Car doesn't want to start after I fill up with gas.

Where is the fuel pressure sensor located?

The sensor is part of the fuel pump assembly and is mounted on top of the tank or inside the tank. It's part of the evaporative emissions system (commonly referred to as "EVAP") and reads pressure in the fuel system to detect evaporative leaks, such as a loose or faulty gas cap.

Fuel Tank Pressure Sensor ' Cars.com

I think you should go for manual first after that it would be easy for you to solve your problem. I had visited this site past 2 months before for my vehicle and find it quite helpful may be you will also get something useful here
Buick Allure LaCrosse Workshop Service Repair Manual 2005 2006 2007 2008...

Sounds like the purge solenoid is leaking

sounds like an issue with either your carbon filter or purge solinod being blocked

The P0496 DTC code is a generic code which applies to all vehicle makes. A quick search on the 'net shows that this code seems to be more common with GM (Chevy, Pontiac, etc.) vehicles. In Acura, Honda, Hyundai, Kia, and Mazda vehicles, this code is described "EVAP system high purge flow" which is the same thing.
try use maxiscan us703 to clear the fault code.

Replace the fuel sending unit in tank.

Usually its the oxygen sensor or a problem with the Cat.

sounds like you are having an o2 sensor problem. have that particular part looked at

You need to Replace your Cas Cap. The Seal is bd on it and is allowing air into the Fuel Tank Causing Both Dash Lights. This should solve your Problem.