2010 Prius - Leaking accumulator/Check Hybrid System P0AA6

Discussion in 'Gen 3 Prius Technical Discussion' started by DSK7, Oct 14, 2025 at 11:58 PM.

  1. DSK7

    DSK7 New Member

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    Greetings,
    New here...looking for some help with the problems in subject line. Any advice, directions etc are appreciated. Not very familiar with hybrids, but trying to learn.

    2010 Prius w/ 235k miles

    Problems/conditions:

    -The brake booster pump (correct term?) runs/cycles every couple seconds until car is turned off. I can hear a noise in the area of the brake booster when car is off, and the car has shown before the trouble code related to the leaking accumulator (but oddly is not showing it now).

    -Separately, car constantly shows "Check Hybrid System" and has the P0AA6 code. Upon first startup, I can drive it with no abnormalities for a short distance (1/4 or 1/2 mile) but then something strange happens: the brakes no longer will regen correctly while braking, and the traction battery level indicator begins to drop noticeably. It should be noted that there is no braking trouble prior to this happening, everything is normal until the trouble begins.

    I note that once this braking trouble occurs, as I brake or coast, instead of it registering on the regen bar as normal, it indicates on the right side of the regen bar, as though I was using power while braking/coasting. I hope I'm writing this clearly. I'm guessing this is a direct result of the leaking accumulator?

    -Traction battery is only several months old (GreenTec auto) and charged; I have a grid charger to keep it full. But the CHS message displayed both before and after the new battery.
    -12V battery a month old and charged.
    -Getting frustrating.

    Questions:

    1. Can a leaking/malfunctioning brake system in these cars lead to/cause a HV battery isolation fault, seeing that the regen system is connected to the battery in some way? I wonder if these 2 troubles above are related in cause.
    2. I don't have Techstream to read the P0AA6 subcodes; can someone direct me how to get it on a laptop?
    3. Are there any known 2010 Prius isolation fault items I could check right away to eliminate anything off the top?
    4. Brake accumulator: where to obtain besides Toyota? Any refurb units or any such options out there?

    Thanks for any assistance. I've used this forum in the past and am grateful for the previous advice, now would be so glad to get some help on these specific problems. I confess I have not yet fully researched these 2 problems on this site yet. Hoping someone has experienced this before.
    Standing by to give more info if needed.
    Thanks, Eric
     
    #1 DSK7, Oct 14, 2025 at 11:58 PM
  2. ChapmanF

    ChapmanF Senior Member

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    You have two different issues. The often-running booster pump and the code for leaking brake pressure are a simple mechanical issue with worn-out mechanical brake parts. These parts commonly wear out. Many were even wearing out much earlier than they should have, and Toyota had a service campaign for that, but it's over now. Wearing out in a fifteen-year-old car with 235k miles is just wearing out.

    Usually the cause of that problem is in the upper item of the two shown here.

    [​IMG]

    Many people with the problem will replace just the upper item and find the problem fixed. Sometimes it's the lower item. Some people, budget permitting, will just replace both items to not have to think about it.


    Your P0AA6 code indicates a completely different issue. You are noticing an effect on braking only because the brake system is notified of hybrid-system trouble codes, so it knows not to try to do regen. That's the only connection, though; the high-voltage isolation fault is otherwise nothing to do with the brakes.

    Techstream isn't the only way to read the INF subcodes. There are other scan tools or phone apps that can do that. Autel AP200 gets a fair amount of good press around here.
     
    #2 ChapmanF, Oct 15, 2025 at 10:29 AM
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