I’m getting a check engine periodically, it’s P0449. This is a “Evap Vent Code”. Is it being caused by the Gas Cap or the evap vent solenoid? Both are original. By the way the vehicle is a 2007 Yukon Denali.
The cap is easy and cheap to replace, so try try that. There is a valve under hood that can also cause this. Also cheap and easy to replace.
And then there is a sensor in the top of the gas tank. THAT is a bear to get to unless you can cut a hole under the rear seat and access it that way. Works on Suburbans and Avalanches, maybe Yukons, too. Google “Yukon evap sensor” The sensor is also cheap to buy.
Try YouTube as well for a few diagnostic tips
P0449 is not a leak code, so replacing the filler cap would be a waste of your money, in my opinion
This code often occurs because the evap vent valve is plugged with dirt, spider webs, etc.
I seem to remember your Yukon is 2007 model year, correct?
If so, this bulletin applies to your vehicle
Mind you, I’m not there with you and your truck, and what’s described in the bulletin might not actually be the cause of your problem.
But we have lots of Tahoes and Yukons of your vintage in our fleet, and this modification WAS necessary on many of them. These guys do drive off road and get there evap system all full of crud. I’m not sure what kind of driving situation you have, though.
Replaced the gas cap and that didn’t work. So I think my “next step” is to replace the sensor. I think i’ll wait for warmer weather before i tackle that 
Just out of curiosity . . . you made no mention of that bulletin I provided to you
Did you read it?
Do you feel it’s not your problem?
I don’t mean to sound like a jerk . . . but I told you a few weeks ago the code you had wasn’t a leak code. And I also said replacing the filler cap would be a waste of your money.
As for the fuel tank pressure sensor, in my opinion, that will be a lot of work which will likely not take care of the problem. The sensor isn’t terribly expensive, for what it’s worth.
You’re not being a jerk. I did read it. I’m not having issues filling the tank. All I have is the CEL comes on. I replaced the filler cap because the one I had was the original one, it was cheap and easy. I have saved you link and will look at it more closely.
I used this link as well. https://www.autocodes.com/p0449_2007_gmc_yukon.html
I didn’t assume you had issues filling the tank
That said, I’ve fixed several Yukons in our fleet with that exact same code, as per the bulletin, and they also had no issues filling the tank
I looked at that link you posted . . . thank you
In my opinion, they’re giving you bad advice by including the fuel cap as a possible culprit
A shop might be able to read what that sensor is telling the ecm using their shop scan tool. Or they might be able to tell by just measuring the voltage or resistance coming from the sensor. A proper diagnosis might prevent an unnecessary parts replacement. Parts replacements always come with the risk of damaging something else in the process, or the replacement part is faulty and once installed it fails a month or two later. Not a problem you want.
I haven’t read through the other responses or links but whoever advised you to try a gas cap for that fault code doesn’t understand how the evap system works. You have either a fault in the venting system or a failed evap pressure sensor. It’s not likely a DIY’er can accurately diagnose this, the easiest part to try would be the vent solenoid.
Since my truck is getting close to State inspection time I thought I would address this P0449 error. I found this link on the web https://www.autocodes.com/p0449_2007_gmc_yukon.html and replaced the Evaporative Emission Vent Valve Solenoid. If you have access to a lift this is a Very easy job. Needless to say, it worked. No more Check Engine Indicator.
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Thanks for the follow-up OP, good for you. @db4690 s advice was spot on, so thanks to them also.