2011 Prius - C1391: Abnormal Leak of ACC PRESS

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by ninthtale, Sep 16, 2021.

  1. ninthtale

    ninthtale New Member

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    My Prius with a rebuilt title has thrown the ABS, Traction, and Brake HUD lights all together. I took it to an Autozone and scanned the code to get the C1391: Abnormal Leak of ACC PRESS error. In addition to the warning lights, while the car is turned on (driving or not), there is a one-second pump sound whirring, repeating about every two seconds or so.

    I checked around, made calls to Toyota. Since my title is rebuilt, I do not qualify for any extended warranty benefits, so I won't be able to get anything replaced for free. There is a software update available for which I have an appointment next week, but that's all I was able to get.

    I also found this thread on PriusChat, which seemed to resolve the asker's problem, but they didn't specify any error codes, and the repair cost of 3k is roughly half my entire bank account, so so I wanted to see if I could get any extra feedback.

    Thank you!
     
  2. rjparker

    rjparker Senior Member

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    There is little doubt you need the brake actuator. C1391 Is one of the codes. Obviously a final diagnosis should be made, most likely the dealer will say change it. I would find an independent hybrid shop to install and test. Probably half to two thirds the price. Less if you can do it. I would change both parts.
     

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    #2 rjparker, Sep 16, 2021
    Last edited: Sep 16, 2021
  3. ChapmanF

    ChapmanF Senior Member

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    In a Gen 3, they've got the works split up into two different assemblies:

    [​IMG]

    The one on top is also called the actuator, and the one on the bottom can be called (as shown) the accumulator.

    The one on the bottom pumps up and holds the pressure, but the leak that is bleeding it out can be in either one. (There are more opportunities in the actuator, but that's not a slam dunk.)

    In a way, with your two-second pump cycle time you have an advantage: with a leak that fast, you can probably hear it.

    If you get a mechanic's stethoscope and touch it to each of those two items, during those two seconds between pump runs, one of them is probably making a heck of a hissing sound.

    That'll be the one.
     
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  4. budgrantrules

    budgrantrules New Member

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    I have the same problem (C1391) on my 2010. I've done the paperclip reset thing and it clears the HUD warnings and the breaks work and the battery charges when brakes are applied, but only for about twenty miles. The car is running fine, but not sure how safe it is to keep doing that reset thing. I'm sure I'll need to replace the actuator and/or accumulator and I know that will cost a good bit.
     
  5. ChapmanF

    ChapmanF Senior Member

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    The car isn't fine, and by resetting the codes telling you it isn't, you're not fixing it. The real questions remaining are which of the components need replacement (or both), and who will be doing the work, which will influence the cost.
     
  6. budgrantrules

    budgrantrules New Member

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    Thanks for the quick reply. I realize it isn't fine, but just wanted to know if I was in danger driving it like that. I have a second vehicle (truck that gets <20 mpg so I hate driving it ... only for truck stuff). I made a video of the noises it makes after I turn it off and a brief description. I posted it on YouTube and will add a link once it finishes processing. I have the money for the repairs it is just that I'm a cheapskate :)
     
  7. budgrantrules

    budgrantrules New Member

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    Here is a link to the engine sound in case it helps isolate the issue. I see I can't post a link so copy/paste the below. Thanks

     
  8. ChapmanF

    ChapmanF Senior Member

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    There's no particular need to further isolate the issue. That's the sound of your brake accumulator pump having to repeatedly run because the brake pressure won't hold, which is what the C1391 already was telling you. Having to run every 7 or 8 seconds like that with nobody using the brakes is bad. When your brakes work right, the pressure can hold up for hours if the brakes aren't being used.

    As you've noticed, the brakes still kinda "work" with you clearing the trouble codes, and that'll keep being true until it isn't, and that'll be a different kettle of fish.

    Perhaps the largest potential cost involved is that if the brakes end up surprising you in the wrong way, the other guy's personal injury lawyer will eat you alive if it comes out you've been repeatedly clearing your brake codes.
     
  9. rjparker

    rjparker Senior Member

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    The damage to fix the brake booster is usually $2500 at a dealer.

    Maybe half if you find somebody who will install used parts. Which is not advised because of issues getting the right parts and the extensive labor to change, calibrate and bleed them.

    If you have to pay to do it twice because of a bad used part you could have bought new. New is the thing to do when you are talking brake by wire master cylinders.

    You are already in the failsafe reduced braking mode. Its dangerous. If you are considering selling it, now would be a good time. The low coolants are worrisome as well.
     
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