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Brake Booster/Accumulator Troubleshooting

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Tusker, Jul 20, 2024 at 11:50 PM.

  1. Tusker

    Tusker New Member

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    2013 Prius
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    Hi All,
    I just finished putting an engine in a 2011 Prius I bought with a blown engine. First startup was this afternoon and I quickly realized that the brake accumulator is running much more frequently than my other Gen 3's. When the car is turned on initially, it will begin cycling every 7 seconds or so, gradually increasing to about 20 second intervals over the course of about 10 minutes. I can hear an audible hissing sound in the brake accumulator/master cylinder area, but I can't determine exactly where it is coming from. The fluid level will drop about 1/8" every time it cycles and will slowly fill back to the original level before the accumulator cycles again.

    I cleared the codes a number of times after the first startup to deal with some of the issues caused by the batteries, etc being unplugged or inactive. There was a brake code present at one time, but I can't remember exactly what it was (1391, maybe?). Whatever code might have been there, it isn't coming back. There are still no codes showing after about a 10 mile drive.

    With no codes present, I'm tempted to just leave it, but I know the frequent cycling and leaking sound isn't normal and I'd like to take care of this while I'm still getting this car ready for the road. A few questions:

    1. I've read that some leak down of the accumulator is "acceptable". What is the generally acceptable frequency for accumulator cycling?
    2. Based on what I described above, is it more likely that the leak is in the brake master or the accumulator?
    3. Can anyone help by pointing me to some previous posts that break down the troubleshooting method for how to determine if its the brake master or accumulator?

    Thanks in advance
     
    #1 Tusker, Jul 20, 2024 at 11:50 PM
  2. ChapmanF

    ChapmanF Senior Member

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    IV
    The pressure normally holds a long time if you're not using the brakes. If I'm sitting parked with the car in READY, I generally won't notice the brake pump any more often than the engine cycles while parked (the car applies the brakes when it's about to start or stop the engine while parked, for less of a jolt in the car, and as with any use of the brakes, a few of those will cause the pump to run again). Seven seconds is nowhere near normal. Audible hissing is nowhere near normal.

    A mechanics' stethoscope is very cheap, but if you don't have one, even a long screwdriver or stick pressed below your ear can be very helpful in localizing a noise.

    Ideally, you could determine which of these two is where you hear the hiss most prominently:

    [​IMG]

    If you can't, then just playing the odds, the odds favor the top one. It has many more valves in it to go bad.
     
    #2 ChapmanF, Jul 21, 2024 at 12:14 AM
  3. Tusker

    Tusker New Member

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    Vehicle:
    2013 Prius
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    Two
    I have a parts car, so just decided to change both while I had things apart. Not the worst job in the world. 2 hours including pulling the parts from the donor car.

    Now I just need to figure out how to get this system bled. I don't have tech stream and the brake bleed function on my scanner isn't compatible with this car. Is there a way to do this manually?
     
    #3 Tusker, Jul 21, 2024 at 1:50 PM
  4. ChapmanF

    ChapmanF Senior Member

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    IV
    No. Not after that kind of work at the head end.

    We do have a gen 2 thread reviewing scan tools, which seems to have identified a couple good choices with the right capabilities. While it isn't specific to gen 3 (nobody has sent mr_guy_mann a gen 3 to test on), it might be a start.

    Gen2 OBD2 app review | PriusChat
     
    #4 ChapmanF, Jul 21, 2024 at 2:13 PM
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