It’s usually a single specific code, but from the drive-by search I did, any of those can also be due to the cap’s seal, considering the TSB also deals with the filler tube not sealing. Likely not, but after a decent inspection that nothing jumps out at you from, seems good to rule out [to me] as it’s cheap enough.
Assuming a valve or canister issue that isn’t obvious, I’d agree with you(not really DIY friendly), but a decent percentage of these can be pretty obvious assuming you run your hand along them/give a good visual inspection, checking for rust, cracks, etc..