Evap code that won't go away.

Hello guys, first time poster and first time GMC owner. I bought a used 2000 Yukon and it ran fine with no issues for about a week until I went to go make my first fill up. I noticed that the gas cap was just kind of sitting on the neck and didnt think anything of it until I went to go put it back on and couldn't get it to catch and screw on no matter what I tried. No big deal, just set it back on there and get a new one. As expected I immediately got the check engine light coming on from it. Went to Napa and bought the gas cap that they said was for my truck, seems to fit on there nice and snug. Since then, I cannot get that evap code to stay gone. It comes and goes all the time. Sometimes for days, sometimes for weeks at a time. Is it possible that this napa gas cap is crap and doesn't seal right? The last time I had it into the shop to be looked at, they said my fuel strategy was off and they reset it and the codes. Sure enough though, about 24 hours later it came right back on. It doesn't seem to impact the vehicle much and since it was used, who knows if it did this before and that first week it just behaved. Kind of coincidental though.

Ive read about this issue on some other gm vehicles. From what i read you may be correct on thr napa cap. Others had to go back to the dealership to get a replacement cap for it to go away.

Mine did the same thing, come and go, come and go to finally it stayed on. I changed my cap twice however I ended up just having to change my evap solenoid super easy cheap and not time consuming at all. Ordered the part through autozone, crawled my happy ass underneath popped the old one off new one on. For me the code stayed on for about 3 trips until finally it went away for good. My buddy who is a mechanic said unless you force the codes to be erased sometimes the algorithm needs to identify the new part and its readings. 97% sure that's your problem.

It could be the vapor canister vent valve (in the back) or the vent purge valve (on intake manifold). I had the codes and message that my gas cap was loose (tighten gas cap). I replaced the vent valve and erased the codes (via code reader) things seemed good then it came up again. A new proper GM gas cap gave peace of mind but no help. Honestly I was building a smoke tester when I caught wind of the purge valve (which I had checked as good before) may be the issue so I checked it again and it wasn't seating. I replaced it and no problems since. That has been a year now. Basically it the cap, either or both of the vent valves, fuel tank sensor or a cracked or loose vent line. The system is checked between 15 and 85 percent fuel levels and proper warm up cycle.
Sometimes if I started car and it never warmed up, then came back later and started it again it never checked (or seemed to) and was clear until cooled all the way down for next cycle. Mine is a 2004 Denali.
Good Luck. Let us know.

EVAP codes can be a whole jost of issues and only one of them is a bad gas cap (or left loose gas cap). Have your codes read and report back with the proper P044X code(s).

I had one before, changed a few things and nothing. The check engine light stayed on. 6 months later it came off its self lol

Buy an oem gas cap first to see if the issue goes away. If it doesn't then you know it's not the gas cap.


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DUH DUH DUH the dreaded evap code
i spent many hours trying to get rid of it finally i got fed up and replaced all the parts for the evap system it was only about 200 bucks and evap code no more

first... yes replace the crapa (napa) cap with OEM. then get the P04xx codes and post them here. so we can know exactly what you are working with.

i dont know man in hind sight thinken about how many hours i fought with that evap system i think its way more efficient and cost effective to just replace all the parts thats after you rule out the gas cap isnt it
so in this case ive found the scorched earth approach very effective