I have a 2005 Prius and have never had any problem with it. But i had an unusual situation recently and wonder if anyone can explain what happened. I was parked on a very steep driveway, facing downhill. When I tried to back out, backing uphill, I had to have my left foot on the brake as I stepped down on the accelerator. But nothing happened. Only the battery motor was on and it was not strong enough to keep me from rolling forward into the garage door if I hadn't kept my foot on the brake. Finally, after pumping it several times, the gas motor kicked in & I could back up. Any suggestions?

Reverse ONLY uses the electric motor. Because of the rotation of the planetary gear, it is not possible to power a Prius in reverse with the gasoline engine (ICE). Apparently the battery was almost drained when you parked it. The ICE then generated enough juice for the elec motor to then power the car out of the drive:)