Brake "Honking" Noise - Bad Actuator Help please

Unfortunately, the noise is almost normal.
It may go a long time without any problems.
You could try changing the fluid to see if that helps

 

There is a warranty extension for this. Did they even mention it? Ask them, mention you'll check with Toyota too, that might help.

I'm not sure what the criteria and time/mile limits are, doubly so in the States, but there IS an extension. If the dealership didn't at least mention it that sounds pretty slack...

For me in Canada it's for sure 10 years since purchase date. There's km's factor too, but I'm way under it.

 

Mine is doing the same thing, should i just use it has it is? no lights in the dash. I think i will just wait until the dash shows that the thing is no more.

 

What could be causing such sound? air in the system or something else?

I live in a quite high place, since when i'm leaving my house to go shopping or something i can feel that my ears clog, so i guess it's a decent altitude. My Prius C 2012 is doing those honking noises as well, it could be the altitude maybe?

 

Well, the original poster had a 2011, and for 2010 and 2011 Prii there was a firmware update described in T-SB-0363-10. When mine was making that noise some I asked the dealer to update that firmware and it helped.

If somebody has a newer Prius, or checks their brake firmware revision and it's already the updated version in the TSB, then something else could be going on.

I don't think I would choose to put up with it for very long. I suspect (though I have done no experiment that really confirms it) that gas bubbles in the brake system are involved, which increases the amount of brake fluid flow needed to reach a certain pressure, and that the honk is some valve in the actuator being played like a saxophone reed by the fluid squirting past. If I'm right, going through the long-form bleed procedure might well help, for some time at least.

It seems Prius brakes can kind of manage to work even with amounts of gas needing bled that would be enough to disable braking in a conventional brake system. So a person could get sort of complacent. An argument against complacency might be that Prius brakes also have a fail-safe mode they can drop into if the electronics mess up, and the fail-safe mode more or less is a conventional brake system, and if there's enough gas in there to disable a conventional brake system. having it ever drop into fail-safe mode would come with an unwanted surprise.

 

My 2013 Prius C just started having the same problem. Brought it to a hybrid diagnostic center and was told I need a new ABS Brake Booster with Master Cylinder. I’m going to try the complete bleeding procedure to see if it helps. Will give an update after I do it.

I’m also interested in the firmware update idea, but only if the bleeding doesn’t work.

In the end, I hope it’s not the ABS Brake Booster with Master Cylinder; I want to avoid having to replace that since it’s an expensive part and labor intensive.

 

I'm not sure there was a firmware update for the issue for Prius c. Just for 2010–2011 liftbacks.

If the long-form bleed procedure makes the honking go away, then you get to wonder how the bubbles you bled out got there. If somebody had the brake system open to work on it, that could be how. Otherwise, they probably were nitrogen slowly leaking from the accumulator, which would mean the issue won't really be fixed until that's replaced, but it may take a good while to recur if the leak is very slow.

 

Does the pump runs constantly? if you open the bonnet with the car on, and as the pump turns on then off, can you see the brake fluid in the brake fluid reservoir change level?

 

Typically, the brake honk noise isn't associated with noticeable extra running of the pump. Those are just two different ways the brakes can go wonky.

Most cases of frequent pump running stem from internal leakage of brake fluid back to the reservoir, so pressure isn't held.

Slow leakage of nitrogen from the accumulator can eventually be its own cause of frequent pump running, but only after the volume of nitrogen remaining in the accumulator is significantly reduced.

 

The pump turns on every 2 minutes and 30 seconds, on average. I can see the level rise very slowly and then decrease when the pump turns on, but the change in level is only about 1 millimeter.

 

Can you hear a hissing sound when the pump turns off?

 

Yeah even without nitrogen i think the pump can work just fine, it will just need to run more.

 

No, there is no hissing sound.

 

As the volume of nitrogen in the accumulator decreases, the pressure change becomes steeper for the same amount of brake fluid moved, so the pump will run shorter and shorter cycles more and more often, just like the well pump in a house with too little air in the pressure tank. Completely without nitrogen, things would get really unworkable,

2 minutes and 30 seconds is not nearly the worst I've seen reported on PriusChat, but it's a long long way from good (which is more on the order of hours). Some people wait till it's mere seconds, before fixing the problem, but at 2½ minutes it's not like you're waiting for confirmation.

It's probably more the people who wait for seconds-long cycles who get to hear a hissing sound. At 2½ minutes the leak is slow enough it might not be easy to hear.

 

Oh, so this is probably the worst brake design, it will become useless once the nitrogen goes out, something that is going to happen before the pump dies or brake lines rust to cause brake issues.

 

Mine was making a hissing sound and the pump was turning on every 2 seconds. Seems like you are still good.

 

I'm not sure how likely it is to happen before any of those other things.

Some of the early 2010 accumulators had defects and would leak nitrogen extra early. Those got recalled.

All the others? It's possible they very slowly leak small amounts of nitrogen into the lines, causing honk noises.

Describing what would happen if one ever lost enough nitrogen to affect pump cycling doesn't mean I've ever encountered or read about one that did. Typically something else happens first.

You waited till it was every 2 seconds and you could hear hissing, but that doesn't mean everybody else has to live in denial quite that long. It's hours for a good one, so every 2½ minutes is already a long way from "still good".

 

I'm a little behind the curve here. Is there an extended warranty relating to the braking system that would include my '14 Prius?

 

That's maybe telling. If I pop the hood on our 10, without opening driver's door, then open the driver's door to activate the pump, I'll see the level in the reservoir drop about 3/8".

The attached might be of interest, but the cover letter only mentions 2010. Might be out of date though.