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Frequent Brake Vacuum Booster Noise

Discussion in 'Prius v Care, Maintenance and Troubleshooting' started by Glenaby, Dec 8, 2023.

  1. Glenaby

    Glenaby Junior Member

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    I very much appreciate this Forum and the support from members! I searched and found what would likely be something wrong with the Brake Vacuum Booster on my 2015 Prius V with 73k miles.

    In addition to the normal noise, but with a frequency of about every 15 seconds, the brakes seem more sensitive when applying quick braking, but also when coming to a slow stop with light braking you can feel the brakes (and car) pulsing.

    I am the second owner, and as best I can tell the car has never had any work done on the brakes.

    Is this a troubleshoot/probable repair for only at a dealer, or should any place that works on Toyotas be able to correctly handle this?

    Also does anyone have recent history or an estimate for what the typical repair would cost?
     
  2. ChapmanF

    ChapmanF Senior Member

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    A Prius cannot use vacuum to boost the brakes, because the engine is not always running to pull a vacuum.

    So the Prius does not use vacuum in the braking system for anything. Instead, it uses an electric pump that pumps brake fluid to high pressure in a nitrogen-filled accumulator.

    The pump sounds a bit like a rattlesnake, or a joy buzzer. From your description, the pump is probably what you are hearing.

    When the brake system is in good condition, you will only hear the pump every few times you use the brakes. If the brakes are not touched, you should be able to sit in the car and read short books between runs of the pump.

    If you are hearing the pump run more often than that, and especially if it is as often as 15 seconds, the system is in poor condition.

    There are two assemblies under the hood:

    [​IMG] (Because of some PriusChat breakage from the recent server migration, that image doesn't show up. You can view it here.)

    The lower one in the drawing contains the pump, but the upper one contains most of the valves in the brake system. When the pump is running often, even though the sound you hear is from the lower unit with the pump, the problem is most often in the upper unit with the valves. One of the valves may be allowing some brake fluid to pass when it should be completely closed, and the pump needs to run more often to make up for it.

    People for whom cost is no object might just replace both assemblies at once and avoid having to think further about which one has the problem. Others will usually start with the unit on top.
     
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  3. V Sport Wagon

    V Sport Wagon Member

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    That year and that mileage should be covered under Dealer Warranty. There's a TSB for it.
     
    Brian1954 likes this.
  4. Glenaby

    Glenaby Junior Member

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    Thank you. I found the TSB. I saw some posts mentioning this as well during my searches. In my case, I don’t have any errors displayed on the dash. I’ll have it checked out at a Toyota dealer just in case.
     
  5. Mendel Leisk

    Mendel Leisk Senior Member

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    RCMN-13V235-0909
    RCMN-13V235-9056

    ^ These are the numbers on the pdf format TSB's I cadged. You could search for those. I'd post them, but that's no longer possible, since the server replacement.
     
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  6. rjparker

    rjparker Tu Humilde Sirviente

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    Here is one version of the Toyota extended support on the brake booster. However Toyota requires one of the codes. The typical repair is $2500.

     
  7. Glenaby

    Glenaby Junior Member

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    I wanted to followup and provide an update. Shortly after posting this, I took my car to a dealer close to me. I reported what I originally documented in this thread, and to my dismay, the SM said the Tech could not duplicate anything, but also no error codes or lights in the dash. I was puzzled by this since I could easily duplicate both symptoms as I was leaving. Had they said the parts need to be replaced, I might have done it at my cost. I decided to just let it go, as they were possibly doing me a favor.

    Fast forward to last week, and while coming to a stop, something happened and 4 of the 5 documented error lights came on, and the brakes required more pressure to stop. Now the pump noise occurs every 2-3 seconds. This time I took it to a different dealer, and they confirmed it is the failure and it would be fixed under warranty. I recall the SM telling me it would cost 2000+ if it wasnt warranty.

    I picked it up late this evening, and the paperwork shows two parts were used as follows:
    04000-23876, Brake Cylinder Kit
    04006-22212, Brake Pump Assembly

    I was expecting what ChapmanF described in his post above. Can someone that knows this repair share their thoughts? I am curious what the brake cylinder kit is, as I can find no photos when I search on the pn.

    BTW, in my pn searches, it appears both of these list for just under $1000 each although several dealerships show them on sale with several hundred dollars off.

    Thanks
     
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  8. rjparker

    rjparker Tu Humilde Sirviente

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    You are getting the best. Chap likes the master cylinder only; when mine went out years ago I got both and its good to know both parts were new. I now have more miles on the warranty parts than I had when the original parts failed. Some guys want minimum, Toyota and I prefer reliability.
     
    Tim Jones likes this.
  9. ChapmanF

    ChapmanF Senior Member

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    I'm not sure it's a matter of what I 'like' ... I've mentioned before that Toyota changes both parts, and that's what you'd do if money's no object. Sometimes people post who are outside of the free replacement coverage and who say that money is an object for them, and to those people I'll say that if you're going to start with one part or the other, the odds are on the upper one (brake booster assembly, also known as master cylinder) because that's where most of the little valves are to wear out.

    As to the question in #7, that upper part ("brake booster assembly" in the drawing) is also known as the master cylinder. And it's also known as the actuator, and as the skid control ECU. In gen 3, all those things are in that part.

    The part number prefix of the booster/master cylinder by itself is not 04000-, it's something else (47050-, I think?). 04000- prefixes are for "kits" that include a thing itself and some other stuff, like a gasket maybe, that you're going to need when you change it.

    It's useful to know the part numbers for those kits, because sometimes the kit price is lower than the price for the thing by itself.
     
    Tim Jones likes this.