Check Gas Cap Warning -
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post #1 of 7 Old 10-18-2009, 08:01 PM Thread Starter
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Check Gas Cap Warning

I have had this damn check gas cap light haughting me for awhile now. I have bought two different caps and hasn't solved the problem yet. I have reset the computer and got rid of it for a couple days but it is back. I am thinking aftermarket gas caps suck.....I am going to try to hit the junk yard and find an original. Does anyone know how to turn this warning off for good?

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post #2 of 7 Old 10-18-2009, 08:31 PM
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Be aware that the system monitoring the evaporative emissions system (which includes the gas cap, the charcoal canister, purge valve, etc) is "guessing" it's a gas cap based on the volume of the leak. It's entirely possible you could have a leaky hose somewhere in the system that is leaking at the same rate as a typical gas cap leak. Best place to look is at the ends of the hoses where they attach to the charcoal canister or other parts of the system - it's pretty common to find hairline cracks at the hose ends.

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post #3 of 7 Old 10-18-2009, 08:41 PM
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I have gotten the warning once, but it was on a day were there was a a big drop on the tempeture, I have never seen it again...
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post #4 of 7 Old 10-18-2009, 09:07 PM
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When you put your filler cap back, how tight do you do it?

My wife's 2005 Verona Owner's Manual sez to "click" it 3-5 times to make sure it's tight (we click it once. I don't like to overdo it, and there are people I hear at the filling station who crank the thing down. Once it clicks, it's tight enough. You don't want to break the ratchet - I usually charge $20 to remove it after that.)

Even a new cap won't seal if it's not tight enough. And, your rig probably isn't old enough to have a problem with the EVAP hoses.

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post #5 of 7 Old 10-19-2009, 05:07 PM
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Mine was on when I bought it. It turned out to be a disconnected vacuum hose under the Hemi shroud under the hood. The guy who fixed that hose left another one off when he was done. I wanted to see for myself so I took a peek and saw it from the drivers side when I looked under. I took the plastic off and replaced the hose and all was well. If yours is a Hemi, be careful when you take off the plastic cover because it pulls and touches a lot of stuff under there.

05 Grand Cherokee Limited 5.7 Hemi 265/65/17 Revos, K&N
Previous Jeeps:
1998 ZJ Special Edition 2wd- Traded
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post #6 of 7 Old 03-30-2015, 03:17 PM
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I just replaced gas cap with OEM. Noticed that my vapor canister was damaged. just installed another. connected hoses, however I have a question. Hose going to check valve didn't have a clamp. I am still getting damn check gas cap warning on dash! Should I clamp big hose to check valve? Also, hose that snaps to lower connector doesn't seem to be very is snapped into place. I am just wondering if I should clamp both?

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post #7 of 7 Old 03-29-2016, 07:03 PM
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I'm having a similar problem with my 06' WK, 4.7 L. It has been throwing a P0442 code for a while. This code seems to come and go over the last year. Recently it also started saying check gas cap. I replaced the gas cap with a OEM one and it still came back on about 4 days later. I understand this can mean it's likely detecting a large leak, so large it thinks the gas cap is off.

I made a home made smoke machine and smoked the system several times last weekend and the only place I saw the slightest smoke was coming out the top of the filter up near the fuel fill tube behind the left rear bumper.

Should this filter housing be leaking? I removed the rear bumper and still and not sure how to drop that filter out of there.

Anyone have similar problems or suggestions for solutions? Thanks.


06' 65th Aniv. WK 4.7L QTII, Rough Country 2", Treadwright Warden A/T 265/70R17
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