Evaporative System?

Hello, how are they failing you for inspection if no codes are present? Your check engine light is not on, correct? What are they detecting is causing a failure? Is there any other information on the paperwork they gave you, because that sounds very strange. I live in NC as well. And without a check engine light on and no codes stored, I'm not sure how they can fail you. They are not measuring emissions at the tail pipe, correct?
A bad Vent valve stuck or sticking partially closed will make it difficult to fill the tank, so I would check that first, Ill post some info on its location. But I would definitely think there would be a code for that when the Evap runs its self-test. If you have a scan tool, can you look and see if all your IM monitors have been run.

This is the filler neck for the gas tank and the venting tube that runs down to the Vent Valve, it should be open to atmosphere when the vehicle is off. This way when you're filling your tank the vapor can escape up near the filler cap and allow fuel to enter the tank without creating a pressure difference and shutting off the stations handle at the pump.
It's possible that the IM Readiness for the Evap system has not passed and that's what they are seeing. And it just has no set a code yet, or the scan tool being used is a basic OBD2 global scan tool not seeing the code, but the Check engine light would be on in that case, so I suspect the Evap self-test has not passed yet.
I've added some information on getting the IM Readiness monitors to run and are completed.
But I suspect the Vent valve is sticking closed, so if you find the Vent valve has an issue, after you replace it, follow the conditions that need to be met so the monitors will run. Such as 15 to 85% fuel tank level, certain temperatures and the correct amount of time between drive cycles. Some scan tools can run Evap tests as a special function.

The IM Readiness monitors are emissions related. In your case the Evap system was not able to run its self-test or ran the self-test on the Evap system and failed the test. When the ECM (engine computer) in your vehicle runs its Evap test, (and it's a little different from make to make), but it will close the Vent Valve, this seals the gas tank area from atmosphere. It will leave the Purge valve open so that the gas tank can be drawn into a vacuum from the intake manifold while the vehicle is running. It will next close the Purge valve and monitor the Fuel Tank pressure sensor to see if the vacuum in the tank is held or if a leak causes the vacuum to be lost and the tank approaches atmospheric pressure that test will fail. The Tank pressure sensor is extremely sensitive, there are a number of steps when it runs this test. So, the next test it will run is when the vehicle is off, the ECM will close the Vent valve, close the Purge valve and monitor the amount of positive pressure rise from the tank. When the vehicle is shut off, everything is still warm and there is a positive pressure rise in the tank and the Tank pressure sensor monitors this for a specific amount of time. It runs tests like this to determine if there is a leak in the system and the size of the leak.

It runs vacuum decay tests and positive pressure tests because there are differences. When the system is under a vacuum, hoses and connections are pulled in, and the opposite happens with positive pressure. You are correct a code should set if a leak is found, but for your vehicle the vacuum decay test must fail 2 consecutive tests to set a P0445. This is a Large Leak code, if a small leak is detected a P0442 will be set.
The system also runs some other tests to specifically test the Purge solenoid and Vent valve.
I will post all the test info, so you have each one and what the ECM does for each test. It might be that the Vent valve, or some other location is intermittently leaking. And it hasn't reached a point where it can set a code, if it fails one test, then passes another, and it's not 2 tests in a row, that might be why it's not throwing a code yet.
But some Evap tests can take a bunch of drive cycles with a certain amount of hours in between each drive cycle and key Off cycles to complete. Your vehicle looks to take 6 drive cycles with 17 hours in between drive cycles to complete. It can be frustrating considering you're trying to get through inspection.

You mention a Catalyst failed IM Readiness as well?

The first two pages below are the Evap Tests that are run, pages 3-5 are what to do if any IM Readiness monitors read "No" instead of "Ok or Pass".
But with the issue of filling at the gas station is a clue, the gas station handles are designed to shut off when there is fuel vapor coming up to the tank filler neck. So it might be that the Vent valve is stuck part open and that's why you can get a couple gallons in before it shuts off. Usually when the vent valve is stuck completely closed you can't get any gas to go in, it will constantly click off, or it will cause the gas to come flooding back out of the filler next and make a mess all over.

Here is a guide we have on filling the tank issues as well:

The Catalyst Monitor can be two different types, Catalyst Efficiency and Heated Catalyst Monitoring

https://www.2carpros.com/articles/comprehensive-guide-why-your-cars-gas-tank-wont-fill-up-and-how

You might not notice any issues, and if you look through the info on the Readiness monitors, it might be that the vehicle has not had a chance to sit for a 17 hour period with that certain amount of gas in it, for 6 drive cycles yet, If you look at the pages above, 3 and 4 it shows all the conditions that need to be met for it to count it as 1 complete drive cycle. Also, with vehicles that sit a long time, that's where I have seen rodent damage the most, I'm not sure if that's an issue where you are. But the vehicle also lost the Keep Alive memory if it was sitting with a dead battery for that long. So, the ECM is still relearning or has been relearning its fuel strategies since the new battery was put in it. There's a bunch of small variables here. But start with the Vent valve and go from there. I recently had a customer who was able to buy a yearlong temporary tag so he could extend the time until the vehicle had to be repaired. I had never heard about that before, but it was here in NC. I just repaired his 07 Nissan last week, so he can get through inspection now, I can ask him about that tag if its something you would need to do.

If you read through the sections of the pages 3-5 that I posted up top, thats what it can take for the Evap system to complete its IM Readiness for this vehicle, Its a little different for each make. But everything in the info is straight from service info, They may put it in those terms because the vehicle may not reach each of those conditions all at once. It depends on a persons driving habits. Pages 1 and 2 describe all the tests that the Evap system runs to verify there are no leaks anywhere. It runs each specific test to check a certain part of the system, Purge, Vent valves, gas cap, charcoal canister, hoses etc. Read through it, I only marked in orange and green arrows the certain criteria needing to be met, On most scan tools, even some basic Global OBD2 ones there will be an option to check the condition of each system. I/M is Inspection and Maintenance. Bellow is what is required by law for the OBD2 system to have in check for emissions standards. Most of the time if the vehicle is running ok you wont even know the vehicle has already gone through all its self tests and is good to go.
The fact that the check engine light has not set a code means, either it has not be driven enough consecutive cycles with a fault to set a code, or the issue is intermittent, or the last but unlikely possibility is the Keep Alive memory power feed is not sending 12votls to the ECM. So the memory is basically being reset every time the vehicle is turned off. But you only failed 2 of the monitors, Catalyst and Evap. Theres a list on the sheet below of the monitors.
As for swapping parts I would have to look up the part numbers for the year make and model of the ones you want to pull parts out of.
I would just check to see if the vent valve is operational. If you apply 12volts to it, it should close and not allow any air through it. Heres the Vent valve connector so you know which wire is power. Is ground side controlled, so hook 12v to the Red/White wire and give it a ground real quick and see if it closes. Inspect the harness while youre down there. It should have power on the same wire with the key On.

Okay, when checking that Vent Valve, make sure the hose running from the valve up the filler neck is clear, not bent or damaged in any way. That needs to allow vapor to escape so fuel can enter the tank without any pressure difference. Yeah, please let us know what you find, and take some pictures if possible, as well. It will help future customers if they run into this issue on the same model. Thanks

Sure. Here's the entire Canister removal (diagrams 1, 2). The Purge valve (diagrams 3-6) I also put the Purge valve connector in there so you can find it by wire colors if needed. I'm not sure why their diagrams look like its pointing to a front oxygen sensor, but you'll find it. The 7th diagram is a view from the top of the tank, and the fuel tank pressure sensor.

You need to only lower the side of the tank enough to get to the Vent Solenoid. You don't need to remove the tank to check it.
But here are the diagrams for dropping the tank if you need to. To lower the right side of the tank if you can't get to the Vent solenoid, you'll need to lower the tank strap on that side. It will be very difficult to remove the tank without the vehicle being on a lift.
What code was it that the shop was able to pull from the ECM? I was just looking back over your posts, it's odd that it failed more monitors now, those should have been fine. I think we should check for a power loss at the computer. With the pressure at the gas cap, or probably vacuum, you still need to check the Vent solenoid, but go through the fuses with a test light and make sure none are blown and ill pull up the ECM diagram so you can check the KAM, keep alive memory power feed. But was the code for the vent solenoid?

I've added the ECM C1 connector and pin 20 (Red/White wire) is hot all the time, its the memory B+ feed.
The Catalyst monitor won't be able to pass if the Oxygen sensors are not passing either, also if the Oxygen sensor heaters are not working the sensors won't work and it won't pass for that reason as well.

Thats strange, I'd be interested in seeing what the engine computer's live data is reading for a couple of reasons. Such as the Long Term and Short-Term Fuel Trims (LTFT and STFT) they should be less than 10% either positive or negative. If you have a scan tool that can look at some data while the engine is running. The Catalyst is the more concerning monitor, just because it involves the Oxygen sensors and Catalytic converters are just plain expensive.
If you could look at what the Oxygen sensor voltages are doing as well, that would help figure out why the Catalyst monitor is not passing.
And another thing you would be able to watch is the Fuel Tank pressure sensor, the pressure in the tank would start to rise after a good long drive if the Vent solenoid is sticking closed. It doesn't rise a lot, but because the pressure sensor is so sensitive you would be able to see the pressure rise.
I did come across a TSB on premature Catalytic converter failure due to these coil engine block Grounds breaking, so inspect any grounds on the engine block for this type of wire strain breaking. This must cause a weak enough spark that the engine runs rich but doesn't set any codes for it.

Does this scan tool allow you to select the year make and model of the vehicle? I'm just going through the user manual for it, I'm not sure I understand what it's even displaying there. Under the main menu can you select Global OBD2? And do you happen to be around Rowan county in NC? On the Innova website it looks like there might be updated software for scan tools, you could attempt to update it.

https://www.innova.com/pages/download