Is this noise normal ?

Doesn’t sound right at all

 

You are pressing the brake repeatedly, which repeated brake actuation releases pressure, which eventually causes the pump to recharge the accumulator.

 

Have you bled the brakes and/or are you losing brake fluid?

 

honestly, i have no idea. i only know that mine never made any noise except for the occasional buzzing

 

Noise could be air bubbles in the fluid, coursing through the valve. But if you don’t feel a soft pedal, it’s not a functional problem.

 

I haven't listened to the clip (the site, clipchamp.com, isn't one I've used before or wrestled with my browser settings to allow videos from) but if the noises are sort of squishy/squirty and buzzy/honky, then bubbles are probably the cause.

If so, they should all be carefully bled out. "if you don’t feel a soft pedal, it’s not a functional problem" is an old rule from old cars; if they needed air bled out, you would know because the pedal would feel soft.

A Prius doesn't work that way. The pedal only feels the way it does because of a stroke simulator, and the brake computer is what applies the brake fluid to work the brakes, and if there are bubbles, it just shoots more fluid in, enough to compress the bubbles and reach the target pressure. You don't feel anything different on the pedal (though you might hear the squishy/squirty sounds from the extra fluid having to flow).

There are a lot of nice things about that system, but also a not-nice thing, which is the way it keeps you from noticing when there's air in the system. There can be a small, medium, or large amount of air and the pedal doesn't feel any different and the car stops the same, other than the squirty noises you might hear if you're paying enough attention.

So if the pedal feels the same and the car stops the same anyway, why care? Well, the system also has a fail-safe mode. There are things that can go wrong that will put it in fail-safe mode, where it really is just your foot on the pedal moving the brake fluid, and at that moment you do find out if there's air in there, 'cause the car won't stop.

So the safe approach is, before that ever happens to you, if you are hearing signs of air in the system ... get that out.

 

No but you should record it at the brake booster, not inside.

 

So, "if you don’t feel a soft pedal, it’s not a functional problem", but for a different reason, unless it goes into manual reversion.

 

If you would regard floored-brake-pedal-no-stoppie as a functional problem, then having unbled air in a brake system is a functional problem. Any of multiple related or unrelated causes could switch the system into fail-safe mode at any time you don't expect, and if there's air you've been ignoring in there, you won't like the way that story ends. There are floored-pedal-no-stoppie incidents reported here on PriusChat, and among NHTSA complaints, and in lawsuits IIRC. It is a failure mode that happens.

If you're of the philosophy "seems to stop ok right now" = "no functional problem", you're probably safer in another car with simpler brakes. Those won't ever seem ok with air in them, so you wouldn't be tempted to ignore it.

An unintended quirk of the Prius system is that it can "seem to stop ok" even with significant bubbles in the system ... until it doesn't. So you can be tempted to shrug off the presence of bubbles even if you know about them. It just isn't a good kind of problem to shrug off.

 

In that clip, I really don't hear anything that bothers me much.

I hear a brief hissy noise on pressing the pedal, but it is not like the longer hiss/whoosh you can hear when there are large bubbles having to be compressed. It sounds roughly normal to me.

Also, you are getting a good three pedal strokes between runs of the pump, which I think is pretty normal. Significant bubbles would tend to make it run more often. (With bubbles, more fluid has to leave the accumulator when you apply the brakes, to take up the bubble space and reach the target pressure; then, when you release the pedal, the bubbles re-expand and shoot that extra fluid back to the reservoir. Upshot is, more fluid used with each pedal press, so the pump has to run more often.)

And I don't hear any honk/bark/grunt/quack noise (people have used all those descriptions), which sometimes comes along with bubbles in the system (I think one of the actuator valves gets worked like a saxophone reed when the bubbles re-expand and shoot the fluid back).

So I would say you are missing any of the signs that would concern me about bubbles. I'm feeling ok about that.

Was that faint high-pitched whiny noise the other thing concerning you? It's not a noise I've noticed myself, but it doesn't sound disturbing to me. Maybe I've never recorded mine up that close. I'll assume there's something the brake ECU does using a pulse train, and its frequency is that pitch you're hearing.

I only hear that sound while your pedal is pressed. One easy thing to try would be to hold the pedal pressed, and then use a finger to press/release the brake light button up by the pedal pivot. That at least would show whether the sound really depends on that switch, or on the pedal position itself.

 

I’ve had the v go into manual reversion when the ABS kicked off due to an intermittent OBD2 reader connection. It stops, but not with the normal regeneration and power assists. Foot pressure required is dramatically higher and braking rate reduced. Like many things in other cars, you drive around the problem until able to diagnose and solve the problem.

 

What you have experienced is the fail-safe mode working as intended. Many other people have experienced that too.

The presence of unbled bubbles in the system can allow you to also experience the fail-safe mode not working as intended. Other people have also experienced that; it is (thank goodness!) more rare, but you can find PriusChat posts and NHTSA reports and lawsuits describing it. In that failure mode, foot pressure required is not harder; the pedal goes easily to the floor, and the car keeps going.

If you have not experienced that failure mode, thankfulness is in order. To avoid ever having to experience it, it is good to make sure any bubbles in the system are bled out at the first sign they are there, even if they don't seem to be causing a "functional problem" at the time.