How to know if the evap solenoid or the evap canister needs replacing?

Great question. There are no real tests or maintenance that needs to be performed.

The way you will know there is an issue is you will have stumbling or issues in performance only after you fill the fuel tank. Or the engine seems to run rich so you will find fouled spark plugs.

The canister will have raw fuel in it but you need to remove it and shake it to find that out. You can also remove the solenoid and inspect it for what looks like soot or residue inside of it. This is actually the charcoal that has broken down due to it sitting in raw fuel inside the canister.

Basically you will see different performance issues when the purge is supposed to be closed. It sticks open and due to it staying open when the PCM expects it to be closed, the engine runs rich.

The fuel pump shutting off could be a vent line or the canister is full of fuel and causing the fumes to back up the line and shut the pump off.

However, if you have this and no performance issues then I suspect you have a filler neck issues or even just the vent line is plugged. You could have a leaf or something in the filler neck that is causing it to back up as well.

I attached the info below on both these items so please run through this and let us know what questions you have.

Thanks

What is the filler neck and what am I looking for?
Also, where is the vent line and what am I looking for? Will this issue give a "check engine soon" icon? Will it pass emissions? And, what is the code for this problem?

The filler neck is the place you put the gas nozzle and that is the tube that leads down to the fuel tank.

The vents lines are on this as well that run right next to the filler neck.

If they are clogged then there will be a restriction in the neck and the fuel will back up and shut the pump off.

Do you have a check engine light on? This would not cause a light but we should check the codes if the light is on.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Below is the process for the neck. This will give you some pictures of what I am talking about. This will not fail most emissions as they do not test the ability to put fuel in the vehicle just how the engine operates and the emissions that come out of the engine.

However, if the light is on then that will most likely fail emissions as they don't want any check engine light on during the test.

What's the "fuel pressure relief" procedure?

Sorry. I normally include that. Please see the process below but basically you just connect the gauge with a shop towel around it so any fuel spray will be caught. It is nothing fancy.

Detail is below. Thanks