New member issues 2005 STS

Picked up a used low mileage 2005 STS last August. Love the style, comfort, and performance. Had a couple of issues pop up that I could use some help with.
Pulled a code that shows a fuel tank pressure sensor problem. Engine light came on for a while after I topped the tank off once and stayed on for a couple weeks.
Then the light went off for an equal amount of time. When it came back on it stayed on for several of the winter months. During a warm up last week the light went
out for 3 days then came back on. I ordered a sensor but have not had the opportunity to replace it yet. Has anyone out there done this and was it difficult to do.
Part location on the web doesn't tell me much. It is located on top of the fuel tank or is it part of the emissions canister wherever that might be?
Second problem is with the drivers door lock auto unlock system. With the FOB in my pocket the drivers door will not unlock when I pull the door handle. The passenger
door will. If I use the FOB to unlock the car the door will open. The only thing I have checked so far is the drivers door module fuse under the rear carpet. It was fine.
I read some of the forum replies on lock problems but to be honest I was a bit confused. Any help on these issues would be greatly appreciated.
Jerry