Two problems related to engine shut off without warning have been reported for the 2009 Toyota Prius. The most recently reported issues are listed below.
The contact owns a 2009 Toyota Prius. While the vehicle was traveling at a speed of 60 mph the vehicle suddenly shut off without warning and would not restart. The vehicle was towed to the dealership who stated that the failure could not be reproduced. The failure occurred twice prior to the recent failure. The VIN was unavailable. The current and failure mileages were 20,000.
I purchased a new 2009 Toyota Prius hybrid (gas/electric) on March 31, 2009. The car worked great, but with only 490 miles on the odometer, I did a routine shut down of the car on may 20, 2009 which turned out to be anything but routine. During this event, I shut the car off using the procedure taught to me by the dealership salesman, which was the same procedure outlined in the user manual. However, at this shut down, a very dramatic power surge went through the system, jolting the engines in their motor mounts (I heard an extremely loud squeal when the engines, both gas and electric, jolted to a stop, which I assume was the motor mounts taking the force of the power surge), and moving the car violently forward stopping with the transmission lock and brake which I had set). This was a very unpleasant and un-natural event. Following this event, the car did start and operate through its functions, but the driving characteristics changed dramatically. What had been a smooth operating synergy drive system was now slightly grabby both in acceleration and deceleration, and I experienced hard clunk shifts when driving. Approximately every 15th gas engine shut down, the gas engine would diesel and have a disturbing long cycling shut down vibrating and jolting the car in an alarming fashion which is not safe. On June 2, 2009, I brought the car into my Toyota dealer service department, was told the car "can't do that" and was told the computer showed nothing wrong. On July 8, 2009, I went to another Toyota dealer service department, they said the car was rough, and tried to re-seat the engines in the mounts, which temporarily corrected the problem until a major gas engine jolting shut down occurred again. I took it in again on 24 September, 2009, and asked to have the engine mounts replaced. They tried to reseat the engines again, with no success, and the random jolting gas shutdowns on the hybrid system continue, which are a safety hazard during operation.