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Discussion Starter · #1 ·
Dear Experts;
I've read the other posts about this "whirring noise" and understand that it can be the coolant pump or the brake accumulator. But, I'm hearing this noise way too often.

I have a 2005 with only 450 miles on it. I've driven it mostly with the radio off so that I can hear how quiet it drives and get accustomed to all the little noises it makes. Today...for the first time...I started hearing the whirring noise EVERY 2nd or 3rd time I step on the brake pedal...all day long. In fact, I had the radio on quietly and kept hearing a noise and thought it was on the radio until I realized what it was.

When I parked my car (before powering off), I stepped on the brake pedal repeatedly. Every second or third push I would hear the whirring noise for about 5 seconds....the same as when I was driving.

I have never heard this noise prior to today.

I'm not panicking, but since I could not find a description on this forum that described this as happening so often I thought I would ask.

Thanks!
Jeff
 

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As long as you do not get a red brake warning idiot light the system is safe to use but it is not normal. You have either a discharged gas charge in the accumulator or an internal leak in the hydraulic system if there is no sign of fluid on the garage floor.

I'de get it to the dealer first thing as it sounds as though your hydraulic pump is operating much too often and it isn't designed to do so.
 

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Could the whirring just be the regenerative braking? That sounds like what you are describing and it would happen very frequently, especially when only lightly braking. If you brake more agressively, the friction braking would do more work and you might be less likely to hear the sound. I'm thinking this because it is a new car and does have sounds that most people wouldn't be used to. It isn't the case that the car used to not make the noise and now does.
 

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Discussion Starter · #4 ·
Actually....when I'm braking "lightly" I don't hear it as often as when I brake more heavily. BUT....I did notice a few times that I heard it the moment my foot touched the brake pedal.
 

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Discussion Starter · #6 ·
Just got back from the dealer. The Tech listened while I was able to reproduce it stepping on the brake pedel three times. Then we went for a ride and he heard it and basically said "unless there are lights displayed on the dashboard" don't worry about it. He said it was coming from the ABS Actuator. I'm not sure I'm real comfortable because if it continues trying to keep up pressure so often, perhaps there is a leak. I now am noticing it sometimes when I realease the brake and start to accelerate.

I guess I'll just wait and see what happens. He did say that these vehicles are incredibly reliable and if anything does fail, the lights come on and there are a host of diagnostic codes to pinpoint the problem.

Jeff
 

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There is a thread (here or on PC) that contradicts the idea that there can be nothing wrong with the brake pressure system without a warning lamp lit. A slow leak can give these symptoms.

Brake problems don't make me think of warrantee coverage, they make me think of life insurance coverage!
 

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Three long, hard presses of the brake triggering the accumulator sounds normal to me. However, it should not come on if you are just holding down the brake (not pumping).

I'll check tonight how many presses of the brake at a standstill triggers the accumulator pump.
 

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Discussion Starter · #9 ·
Thanks DanMan! I just found a previous thread called "What's That Buzzing-Part 3" that really sounds identical to the sound I'm hearing...although I'm not having a "pedal sinking to the floor" problem. However, in this thread the problem WAS the accumulator. I've printed out this thread to take to my dealer if this problem persists or gets worse.

If you (or other people confirm) that three firm presses on the pedal cause the accumulator to turn on...it sure would make me feel better. Still...I will keep an ear on how often I hear the pump running in my normal course of driving. CERTAINLY I'm hearing it more often over the past two days than I had before.

On another topic (and since you seem to be the "Prius God in this forum"...is there anyplace in this forum where we might post all the Q&A, sounds, symptoms, quirks, etc. that a new owner would experience so that perhaps people like myself wouldn't have to bother you folks with redundant threads? I would also love to know how you personally learned so much about this vehicle...whatever you read I would like to find it :D

Thanks again for all of your help!

Jeff
 

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Prius_Technical would be such a forum.

But I understand what you mean. The original PriusChat had a KB, and the new one does too, but it has gotten unmanageable. Still might be nice to have simple symptom topics with probable solutions. Maybe a few sticky topics?
 

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Danman had suggested going out and testing our own cars. So, out to the garage I went and gave it a test. My garage is about 50 degrees right now, so not too hot, not too cold.

Anyway, with the vehicle powered down it took a good hard 4 or 5 pumps of the brakes to activate the accumulator. Consider, that dry pumping the vehicle without the vehicle on is not going to be a true replication of how the braking system works while driving.

But I'm hoping to reassure you that your system is probably just fine, my vehicle does run the accumulator after a stop while pulling away from the stop. I might pay more attentiont to it now for a while to see how often it runs while driving.
 

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I didn't do an extensive test, but I found that the accumulator would come on after 3 pumps, with me pressing down hard after the 3rd pump. If I let up on the brake, the pump stopped.
 

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Discussion Starter · #13 ·
Gee....now I see why Prius owners "unite!" :D

It's nice to hear that all three of our vehicles seem to operate the accumulator pump about the same...at least with the standstill "pumping." And, I'm glad that Jeromep has said that he hears his pump come on when accelerating from a standstill....this too sounds similar to what I'm finding. I will certainly keep listening for it on my long trip next week to be sure it doesn't get any worse. I do agreee with DanMan, however, that if it comes on too frequently it has to mean some kind of leak.....and after spending hours going through previous threads it does sound like several folks have resolved this with Toyota by replacing the accumulator. But..I'm not jumping to conclusions yet. If anyone else does the "test" it would be nice to have more datapoints.

Oh...I called the Toyota 800 number yesterday just to see if I could get information about which dealers have the most experienced Techs on this vehicle...and I mentioned I might have a brake problem...and the conversation was kind of what I expected. "We cannot recommend one dealer over another, but you can go to the Toyota website and view dealers in your area and see if any of them have received the President's Award." This wasn't very helpful at all and when I tried to stress that I was concerned about the brakes, I still got no further. Well...one step at a time. Thanks to all of your for assisting with this test.

Jeff
 

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Keep in mind that if the accumulator is running while you are cruising down the road with no brake activity, a problem probably exists. The same can be said if you are in park someplace with the vehicle on. The accumulator shouldn't go through its repress unless the system needs it. It should only need to do the repress if brakes have been applied and the lower limit of pressure has been reached with that brake application. That is my understanding of how the system works, in the grossest terms.
Now, as for Toyota recommending dealerships, they can't do that without creating havoc between Toyota manufacturing and Toyota sales operations. However, the various corporate awards, such as the President's Award, although they appear to be fluf, can point you in the direction of a dealer who has met certain customer service standards, as determined by corporate. The rep you were talking to was basically saying, the PA dealers might be better than those that have not earned the PA.

My local dealer doesn't seem to have any Toyota awards, however my selling dealer has won the Presiden'ts Award, and in general I can tell the difference. It isn't that my local dealer isn't competent with the vehicle, but there are just small touches in how they treat you that make all the difference and are probably what makes one dealer a PA dealer and another not.
 

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jeffndallas said:
Dear Experts;
I've read the other posts about this "whirring noise" and understand that it can be the coolant pump or the brake accumulator. But, I'm hearing this noise way too often.

I have a 2005 with only 450 miles on it. I've driven it mostly with the radio off so that I can hear how quiet it drives and get accustomed to all the little noises it makes. Today...for the first time...I started hearing the whirring noise EVERY 2nd or 3rd time I step on the brake pedal...all day long. In fact, I had the radio on quietly and kept hearing a noise and thought it was on the radio until I realized what it was.

When I parked my car (before powering off), I stepped on the brake pedal repeatedly. Every second or third push I would hear the whirring noise for about 5 seconds....the same as when I was driving.

I have never heard this noise prior to today.

I'm not panicking, but since I could not find a description on this forum that described this as happening so often I thought I would ask.

Thanks!
Jeff
From an automotive engineer with direct experience with this technology:

What you have described is NORMAL. Hydaulic assist (like a vacuum booster only it uses brake fluid under pressure) is used to boost the brake fluid pressure for hydraulic braking, ABS, Trac, VSC, etc. The accumulator has a nitrogen gas precharge, and is then filled with brake fluid to about 2000 psi, the fluid seperated from the gas by a diaphram. A motor attached to the hydraulic brake modulator pressurizes this fluid. When you depress the brake, brake fluid is displaced which reduces the pressure in the accumulator until it drops below a switch set point and the motor starts to recharge the accumulator. Some may recognize this as "hydraboost" on some other vehicles. With the Prius, until the brakes begin to supplement the regen braking with actual friction braking, no fluid is displaced from the accumulator. The harder you brake, the more fluid that is displaced as a result, thus increasing the frequency of the pump runs. The volume and tone of the pump will change with temperature and altitude. This results due to fluid viscosity change which affects the load on the pump as well as less atmospheric pressure which increases the affective accumulator precharge pressure, which again affects fluid volume and pump load.

Maybe this is too much detail, or not enough. Anyway, your EHB (Electro Hydaulic Boost) brake system is operating normally. A small amount of interior noise, such as the radio or HVAC fan, will mask most of all of the pump noise. As an asside for those interested, the pump noise in the Prius is tuned using a large iron block which can be found hanging on the bottom of the modulator. About 10 pounds worth if I recall correctly.
 

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Mdacmeis, Great post. You should be modded up on the forum.

Didn’t quite understand this part though:

mdacmeis said:
As an asside for those interested, the pump noise in the Prius is tuned using a large iron block which can be found hanging on the bottom of the modulator. About 10 pounds worth if I recall correctly.
Not sure if you were kidding… Are you saying there is a 10 lb iron block attached to alter the acoustic characteristics of the pump? Is it shaped?
Interesting. Why not just use a 10 lb heavier pump, presumably with better acoustics? Or insulation?
 
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