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Discussion Starter #1
Ok, I have an 08 JK X model with the PO456 code showing. After clearing he code I changed the gas cap twice and the evap canister vent valve, code still pops up after clearing. What's next? Smoke test? I don't have a smoke machine!
 

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Using a smoke machine is the next step. If not you are guessing at which part may be broken. Also there are lines and electrical wiring to take into account.

One thing you can just try without a smoke machine is check to see if the purge valve flows air even with the car off. It shouldn't flow any air. You might get lucky that is the problem. You can check this with a vacuum (mityvac) or just blow through it.
 

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I had a similar issue with my old '07 Sebring. I had it in the shop 3-4 times over a few years. They would "fix" something but then the code would pop up again in a few weeks or months.

They finally traced it down to a dirty ESIM filter. Once that was replaced I never had an emissions fault code again in 4-5 more years of owning it.
 

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Discussion Starter #5
Ok, I figured out what the problem was. I ordered a new gas cap from an internet search listed for my Jeep for the year and make. The one I got looked like the original but had a different seal that I didn't notice. Seems the JK's have a different gas cap than the other cars I own so be careful when ordering a new one, match them up with the one that came with your Jeep.
 

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P0456 Update

I wanted to post an update for my P0456 small evap leak code. After replacing Evap Canister, White valve that goes to canister and gasket, and purge valve in front of engine, the light came back on after 2-3 days! All the parts were around $100 and took less than 15 minutes to install so not that upset. Tried 3 different Gas caps including Mopar.. Further research led me to looking at the line going into the gas tank. It is one of those sophisticated hoses that attaches to the nipple on the gas tank. My son's Jeep is lifted so I could easily see it by crawling underneath. There was a small crack in the tube similar to what many others had seen so it looks like it is common. Dealer wanted $700 to replace since you have to replace the whole tank. I took the advice of the YouTube poster and purchased a $6 tube of JB Weld Plastic bond and covered the crack. I also cut the 2 ties that held the cable and re-routed since you could see the stress it was putting on the nipple. See enclosed picture of the crack... Been 2 weeks no and still no code.
 

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