On our 2007 Aspen we currently have the "gascap" message and two codes which get triggered, P0456 and P0457 (loose gas cap and small EVAP leak) as well as the MIL.

The following is troubleshooting I have done so far within the last twelve months or so...
1. Initially check the gas cap o-ring to make sure it was in good condition.
2. I replaced the gas cap.
3. I replaced the gas cap a second time, just in case the first replacement was a dud.
4. Cleared the codes/DTC's, yet the "gascap" message is always there, and the codes come back within a day or so.
5. I had the EVAP system check for leaks with a smoke machine. No leaks were detected.


My next move is to replace the canister and the purge valve. If that doesn't fix the issue then I have no idea what it could be...

So then here are my questions to any one who can help...
1. Has anyone had this problem before and if so, what was the culprit?
2. Is there something else I should be looking at?
3. Did I miss to check something?
4. I also am experiencing the fuel burp issue, and from what people have posted it seems that a check valve inside the fuel tank is stuck open, could this cause the vehicle to fail the EVAP self test thus triggering the codes?

Thanks fellas/ladies/whomever in advance...

 

No.

Replacing the gascap will not help you. 457 denotes LOOSE FUEL CAP..

Every time you shut off your truck, your PCM takes a "SNAPSHOT" of Fuel level. Then you put gas in the tank.....When you start the vehicle, the before and after snapshots are compared, and the vehicle "KNOWS" he got gas. If the "LARGE LEAK MONITOR" fails Immediately after an Increase in fuel level... The PCM has no other conclusion than "YOU LEFT THE CAP LOOSE". A "Leaking cap will NOT fail a "LARGE Monitor test", but one that is left Loose, or not reinstalled, will only set the 457 code AFTER a change in fuel LEVEL.

Who did the smoke test???? It takes Practice and experience to do this....It is MUCH MORE involved than just "LOOKING FOR SMOKE".....

Now....If.....and ONLY IF...all other factors have been eliminated, The ESIM will need to be replaced for a faulty switch......This would be the little white box on the side of the canister.....If you have Never changed one..I would sugggest taking it in and having a Pro do it. They are very fragile, and in some cases require fuel tank removal for access.

 

Djinn-n-tonic,

I had a local auto repair facility perform the EVAP smoke test. It was my first time going there so I couldn't say for sure how experienced they were. What I can tell you is that it was not a comprehensive test, they were done in about 5-10 minutes and said that they cleared the codes and to come back if the codes came back on. They did say that I may need to replace the filler neck due to it possilbly being a culprit...

Thanks

 

Ok , you should find a new Mechanic.......

Re-read my explanation of How the system works, and then we are going to play with a LOGIC PUZZLE.

A culprit for the "SPITBACK" problem, yes, absolutely possible. But for the gas cap Lamp.....Not a chance...

457 is basically a Large leak, that was Noted IMMEDIATELY AFTER FILL UP. Since it doesnt go away, it indicates the problem Still exists. The cap is Tight, Because You replaced it. The cap seals the filler neck, and You had a smoke test done and No smoke was visible at the filler neck.....

Process of elimination...It CANT be a filler neck issue.

Now...If No smoke escapes, and the vehicle consistently sets a 457, and GASCAP lamp.......I would aim at the ESIM that I mentioned in my last post.
The ESIM has a pressure switch inside of it. Now if you have a LARGE LEAK, the pressure switch doesnt close, and your computer uses that "SWITCH STATE" to monitor the leak. If there is no leak, but the switch stuck open, it will do...EXACTLY THE SAME THING. Your computer doesnt know about the leak, he only knows that the switch didnt close....Its your job to find out why the switch didnt close....
If it passed the smoke test, you can reasonably rule out a leak, which leaves you with ESIM, The wiring To the ESIM, or The Computer which is unable to process the signal from ESIM.

Just for reference....ESIM....Evaporative system Integrity Monitor

 

just a quick follow up for anyone that is looking for answers...
I replaced the ESIM, just as Djinn-N-Tonic suggested (thanks!).
Actually I couldn't buy just the ESIM since it is mounted on the vapor canister.
I purchased a new vapor canister and replaced it and a week later, still no check engine light nor GASCAP message.
FYI, you will have to drop the gas tank to replace the vapor canister because of the mounting tabs, make sure you don't have a full tank of gas as I did.

 

I recently got the p0456 message but I did not recieve the "gas cap" message. If it passes the smoke test could it be a faulty sensor or the vapor canistor?

 

I just reread my post and realized how simple it sounds. Could there be anything else that would cause this issue? I am also wondering what to expect to pay for the smoke test? I understand it will vary by location, but what would be an average.

 

I have the same problem, if you notice when you remove the gas cap, the metal flap is missing,,,, that little flap is the culprit.
You will have to replace the entire fuel filler neck in order to solve the problem.

 

Two or three years ago when the TSB finally came out for the filler neck, I took in the Aspen and got it repaired, that fixed the burping issue. As far as the check engine light and evap codes, i had to replace the vapor canister as the culprit was the ESIM....

Thanks for your input!

 

If you are getting a P0456 and/or "Gas Cap" light, replace the ESIM. You do not have to replace the canister. You can get the ESIM by itself now. I had the same issue and just replaced the ESIM. A simple 5 minute job. Problem solved.