Two problems related to power assist brake have been reported for the 2005 Toyota Prius. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2005 Toyota Prius based on all problems reported for the 2005 Prius.
While test driving a new '05 Toyota Prius I came to the conclusion that its braking system is inadequate. Emergency braking while turning easily induces under-steer because of the regenerative braking. As the aggressive brake-assist takes over there is "snap" over-steer and front wheel lockup. For average drivers this can result in complete loss of control.
2005 Toyota Prius -- floormat becomes lodged between pedals. -- while driving at high speeds (60-70 mph) on the freeway, I noticed a loss of sensitivity on both the brake and gas pedals. I had to press very hard to get a reaction from either pedal. As a result I was unable to keep driving at the same speed as the surrounding cars. Everything else seemed to be operating normally. The sensation continued for a few minutes until I could safely pull off of the freeway. Upon investigation, I realized that the floormat had come unhooked from its restraints and stuck between the pedals and the floor. I secured the floormat to its hooks once again and continued driving without trouble. This has happened a couple times since, but I recognize the symptoms and fix it promptly. However, I fear that another owner might experience this when they need to brake or accelerate suddenly to avoid an accident. (I noticed another posting that described the same problem). Perhaps Toyota should install locking hooks rather than the current ones that easily twist and unhook from the mats.