If you intend to test and repair this yourself you will need to familiarize yourself with how and why evap systems work to start. Then you'll need some tools to test with, a good DVOM and a smoke machine are essential. Then you'll likely want a scanner that has bi-directional controls so you can activate and deactivate particular switches/circuits in the system as the diagnostic strategy demands. These tools should run you about $5000.00 at the low end before you by your manuals. It may be cheaper to bring to a certified technician to have the system tested, may run between $45-$85 for diagnosis.
To address your codes, the vent solenoid is likely stuck closed or that part of the system is clogged/plugged somehow, solving this would likely eliminate both codes.
The vent solenoid if shut will cause no venting and pressure buildup while your trying to fill your car. The pressure is what shuts the gas nozzle off. When the car is on and the ecm asks your pressure sensor what the pressure is. there has been no vent because the valve is "shut" so the pressure is higher than it should be. The sensor simply responds to the ecm that the pressure is too high, the ecm decides that something is wrong here and sets the code.
This is another great example of how codes do not tell you to replace parts. They are there to tell you what systems or parts of systems the ecm has found a fault with. The likelihood of both of the pressure sensor and the vent solenoid failing at the same time is so rare you'd have a better chance of winning the lottery.
In some cases the vent valve's breather gets clogged with dried mud, the fix is to clean out the mud and make it so mud can't do that again. That may take only 5-10 minutes, but it may take an hour to test the system to find the problem.
Good luck
