Any way to confirm need for Brake Booster Repair on Gen 3 Prius w/out codes?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Chase B, Oct 31, 2025 at 1:54 PM.

  1. Chase B

    Chase B Junior Member

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    I posted this on Reddit before coming here for some reason, so I apologize in advance for the double post if you frequent both forums. The title essentially is the question: I have a 2012 Prius with 240k miles, so outside both parameters for the TSB replacement of the brake booster/actuator. The past couple of months when driving the Prius the pump sounds like it runs pretty much nonstop, and I have gotten the honk noise a couple of times when hitting the brakes. That being said, I have not yet had any sort of engine code pop up.

    I purchased the parts to replace when they were on sale at a dealership last month and have been waiting to replace, as it sounds like the booster/accumulator repair needs to be done, but I'm definitely a little hesitant to tear into what will probably be my biggest DIY challenge so far on the Prius if it's not necessary. Absent a code, is there any way to confirm the repair is necessary without the engine code popping up? I have purchased a TopDon TopScan Pro to do the bleed/linear offset procedure when the parts are replaced, so if it's helpful to have an advanced scan tool I should have one that can work. One note; 10 years and 240k miles and I've never touched the brake fluid, so if this is something that could potentially be helped by a flush and refill/bleed I'd be happy to try to that first.

    Thanks for any advice you might have!
     
    #1 Chase B, Oct 31, 2025 at 1:54 PM
  2. Madmommymelinda

    Madmommymelinda Junior Member

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    Ive seen and tried a procedure (maybe on youtube) that suggests an old school bleeding method will at least get you by. Ive tried this and it didnt work. Ive done this repair several times for the same vehicle because I tried to save money by getting parts off ebay vs the dealer. Unfortunately I am still learning my lesson as I am in process of doing the repair again with what will be dealer acquired parts unless someone has some recommendations that could save me $500 to $1k. When the accumulator is accumulating every so many seconds, its only a matter of time regardless of any codes not present. It sounds like you are getting ahead of the inevitable. The trickiest part is rerouting the brake lines as they were. Take good pics to help yourself out. Top don top scan pro will do the job.
     
    #2 Madmommymelinda, Oct 31, 2025 at 4:23 PM
  3. ChapmanF

    ChapmanF Senior Member

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    Careful with the terms, as a gen 3 has two contraptions under the hood:

    [​IMG]

    When you say 'booster' you're talking about the upper one, and when you say 'accumulator' you're talking about the lower one.

    The sound you're hearing is the pump in the lower contraption, but it's quite possible the only reason it's needing to run so often is because of an internal leak in the upper contraption. Often, replacing just the upper one will solve the problem. (A "money's no object, just get it fixed now" type might replace both for good measure.)

    Which part(s) did you buy?
     
    #3 ChapmanF, Oct 31, 2025 at 5:40 PM
  4. BiomedO1

    BiomedO1 Senior Member

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    A two person brake bleed would be prudent. This would at least flush out the system, before replacing it with the new unit. You'll probably find some sludge at the bottom of your reservoir. Use a turkey baster to remove as much of that as you can before flushing system. Mark your recovery bottle a few mL less than your reservoir, so you don't accidentally empty it.

    Good Luck.....
     
    #4 BiomedO1, Oct 31, 2025 at 5:47 PM
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