I have a recurrent problem that is triggering a check engine light. It has been in the shop multiple times and they can't find the problem. However, I think I have finally detected a pattern, and want to know if you can tell me what it means.The error code is the same code that you get if you leave the fuel cap off, an evaporative emissions code. I don't remember right now exactly which one.However, if I clear the code, it will not trigger again if I keep the fuel tank above 1/4 full. It is only when the tank is 1/4 full or less that the code gets thrown.If you need the actual code, it will take me several days to drive the fuel level down to where the code is thrown again.Thanks for any input.

I've had a car throw a code when I didn't have the fuel cap screwed on tightly enough. Is there any chance it's a faulty cap? Might be a cheap try just to put on a new cap and see if that fixes it.

I had to replace the hoses on our Durango years ago that run from the gas tank to the EVAP canister if I'm remembering the term right. It was throwing the loose gas cap code. The short section of hose was very brittle and falling apart while other rubber hoses were like new.

Take it to a shop that has an evap smoke machine. Make sure it has less than a 1/4 tank. The shop will hook up the machine and pump smoke in the system. Eventually the smoke will exit through the leak, and become obvious where the problem lies. This is the definitive test for such issues.The likely candidates might be evap canister, filler tube, vent hose.

Not knowing what your vehicle is I would also suspect the EVAP canister and related parts.

Had the same issue with my 2010 F-150. It was some sort of EVAP solenoid that went bad that they had to replace. Took a smoke machine to find it. It was a simple swap/replace after that. Definitely wouldn't find it on my own.

Check Engine Light | Good Sam Community

Perrysburg_Dodg
Explorer
Dec 10, 2013
Not only "That would be unethical" but what if they failed in warranty, it would cost the manufacture then.

OP sorry to hear about your Mother's passing. Since you have had the cap replaced and that did not resolve the issue the next step would be the smoke route. Most likely it will be a bad evap solenoid vacuum line or the solenoid itself, then the canister.

Every spring around here they offer free gas cap testing, if your cap fails or is more then 4 years old they give you a new one FREE!

Don
Hannibal
Explorer
Dec 10, 2013
That's the one. The other hoses are like new while that one gets brittle and cracks just out of warranty. Almost like an engineered service visit, just out of warranty. But they wouldn't do that. That would be unethical. :B
_40Fan
Explorer
Dec 10, 2013
If you haven't found it by now, have your mechanic check out this hose on the evap canister.
Vulcaneer
Explorer
Dec 04, 2013
A good smoke machine can find a leak of .020 of an inch. About the diameter of a small paperclip wire. Our shop has found every leak we have encountered. Surprisingly most are rust at the top of the filler neck where the gas cap tightens. Sometimes even new cheap filler necks have a slight nick in the top. They won't pass the test. Changing the gas cap does not help that issue. Nor does it resolve the vent hoses or evap canister issue. But the smoke machine will find the leak. If you really want to fix the problem, spend the money for the smoke machine test.
mike2wheels
Explorer
Dec 02, 2013
We have an '06 Town and Country that went through intermittent check engine light for a couple of years. For months we dealt with it by tightening the fuel cap an extra turn. The dealer said they couldn't find any codes in the computer. Finally, I replaced the oxygen sensors and we didn't have another check engine light until the thermostat went bad this year.
Chuck_thehammer
Explorer
Dec 02, 2013
Dave H M wrote:
My luck never runs this way. However before I took it in I would check around the fill neck and make sure that if ist had a plastic insert or the like, it was in good order.

I had one with a chunk broken of it on my last Ford. Guess I missed the hole. :S

many Ford models have plastic filler necks.. and crack in the cold...
causing the check engine light for EVAC. NO vacuum in fuel tank system.
Me_Again
Explorer III
Dec 02, 2013
Our Buick Rainier has a vent solenoid that I had to replace. I would just fill the tank at least 50 percent, reset the code and let the new owner deal with it.

Chris
Dave_H_M
Explorer II
Dec 02, 2013
My luck never runs this way. However before I took it in I would check around the fill neck and make sure that if ist had a plastic insert or the like, it was in good order.

I had one with a chunk broken of it on my last Ford. Guess I missed the hole. :S
Chuck_thehammer
Explorer
Dec 01, 2013
I forgot to say... cracked neck of gas tank, broken clamp on neck of gas tank.

anything that will cause a small vacuum leak.. in the fuel system..
thats gas tank and filler neck, all fuel vacuum lines, connectors and rubber connector hoses. EVAC valves and control circuits.

and there are over 30 feet of vacuum lines/hoses on a mini van. and all it takes is a single PIN hole. thats why the smoke machine.
buta4
Explorer
Dec 01, 2013
1. Did you personally replace the fuel cap?

2. Always screw the cap on TIGHTLY when finished refueling.