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Discussion Starter #1
Hi---our 2004 G500 gas cap warning went off a couple weeks ago and then lit the check engine light. I read with the code reader and it said Evap leak (large).

i made sure the cap was tight a couple times in the last week and it has come back on after i have erased the code. Again, first the Red screen "Gas Cap" then it sets off the CEL. I have also waited a couple days for it to reset itself after a few driving cycles.

Any quick fixes? I have read it could be bad gas cap, charcoal canister or a relief valve? Has anyone had luck with this issue?

tx!!!
 

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First step would be to get a new gas cap seal/gasket.
 

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I had this and was told by MB could be a sensor related to emissions as well but they could not replicate the problem. It happened twice in one day and has not happened since so dunno what to make of it; don't want to sink 200 bucks into a part and an hour labor for no perceivable benefit.

Ensure you are applying even pressure to a level fit when you replace the cap? Otherwise yea, I like Dutch's idea of trying what is hopefully a 5 dollar seal replacement.
 

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get your truck hooked up to the dealer's Star System computer - it will give you the correct source of trouble (the gas cap warning comes on for 5 other causes of evap problems). I had this happen a few years back and it turned out to be an evap canister inside the fender well, close to the gas cap.
 

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Discussion Starter #5
Thanks for the ideas!....i bought a new gas cap today at dealer to see if that is a nice easy fix...32 dollars for an 'official mercedes' gas cap...yup. Will update...an irratating item for an otherwise really trouble free vehicle---except for window regs and locks.
 
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