Last night was our first chilly night and saw my first CEL with codes P0456 (evap small leak) and P0300 (random misfire). Driving a 2016 JKUR with 23k.

I’ve Decided to go after P0456 first, checked the easy to check components; gas cap, and vacuum lines on the intake, no joy.

Talking to friends and doing a google search I’m suspecting EGR may be the culprit. But sticking with my logic P0456 needs to be fixed first, I’m headed to inspect the entire Evap system thoroughly, and double checking hi probability faults I can find on the internet.

there was not much material on the internet with these two codes P0456 and P0300 appearing at the same time. Stay tuned...

 

The P0300 random misfire could be tied to head gasket leaks, fuel injectors, plugs ignition, and the cam or crank sensors. Cam and crank sensors are easy to replace but should not be bad at only 23k miles. I have found the injectors are troublesome and need some injector cleaner to stop the codes or limit them. I hope you don't have anything serious like warped heads.

P0456 may be Evap system on the passenger side by the battery has some hard tubes that transition to rubber hoses that connect to the intake. Those looked like they were connected but I tugged on them when the engine was hot and cold. It was big difference when cold and loose enough to allow a change in pressure or vacuum. I tightened them up and voila it was gone.

 

If the previous post is not the fix, check your gas tank from ground at the back. Look up to the right.
One or more of the outlets on the white roll-over valve above the tank may have slightly cracked and causing the small vapor leak.
I'd imagine cold weather may cause the plastic to be even more brittle and one of the black tubes going to the tank is under tension at some mount point.
The constant offset pulling tension was my case. There are lots of good and easy JB Weld related fixes posted on this forum.