My Prius, along with the thousands of others this has apparently happened to according to a quick online search, has had the C1391 code appear, indicating a failed brake actuator and accumulator. It, like the thousands of Priuses from this generation, have had these faulty brake pump systems develop a leak and begin to fail. You will hear a whirring and hissing noise constantly when it starts going out, eventually resulting in a Christmas tree of dash warning lights and reduced braking due to a failsafe kicking on. Toyota apparently issued a ‘customer service bulletin’ that is now ineffective as it only covered if you had the system fail within 10 years of manufactor or 150,000 miles AND had the codes appear. Most people’s Priuses go out AFTER this, unless you’re driving it like you stole it. It is a hefty repair too, being quoted at over $3000 at the Toyota STEALSRSHIP!! I have since gone to an independent mechanic and had one portion replaced in hopes that would fix the issue, but it turns out both the actuator and accumulator are needed to be replaced, which is extremely expensive, more so for the actuator than the accumulator, but still exorbitantly expensive. In conjunction with this, Toyota further added difficulties by making their paet numbers they have listed different from the mark number engraved on the part, so buying third party is made a bigger hassle by this as they will not know for certain the part number. This is a huge safety concern as this affects the vehicle’s ability to brake. Their service bulletin was the equivalent of offering people bandaids years before they’d be anywhere to getting a cut!! Please investigate and please please PLEASE lead to Toyota issuing an actual recall, regardless of miles or year from manufacture. More and more Priuses are reaching the time where this will occur and it’s a huge safety concern, if not an environmental concern when people start disposing of Priuses due to this massive failure with hefty repair bills.