P1455, 2005 that has been sitting for 3 years

Hello All. While my son has been out of the country for 3 years his 2005 Prius has been sitting idle with me. I would run it around the yard at least once every 6 months. The gas tank is still half full with the original gas. In preparation for him taking it back I just got it back on the road. The car runs perfectly but after about 10 miles it gave me the P1455. I have searched the forums and found a little information. I am assuming that the code has been triggered by something associated with the car sitting idle so long. Does anyone have any suggestions about where I should start looking. I hate to begin with pulling the gas tank.
It has a new 12V battery and I serviced the HV battery with the Prolong system.
Thank you.

 

Thanks. I like that suggestion.
I'm just wondering if its possible to get the gas out of the tank without all the driving. I'm doing searches for siphoning but that seems to be out of the question.

 

For anyone else with the same issue this is the outcome.
I added a bottle of Techron and drove the car until the gas gauge reached 1 bar. I filled up with Regular and added another bottle of Techron. After about 130 miles I (accidentally) disconnected the 12V battery. The code cleared and after another 150 miles, multiple days and multiple driving cycles the code has not returned. My reading of this whole experience is that fumes accumulated between the fuel bladder and tank during those 3 years of sitting (triggering P1455) and they were slowly vented after the car was back on the road.