One problem related to brake disc caliper has been reported for the 2012 Toyota Prius. The most recently reported issues are listed below.
My 2012 Toyota Prius v (mileage: 55155) has had a failure of the rear brake pads and rotors due to excessive rusting. Please note the front brakes are in great shape and show very little wear. The service manager was quick to point out that he was only a franchise store and was not responsible for the design of the rear brakes. He stated that this happens occasionally on the hybrid cars they service and if the manufacturer had coated the brake (I believe he was referring to the slide area of the caliper where the brake pads rides) that the brake pad would not have hung up and worn out along with destroying the rotors. I am a former licensed aircraft mechanic and a licensed engineer with the state of illinois. Clearly there is no reason for the rear brakes to fail before the front brakes and certainly not the rotors. This car has been serviced by the dealer every 5000 miles, which demonstrates the failure was not due to neglect. This failure mechanism needs to be addressed before it causes an accident.