*Median odometer reading when the problem happened, where owners gave one. One complaint can name several problem areas.
Service brakes
I was driving the vehicle and a bunch of dash lights came on regarding traction control and stability and lost all brakes and almost caused an accident! The codes thrown showed a fluid level indicator and a leak in accumulator
Oct 26, 2026Service brakes
I was driving on the highway when my 2011 Toyota Prius started beeping repeatedly, and as I approached the red light, my brakes were not operational. My car completely passed through the red light, narrowly missing what could have been a fatal accident for me and others on the road. I had to navigate to the furthest right lane, almost getting hit by others due to my speed and inability to stop my car. I was going at 50 mph through the intersection, and had to gradually lower my speed in the righthand lane. The Toyota dealership confirmed the issue with my brake accumulator, with a C1391 code. The only warnings were the brake light in the moment and the repeated beeping noise. To stop the…
Sep 29, 2026Service brakes
2011 Toyota Prius with approximately 134,000 miles. The brake actuator/master cylinder has been diagnosed as malfunctioning and failing to maintain hydraulic pressure. The brake booster pump initially began cycling approximately every 10 seconds while the vehicle was in READY mode, stationary, and without the brake pedal being applied. The cycling subsequently increased to approximately every 3 seconds. The affected components remain installed and are available for inspection upon request prior to repair. Because this condition involves the braking system, I am concerned about the potential for reduced brake assistance or further brake system failure, as well as excessive wear on the…
Sep 2, 2026Engine
Coolant leak into the engine, confirmed by the Toyota servicing center. This may be a common problem with the Toyota Prius, causing early engine failure from a design defect.
May 4, 2026Service brakesCrash
I am filing this complaint to report an active, severe safety defect involving a sudden, un-warned loss of power braking assist due to a failing factory brake actuator/booster pump assembly. My vehicle is exhibiting the exact internal hydraulic seal failure, pressure drop, and audible hissing/sipping sound outlined in Toyota's prior technical service bulletins. Because the onboard ECU computer only triggers warning lights once a complete, catastrophic failure threshold is met, the system is currently masking the defect from the dashboard. However, the physical hardware is actively failing, requiring the high-pressure pump to run constantly to maintain braking pressure. This component…
Sep 11, 2026Service brakes
Vehicle Information: 2011 Toyota Prius, 144,000 miles. Component: Hydraulic Service Brakes, Electronic Stability Control, Anti-lock Braking System. Description of Incident: While driving at normal speeds, the vehicle suddenly experienced a severe reduction in braking capability. The dashboard simultaneously illuminated the Brake Warning Light, ABS Light, and Slip/Traction Control Indicator Light. The brake pedal immediately became soft, spongy, and squishy, requiring significantly increased physical foot pressure and a vastly extended distance to bring the vehicle to a stop. Upon inspection, the brake fluid reservoir remains completely full, but the brake booster pump under the hood cycles…
Aug 7, 2026Service brakes
Every time I'd press the brakes there'd be an audible "click" noise and then when taking my foot off the brake it'd sound like a manual tire pump being pressed... kind of like air filling / hydraulic sound. This worried me (I don't mess around with brakes). One other thing that would happen is if I pressed the brake hard enough, the automatic braking system would kick in. The Toyota dealership claimed they couldn't hear anything and there were no warning lights so I took it to a reputable local mechanic. They diagnosed it as a bad ABS Actuator / Brake Booster and said it's common with this year of Prius. They also said it was good I brought it in now because it was not severe enough to…
Jul 1, 2023Service brakes
Vehicle Information: Year: 2011 Make: Toyota Model: Prius Mileage at Failure: 58,769 miles Date of First Use: February 20, 2012 Complaint Description: As I was driving on the freeway, my 2011 Toyota Prius brakelights all came on. I pulled off, had it towed to nearest mechanic, who diagnosed a failure involving the brake booster, brake actuator, and ABS system at only 58,769 miles. The vehicle was diagnosed with Diagnostic Trouble Code C1391 (Abnormal Leak of Accumulator Pressure). According to my mechanic, the condition is caused by an internal brake fluid leak within the brake booster assembly with master cylinder. The recommended repair includes replacement of both the brake booster…
Jan 15, 2026
Owner complaints are submitted to NHTSA by the public and are not verified. Shown as filed (NHTSA removes personal details); long reports are shortened.
