Let me introduce myself: I am a "new" owner of a used 2002 Prius which I bought 3 weeks ago from someone I found on Craigslist. I had the car inspected by a local shop (not the dealer as the dealership was too busy and time was critical). They said the car was OK except for the spark plugs having a bigger gap than normal and may need to be replaced soon. They did not check the hybrid battery or electric motor as they were not qualified for that. The hybrid system had just been serviced 5000 miles ago under warranty with a new battery installed so I did not think it would be an issue. Today, I drove to lunch (about 1 mile away) and after lunch the master warning light came on, along with on-screen icon saying the hybrid system had a fault (the car icon with the exclamation mark through it). Also, the check engine light on the dash came on. I was puzzled and shut off the engine and started it again. The warning came back but I had to be back at work so I decided to drive back. Everything seemed fine, the car drove normally and I did not hear any sounds or other abnormal behavior. I called the dealership and they were busy until Monday and they said if the car seems to be driving normally I can keep driving a little as necessary. When this happened, I only had one dot of gas remaining in the tank (the last dot before the low gas alarm goes off) and it was my intention to go fill up on the way home. After work, I started the car up again and the same error message/check engine light came back on. I drove 1 mile to the gas station, filled up and after filling up all warnings and lights went away. I drove home (30 miles on the freeway) and ran a few errands this evening and everything seems normal, no faults or warning lights. It seems that filling up took care of this? Should this be something I should have checked out or was this just because of the low fuel level? Thanks in advance for any advice.