I got the new cap in the mail yesterday, installed it and have driven it about 30 miles so far today and the error is still showing up.

Next stop taking it to my mechanic.

 

probably not the case for you but something to check, look at all your evap lines next to the fuel tank back to the module above the spare tire. had a 5th wheel hitch installed and the nimrod putting it in drilled through one of my lines. came up at first as a check gas cap code. critters may have gotten up under yours and tried to re arrange some lines for you

 

Yep, time for a smoke test. Make sure the mechanic is properly equipped. It will quickly show where any leak is at, whether it be in the various plumbing lines, purge or vent valves, gas cap seal or wherever. Make sure that he also checks that the purge valve is opening when the computer commands it.

 

 

Before taking it to the shop...

Unless you have an imminent emissions test, I'd be inclined to just reset the PCM and start from scratch to verify the concern is still present That way, there's no chance of old or stale data causing any issue.

 

I just went to my mechanic and he reset it for free and used a steel wool thing to get a small amount of rust off the metal lip of the wide opening. He said to come back if the light comes back on.

I will check the lines underneath the vehicle next. Another mechanic at the shop recommended a smoke test so that's a next step as well.

Will the light come back if there is still a problem? Or is this potentially a way of just sweeping the problem under the rug?

 

Yes.

No. The mechanic did well. He did one thing (only!) that was a potential reason for your symptoms, reset the system and told you to come back if the issue returns. A very prudent set of steps and, that, in my book, makes that mechanic highly recommendable.

 

I had that issue when I would keep filling the tank after the automatic shut off at the pumps (you know how you squeeze every last drop into that tank)- I sucks it up and takes forever to clear- once I started letting the pump shut off itself - the code cleared after a couple days and I haven't had it since.

 

The fix for this turned out to be a bad solonoid. There is a good description of what this part is and some other details here:
https://www.yourmechanic.com/estimat...id-replacement

It's about a $60 part on autozone for a motorcraft.