Two problems related to brake drum wheel cylinder have been reported for the 2011 Toyota Prius. The most recently reported issues are listed below.
On uneven road surfaces (washboard road, many small potholes, gravel roads, rough road shoulders) brakes would give out if braking hard. If felt like once abs kicked in the brakes would get almost completely released. The car would brake just fine on flat surfaces, wet or dry. I have multiple vehicles and know how abs brakes work but thought the Prius brakes were just a bit more sensitive and I have to watch my distances more carefully and avoid hard stops. Then on April 23, 2018 the car started to make some strange noise but no dashboard lights came on. I continued driving and noticed the brakes were working only intermittently. After I almost crashed when attempting to break in traffic I limped back home and took the car to the dealership. The repairs to replace brake pump and cylinder assemblies cost $4,193. 31 but the car was driveable again. However, I noticed that the repairs also corrected the abs problem that was present since the car was new. I think anyone who drives a 2011+ Prius should get their brakes checked for emergency braking where brakes stop working thus allowing the car plow ahead even if the brake pedal is down to the floor.
Tl- the contact owns a 2011 Toyota Prius. The contact stated that while driving at various speeds that the vehicle had issues slowing down. The contact stated that the brake pedal traveled all the way to the floor of the vehicle. The contact stated that the vehicles brakes needed to be pumped in order to stop. The vehicle was taken to the dealer where it was diagnosed that the brake cylinder assembly had failed and needed to be repaired. The vehicle was repaired. The manufacturer was made aware of the failure. The failure mileage was 59,000. Wh.