Noise During Braking To A Stop

that is really low miles for a 2012. does it have a clean history?

can you post a recording of the sound?

 

Sounds normal to me. Prius uses an electric vacuum pump to provide "power" brakes. You'll hear it run when you open the driver's door after the car has been sitting. It will also run periodically during driving, but you'll only hear it when slowing/stopped as you describe. You could check the brake fluid level in the reservoir and make sure the fluid is clean and clear. As long as the brake pedal travel is normal and not "mushy" you should be fine.

 

The brake fluid reservoir tends to be pressurized. Avoid opening the cap until you know the procedure or you may be sorry.

 

Just to clear up a couple things....

Don't look for an "electric vacuum pump" in a Prius. Conventional cars use vacuum (from the engine) to provide your power brake boost. Prius can't, because the engine's not always on, so it uses an electric pump, yes, but not for vacuum. It pumps brake fluid, and pumps it up to high pressure in a storage vessel called the "accumulator".

The reservoir (plastic bottle where you can check and fill the fluid) is not where the pressure is. It's just a plain plastic bottle. You don't have to worry about opening it (except, as with all brake systems, keep that to a minimum, because any humid air you let in contaminates the fluid).

The pressurized accumulator is a separate, very sturdy metal can. In there, the fluid is at a couple thousand PSI. (Medical types may point out that's enough to self-inject right through skin.)

The squirting sounds could indeed indicate the presence of gas bubbles in some of the lines. In a conventional car, that would give you a mushy pedal feel (first you have to compress the gas bubbles before you can transmit any effective pressure to the brakes). The Prius system sort of keeps you from noticing that, because it is electronically controlled and has that whole accumulator of pre-pressurized fluid to work with; it just holds the valve open until it sees the pressure it wants, and if that takes a hair longer while enough fluid squirts through to compress a gas bubble, that's all you notice; you don't feel a mushy pedal as you would in an older car. If a bubble gets big enough, the ECU will eventually set a trouble code about it.

So, if you have the Techstream software and a J2534 dongle and some fresh fluid, you could try going through the bleed sequence and see if the squirt noises diminish.

-Chap

 

Question, do Gen 3 Prii have the rusty rotor noise like the Gen 2?

 

You can do a brake bleed without techstream, setting the car in invalid mode. I can post a PDF tomorrow. Also @NutzAboutBolts has a video on this, pinned at top of this forum.

Not 100% sure this is what @ChapmanF is suggesting, or it is trickier?

Also, I'm starting to hear a brake sound, a slight "grunt", just occasionally, usually a split second before the car comes to a complete stop.

Addendum: Brake Fluid Replacement without Techstream info added. The instruction to put the car in "invalid" mode says to shift to Reverse, but neglects to note you need to push the brake pedal to do this. @NutzAboutBolts does demonstrate the procedure, and does note the need to push brake.The brake bleed order is different in the manual from the video, I think either would work.

 

Generally good post but.......you can NOT compress a liquid. That's why hydraulic systems work.
The compression comes from trapped air.

 

Safety First.
Certain mechanical problems I always just default to go get it checked.
Yes, it may be a cost, but if it saves your life or the lives of others? It's worth it.
Brakes, Tires, Suspension, Steering...
I hesitate to give an evaluation over the internet to a given description.
I would just go get it checked.

You just purchased it a few week ago?
Was it from a dealership?
Toyota Dealership?

You need it to be checked by someone familiar with the Prius regenerative Hybrid Brakes.
If you bought it from a Toyota dealership, only a few weeks ago, maybe they would check it for you as a courtesy, as a newly purchased used vehicle.
Otherwise, it may cost you some money to determine what's going on.
But again, I think that's money well worth spending.

Good Luck...
Be Safe.

 

Some may not believe this, but I really do try to trim posts for length and decide what details will matter to the reader in that particular post. Yes, a pressure accumulator has to contain a compressible medium. The one in the Prius contains nitrogen gas, sealed with an internal metal bellows; regular readers'll remember I've covered that detail before.



(That's not exactly the Prius accumulator, but an example of the construction.)

The compressible gas is all supposed to be sealed in the accumulator; there should be none in the brake lines.

It is possible to have a "mystery" situation where the brake system was once properly bled, and has never been opened since, but now mysteriously can be bled again and some "air" escapes ... if that happens, the accumulator bellows may have formed a small crack, and the escaping "air" is actually some of the nitrogen charge ... in which case an accumulator replacement will eventually be called for.

-Chap

 

Back in August 2013 there was a Canadian notification, to get Brake Booster Pump Assembly inspected, due to possibility of nitrogen leak. Ours got replaced at the time I think, looking at the dealership invoice. Maybe they're continuing to be problematic.

Who has had brake actuator and pump failure - 2010 Prius? | PriusChat

 

Much like your pressure tank if your house has a well. Different volumes and pressures, but same principles.

 

yes

 

If I've washed the car, then just rolled it back into the garage and it's sat for multiple days, that seems to be the worst scenario for surface rust on the rotors. The next time I go to drive it the brakes are noisy for the first block or two. But it clears up fast, back to quiet after that. That's pretty much normal I think.

 

I have the same problem. After retiring my 2006, I bought a 2012 with about 100k miles. Frequently, when braking, I'd hear one short sound when the pedal was fully depressed. I'd call the sound a...um...squelch.

Shortly thereafter, someone ran a red light in front of me and I totaled the car. I bought another 2012, also at around 100k which presents the exact same sound, if somewhat less often. The brakes do, and did, work fine, apart from that.

 

I'll just mention here that I'm forming the beginnings of a suspicion that too much squelching over too long a time could lead eventually to a sudden and unexpected brake malfunction. It's nothing yet beyond a speculation on my part, but there it is. I would not go hair-on-fire alarmist about it, but if it's possible to go through a bleed sequence and there's any trapped gas that escapes, I think that would be worthwhile.

 

In other threads I've followed up to this, but I see I didn't here.

There is a non-Techstream procedure in the manual for fluid replacement, not for bleeding. You go through very similar motions, but you're doing a fluid replacement if you are sure there are no bubbles to be gotten out and all you want is to exchange old fluid for new.

If there is any chance there are gas bubbles in the actuator needing out, what you need is the bleed procedure in Techstream (specifically: the longer of the two bleed procedures in Techstream).

The reason is that there are multiple hydraulic paths to the front brakes, and no matter what YouTube personality's clever non-Techstream "bleed" procedure you follow, without Techstream switching those valves around for you, you are only bleeding one of those paths, and in fact, you're only bleeding the one that normally isn't used.