Help with P0440 Code - Leak in the Evaporative Emission (EVAP)

Cadiman1949

Nubee to Jeeps
Supporting Member
Jan 6, 2019
7
3
Albuquerque, NM
#1
Hello all, I am new to Jeep TJ's and hope there is someone out there that can help me with an issue I am having with my recently acquired 2006 Rubicon TJ.

To start off I will let you all know that I am a very experienced mechanic but have been working on Hot rods and 50's/60's Chevy's for the last 18 years... I have a lot of electrical experience so you can talk technical with me... but it's been a while since I have done much on modern cars and why I hoping to find a little help here.

Shortly after I purchased this Jeep I got a check engine light. I had taken the Jeep in for an emission test the week before and it passed with flying colors (including testing the gas cap). I checked with a scanner and got a code PO440. I did what you should always do and checked the gas capo to be sure it was installed correctly and tight (it was). I reset the code and after about 3 or 4 days the code reset itself. I replaced the gas cap and after about 3 or 4 days the code reset itself.

I checked all the visible vacuum lines and vapor hoses and see nothing obvious. The fuel tank was below 1/4 so I filled the tank and drove it for over a week on short little trips so that I could get a lot of engine starts and stops. For over 100 miles no check engine light. While on the highway with about 2/3 full tank the check engine light came on... I checked and it was a Code PO440 again. I reset the code and after 4, 5 or 6 starts the light was back on. I filled the tank again and reset the codes... no light. I filled the tank several times not allowing it to drop below 3/4 full... no light. Now that I have let the tank get just below 3/4 full the light has come back on.

Does anyone know or have an idea where I am loosing vacuum in the EVAP system or why it only seems to set a code when the tank gets below 3/4 full?

Thanks,
Rick
 

Boinked

TJ Addict
Jul 7, 2018
2,021
2,089
Mesa,az
#2
The OBD2 system will not test EVAP vacuum unless the tank is APROX 80-20% full. That is why it doesn't pop up when full.

As far as finding a vacuum leak i never have found a good way. I just start replacing lines.

Also try a MOPAR gas cap. Aftermarket ones "sometimes" have a problem sealing properly.
 

AndyG

TJ Addict
Jul 30, 2018
1,253
945
Alabama
#5
See if any accessory is on that systems fuse....I think it’s #11 but cant remember....anyway....get the manual and pull the glove box.

I wired a back up camera to mine and it threw a code. I think it is a solenoid circuit on my 03 diagram.

Also a new cap sometimes does the trick.
 
Oct 23, 2018
41
9
Houston, TX
#6
There are a few things that are easy to check for a leak for starters, there is a flexialbe piece of tubing about 10" long that is located on the drivers side next to the frame just under the drivers foot well that is part of the EVAP system that is prone to cracking. It actually connects the metal tube manifold from the purge valve to the line running along the frame to the charcoal canister in the rear of the jeep. Another place to check is the purge valve itself, remove it from the vehicle, try to blow thru it, you should not be able to blow thru it.
If those check out I would get a smoke machine, I got a cheap one from Amason for 85.00 bucks that worked great and allowed me to find a craked hose between the charcoal canister and LDP which was causing my most recent EVAP code.
 
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Cadiman1949

Cadiman1949

Nubee to Jeeps
Supporting Member
Jan 6, 2019
7
3
Albuquerque, NM
#7
This is all Great info guys! I decided to purchase a smoke machine because I can see so many uses for checking vacuum system... specially when I'm working on a 1968 to 1972 Corvette with all the vacuum systems they have. Opted for one a little nicer than an old ammo can or a paint can, the one I got looks more like an old air paint pot with a nice hook for hanging. ($120 shipped) I should have bought one by now and you all helped me just get the fence post out of my butt and get one.

Thanks!!!

Smoke Machine.jpg
 
Aug 2, 2018
90
51
Central PA
#9
I don't have this problem, but thanks for the education on the evap system located in the rear fender. I previously thought the only lines I needed to worry about were from the gas tank to the purge valve in the fender.
 
#10
I went through 3 or 4 gas caps before finally finding one that didn't throw an evap code. For whatever reason the cheap little Stent off Amazon fixed my problems entirely. Even the mopar cap I special ordered threw the code. Who knows.
 
Dec 7, 2018
70
51
South Carolina
#11
OMG my Jeep has had a small Evap leak since I have owned it. I have replaced the LDS, Gas Cap, and now the purge Valve. We will see. I will look at the hose under the drivers seat next to the frame!
 
Oct 23, 2018
41
9
Houston, TX
#12
From what you have replaced it sounds like there is a definite leak in the tubing/hoses of the EVAP system OR on the top of the fuel tank. Check out the attached post:

https://bit.ly/2TFI5iw

The cheap EVAP smoker I purchased is great, and I have used it a few times and it has always helped me find the leak(s) in other vehicles. This is a though that might help you if you do not have an EVAP smoker.
When you disconnect the hose under the drivers seat disconnect the enginer side first, blow in it toward the tank, you should be able to easly blow thru it as the LDS is open and the charcoal canister will vent to atmosphere. Now plug the vent line from the charcoal canister to the atmosphere and try to blow thru the system again. If you can blow thru it then there is a leak and you can listen for the sound of air leaking out (might help to have a second person)

NOTE: DO NOT TRY THIS WITH COMPRESSED AIR AS THE EVAP SYSTEM IS NOT DESIGNED TO HOLD MUCH PRESSURE.
 
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Cadiman1949

Cadiman1949

Nubee to Jeeps
Supporting Member
Jan 6, 2019
7
3
Albuquerque, NM
#13
I received my smoke machine today and I am armed with the factory test procedures... I'll keep you all posted as soon as I have time to run through the trouble tree, Thanks again for all the advise!
 

Chris

Administrator
Staff Member
Sep 28, 2015
33,308
20,481
Salem, Oregon
#14
I received my smoke machine today and I am armed with the factory test procedures... I'll keep you all posted as soon as I have time to run through the trouble tree, Thanks again for all the advise!
I look forward to hearing your results. Those smoke machines are in my opinion a must have tool for the DIY mechanic.

BTW, do you have a link to that smoke machine you purchased?
 
Oct 23, 2018
41
9
Houston, TX
#16
I received my smoke machine today and I am armed with the factory test procedures... I'll keep you all posted as soon as I have time to run through the trouble tree, Thanks again for all the advise!
Keep us updated, you will have to manually plug the vent as the charcoal canister, I used a wine cork in place of the filter vent, which is located where the charcoal canister is, behind the rear passenger inner fender well, in front of the tail light.