Need info on fixing leaking accumulator

Discussion in 'Gen 3 Prius Main Forum' started by Jim Caldwell, Oct 11, 2021.

  1. Jim Caldwell

    Jim Caldwell Member

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    The car is a 2014 Prius. The only DTC is code C1391. I have Techstream. The anti skid and brake lights are on intermittently. There are only 2 Toyota dealerships that will work on car. There was special coverage for defective accumulator on these cars, but they said that I was 4000 miles past the special warranty. I have only a gen III wiring diagram and a Bentley Gen II manual. I know these dealerships are going to charge 1500.00. to 2000.00 or more. I dont have that much now. I am a pretty good mechanic. The Bently gives a block diagram and description of the braking/ antiskid system. Is there any tech pub i can buy that goes into some detail on troubleshooting this system? How much does factory service manual cost and could I even get one?
    The car makes a motor whirring sound when drivers door is opened. I think this might be the accumulator pump?
    For all I know, it could be a bad accumulator pressure sensor or connection to it. But the dealerships of course will sell me 1000.00 worth of parts no matter what the real fix is. The first thing I want to try is checking press sensor connector. If that doesnt fix it, then replace the sensor. Its bound to be lots cheaper than the accumulator or motor. But I cant do anything since i dont know where these thee parts are located. Anyone know?
     
  2. TMR-JWAP

    TMR-JWAP Senior Member

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  3. PriusCamper

    PriusCamper Senior Member

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    I find it curious the way we're slowly transitioning from Gen2 to Gen3 work... I now have an opportunity to do my first head gasket and am still trying to decide if I really want to go down that rabbit hole?
     
  4. TMR-JWAP

    TMR-JWAP Senior Member

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    I still have a prime condition 2008 in the driveway that needs the abs assembly replaced and I'm not sure if I want that rabbit hole either. I even have 6 of the assemblies on the shelf ready to try. Just haven't made the time, and not 100% certain I want to. For being in a pandemic, life sure has been exceptionally busy............
     
  5. PriusCamper

    PriusCamper Senior Member

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    yea... it's all about the bubbles... As in getting bubbles out of the cooling system or the braking system... Avoiding those hassles make Prius repair work fun! :) Of course once we get good gear gear and technique by facing the challenge we'll likely wonder why we avoided it for so long?
     
  6. Mendel Leisk

    Mendel Leisk Underfoot

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    Attached is a service bulletin regarding Brake Booster Pump Assy replacement, and I'll pm you a Repair Manual link.
     
  7. ChapmanF

    ChapmanF Senior Member

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    One thing about that pdf, on page 20 they show a torque (31 inch pounds) for tightening the two nuts, and they were able to calculate that torque because they know the length of the specific torque wrench they tell you to use, and the length of the custom "brake pump wrench" extending it.

    From the picture, they look about equal, so that's probably about 62 inch pounds at the nuts. If you're using your own improvised tools, the math may be different.
     
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  8. rjparker

    rjparker Tu Humilde Sirviente

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    There is no easy or cheap solution when the pump accumulator won't build pressure fast enough. It needs to be changed. It is a very common problem.

    Some might risk a used pump but since this is brake by wire and essential, most spend the money for new parts. A metal diaphragm in the unit leaks, usually taking out the abs/brake ecu/master cylinder in the process.

    Even if you replace both units, the brake stroke simulator portion has to be calibrated and a special flushing technique is required, both using Techstream.

    There are various versions of the master cylinder making a used option more difficult. Used sellers generally don't know this so it would be prudent to have the donor vin for part compatibility verification. The Toyota part number is not on the master cylinder.

    I would appeal to Toyota Corporate for a repair even though you must be over 150,000 miles.

    This recent video details the replacements short of the Techstream process.

     
  9. Mendel Leisk

    Mendel Leisk Underfoot

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    There's also something tricky with the pump unit, there was a revision to it, and (IIRC) rather than revise the part number, they just rotated the label on one of the "beer cans", through 90 degrees. Or maybe they did revise part no too?
     
  10. TMR-JWAP

    TMR-JWAP Senior Member

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    Another inexpensive option is to refresh the brake fluid. I've experience some significant improvements in the pump run times after replacing the brake fluid. It's a relatively inexpensive thing to try.
     
  11. ChapmanF

    ChapmanF Senior Member

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    Sometimes a part of the problem is nitrogen leaking out of the accumulator. If it does, it gets into the brake fluid, and there are two problems:

    1. There is less nitrogen in the accumulator, so it goes from max to min pressure faster, and the pump has to run more often. (This is just like a house on well water when there is not enough air in the pressure tank.)
    2. There are nitrogen bubbles in the brake fluid. Every time you brake, they have to be compressed, which takes extra fluid. When you release, they re-expand and blow the extra fluid back to the reservoir. This means more fluid is used for each use of the brakes, and the pump has to run more often.

    Both 1 and 2 contribute to the frequent pump runs. When you do a fluid replacement (or just go through the actuator bleed sequence, which requires some new fluid but not as much as full replacement), you can get the bubbles out of the fluid, which fixes 2. Nothing you do puts the nitrogen back in the accumulator, so the 1 part will keep steadily getting worse (and eventually giving you the 2 part again, probably sooner than the last time). But at least dealing with the 2 part gives a noticeable improvement that can last for a while.
     
  12. TMR-JWAP

    TMR-JWAP Senior Member

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    Fortunately, the accumulator on a Gen 2 can be replaced independently from the actuator assembly just by unthreading it from the valve body block. I think it's a 15 or 17 mm hex on the end of the accumulator. You just need to discharge the accumulator to the reservoir via techstream to bleed all pressure from the brake system prior to loosening. Not sure if it's possible on the Gen 3. Pretty sure the accumulator can be unthreaded, just not sure if there's adequate room to do it.
     
  13. rjparker

    rjparker Tu Humilde Sirviente

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    Flushing the fluid will fix it for about a day. Been there done that. The gen3 has a separate pump accumulator.
     
  14. Mendel Leisk

    Mendel Leisk Underfoot

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    Attached are the non-Techstream and Techstream brake bleed methods, from Repair Manual. @ChapmanF has noted in past that the Techstream method may be required if there's anomolies in the firewall gizmos.

    To clarify a very obtuse bit of the non-Techstream instruction, the order they say to bleed is F/R, F/L, R/L and finally R/R.
     
  15. ChapmanF

    ChapmanF Senior Member

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    It's always worth a reminder that those sections of the manual are not brake bleed instructions.

    They are brake fluid replacement instructions. In fluid replacement, you start with a system full of fluid, no air, no need for bleeding. You let old fluid out and new fluid in, no air, no need for bleeding. These instructions will work for that.

    If there is air but it is only in the wheel cylinder lines or calipers, you can also get away with these instructions. If there's air in the head end, you can't, and have to bleed with Techstream. Techstream will walk you through doing the fronts two times, two different ways, to bleed the two different circuits; no non-Techstream procedure is provided for that.

    If you are doing a simple fluid replacement and take your eye off the reservoir and get air in, you will also need to bleed the head end, and will need Techstream to do it.
     
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