One problem related to brake disc caliper has been reported for the 2002 Toyota Prius. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2002 Toyota Prius based on all problems reported for the 2002 Prius.
Applied brakes while car was moving slowly, less than 10 mph, and heard loud grinding sound coming from left front as car stopped. Shifted to reverse and car barely moved, about 1 foot, which was accompanied by the loud grinding sound, then stopped. Turned car off and could find nothing interfering with the wheels but did find pieces of brake pad on the ground along the path the left front wheel had followed. The left front wheel appeared as if the calipers were holding whatever remained of the brake pad and/or backing tight against the rotor. Brake function had been normal for prior 7 11/12 years, ie, since I purchased it as a new car. There was a bothersome grinding, sometimes rattling or squealing noise from the left front wheel since the first year of ownership and I was repeatedly told by the dealer that nothing was wrong. Brake rust had gradually accumulated on the left front aluminum wheel but not on any others and the dealer blamed that on winter salt. It was towed to a different dealer and the front brake pads were replaced along with the front rotors being resurfaced. Despite my request, the brake pad from the other side was not kept nor was its thickness recorded. Nothing I told the service manager was relayed to whoever worked on the car and that person only recorded that the tow truck driver said the left front wheel was frozen fast. The car, 2002 Toyota Prius, had 43561 miles on it when this occurred and should not have had significant brake pad wear given the hybrid braking system and braking gear as well as my driving style. After the above repair was done, I learned that there was a recommendation that the left front rotor be replaced. I will have this done by a private mechanic so that the part will not be discarded.