Table 1 shows one common forward collision avoidance related problems of the 2015 Toyota Prius.
| Problem Category | Number of Problems |
|---|---|
| Automatic Emergency Braking problems |
The abs failed while driving on the highway. There was no accident, but it was substantially harder to brake when needed.
While driving, my brakes became mushy and ineffective. Brake warning lights came on, also. It was very scary driving in rush hour traffic with little to no brakes. There was no reliability. Just keeping as much as possible space between cars, using hazard lights &prayer.
Failure of brake pump and brake cylinder assembly system, resulting in reduced braking ability and stiff brake pedal. Per Toyota's diagnostic: trouble code c1391 is present, abnormal leak in accumulator, replaced brake abs actuator assembly, along with brake master cylinder, and bleed the brake hydraulic system. No warning lamps or safety indicators prior to failure. Upon failure (while on freeway going 50+ mph) the abs, brake, and traction control warning lamps illuminated. The failure resulted in no accident or injury, however it did occur while on the freeway going freeway speeds, and resulted in difficulty in braking, which was dangerous. Took Prius into Toyota dealer for diagnostic and repair, was told that part was known to fail in this model of Prius, and had a manufacturer designated extended warranty for 10 years or 150,000 miles. However, despite Prius being under 150,000 miles, it passed ten years since purchase in March 2025, meaning I had to pay in full for the repair ($3,631. 96). The car gave no indication of needing the repair until the day of the failure, which was on June 18th 2025. If the vehicle had given some prior indication of brake pump system failure or fault I would have had it repaired prior to the warranty expiration, but it did not, leaving me to pay out of pocket for a failed part that Toyota is at fault for making prone to failure.
In June 2025, while driving on the highway, the vehicle suddenly displayed multiple brake warning lights and warning messages, including the red brake warning light, abs light, brake system warning light, and traction/slip indicator. At the same time, the brake pedal became stiff and braking effort increased suddenly, creating a near-crash situation because the vehicle did not slow normally. Before that incident, the vehicle had already been making abnormal brake-related noises, including a humming/pumping noise when the brake pedal was applied, and there were intermittent episodes where braking felt abnormal. In June 2025, the vehicle was taken to a Toyota dealership during Toyota’s brake booster support program period. The dealership documented customer complaints of “humming noise in cabin when holding foot on the brakes,” a request to “scan for codes for zjb enhancement,” and that the “vehicle hard to accelerate and brakes got stiff,” but stated that no qualifying abs codes were present at that time. In March 2026, the same condition returned and worsened. The vehicle again displayed the red brake warning light, abs light, brake system warning light, and traction/slip light, and braking performance was reduced. An obd scan of the abs control unit showed code c1391, which is associated with brake booster / abs actuator failure. The Toyota dealership has now diagnosed the vehicle with abs actuator and brake booster failure and quoted repair. This is a serious safety issue because braking became more difficult while driving, including on the highway, with sudden warning lights and degraded stopping ability. The failed components are available for inspection. The problem has now been confirmed by a Toyota dealership. The issue was reported to a Toyota dealership during the prior support-program period but was not confirmed then.