One problem related to warning light on has been reported for the 2007 Toyota Prius. The most recently reported issues are listed below.
Multiple times my 2007 Toyota Prius airbag system has failed due to a passenger weighing over 250 pounds sitting in the passenger seat. The problem seems to happen when the passenger wiggles when getting in or having a wallet in his back pocket. After he gets in the red airbag warning light comes on and it is my understanding that the airbag is then disabled. The airbag light will remain on until the dealer services the car. The dealer?s hand diagnostic tool once reported that the code was accident detected, but I challenged this and it was discovered that the code actually means occupant classification system fail. Unhooking the 12v battery will clear the system and supposedly make the airbag work properly again. The problem will reoccur when the same passenger gets in the passenger seat.