwE It may be the same for a XK Commander.

Dan
Charcoal canisters run >$200, and some include the ESIM [leak detection pump]. The pump itself I got for something like $30 and replaced without taking the canister off.

If your canister isn't leaking (I repaired a crack in mine with epoxy) I'd start with the cheaper part. It seemed to fix my issue.

Alright, today I picked up a new Leak Detection Pump / ESIM and I also got a new rubber seal / gasket for it. I'm going to try to swap it out in the next couple of days. After looking into it a bit I was seeing a couple variations of the pump. So I did crawl under the Commander to locate the pump and make sure it looked the same as the one that I got.


Does anyone have input on how the the gasket goes on?? Not sure if it goes on the charcoal canister and then the Leak Detection Pump snaps into it. Or if the gasket goes on the Leak Detection Pump first and then it attaches to the charcoal canister??


Thanks for any info. I'll post back after I get it swapped out!!
 
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