Brake Actuator Assembly Noise (constant)

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by mpg9999, May 23, 2014.

  1. mpg9999

    mpg9999 Junior Member

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    My wife's prius is making the noise it usually makes after the brakes are pressed (a faint buzz/vibration from the engine), but now it's doing it constantly. It happens every 10 seconds or so for a duration of a few seconds. It also continues to make the sound intermittently after the engine has been turned off. It's also sometimes making a louder noise at the same time, but this one sounds like it's coming from the back of the car. I believe both noises are being caused by the brake actuator assembly. I have a few questions:

    1. Would you all agree this is the brake actuator assembly?
    2. Is it safe to drive? What happens if it fails?
    3. How long do I have until it fails?
     
  2. bisco

    bisco cookie crumbler

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    how many miles on her?
     
  3. mpg9999

    mpg9999 Junior Member

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    About 105k.
     
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Yes
    2. Well, its probably safe for short trips right now, until the problem gets worse. When the actuator fails then the brake system will be significantly impaired.
    3. Unknown
     
  5. edthefox5

    edthefox5 Senior Member

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  6. mpg9999

    mpg9999 Junior Member

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    How significantly impaired?

    FYI I have no warning lights on the dash and my generic OBD scanner shows no codes.
     
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    When you press on the brake pedal, very little will happen and you'll think you are going to hit something or someone.

    To get ready for the failure, I suggest you order Mini VCI now because that will allow you to read the DTC, install a used actuator assembly yourself and bleed the brake hydraulic system (assuming you wish to DIY.)
     
  8. edthefox5

    edthefox5 Senior Member

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  9. mpg9999

    mpg9999 Junior Member

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    Thanks for the advice. Sounds like I should change it now. Where can one purchase a Mini VCI? I've never heard of it before, but I did some searching on the forum and people mention it requiring some kind of software? Can someone clarify what I will need? This is unrelated to my original question, but will a Mini VCI also help me bleed the engine coolant? She is past 100k and it's due.
     
  10. nh7o

    nh7o Off grid since 1980

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    The mini VCI installs on a laptop, preferably an old XP unit that is not used on line. Get it from eBay or Amazon or other places. About $30. It is needed to bleed the brakes properly on the Prius. There is no need for it to change engine coolant, and the instructions are on PriusChat.

    If the brake actuator does fail, it is a pretty big job to change it, but has been done by DIY'ers successfully. You could get a used unit fairly easily.
     
  11. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Mini VCI will also work with a Windows 7, 32 bit OS laptop.

    Regarding the engine coolant change, the Mini VCI can run the CHRS pump instead of shorting the CHRS relay contacts which was the workaround I had devised prior to Toyota Techstream becoming easily available via Mini VCI.
     
  12. mpg9999

    mpg9999 Junior Member

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    Update:

    The Prius was due in for the steering shaft recall so I had the dealer take a look at this issue as well. After paying for an hour of diagnostics they said they think its the skid control ECU, which is just as expensive as the brake actuator. They pulled the following code: C1378. They told me its another 3 hours of diagnostics to make sure it is in fact the ECU, which would apply towards the labor of changing it if it is bad. Where is the skid control ecu located? I don't want to spend 2k on this ECU just to have the actuator still making this noise and then have to spend another 2k on that. Any suggestions?
     
  13. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The skid control ECU is located near the steering shaft and that is probably harder to get to than the brake actuator because much of the instrument panel including the steering wheel and driver's airbag have to be removed for access.

    If you can DIY, look at techinfo.toyota.com to see what is involved in troubleshooting that DTC. An oscilloscope is needed to seriously perform the troubleshooting process. If you cannot DIY then you will be at the mercy of your dealer's service dept.
     
  14. nh7o

    nh7o Off grid since 1980

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    mpg9999, where are you located? There might be better help in your area than the dealer. You might ask them if installing a used part would be acceptable.
     
  15. nh7o

    nh7o Off grid since 1980

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    Manual: C1378 Capacitor Communication Malfunction:

    DESCRIPTION
    The brake control power supply assembly (capacitor) provides auxiliary power for brake control when an
    auxiliary battery (12 V) voltage drops.

    The FAIL and ENA line are placed between the skid control ECU and the brake control power supply
    assembly. Signals indicating that the brake control power supply is in auxiliary mode are sent to the skid
    control ECU through the FAIL line.

    Charge permit prohibition signals are sent to the brake control power supply through the ENA line.
    ----
    This is about the 12V power supply for the brakes, located next to the 12V aux battery in the back, not being detected properly by the brake ECU. However, this is one of the areas where DTC's are sometimes seen when the 12V battery is in marginal condition and the voltage drops low enough at start up. So before anything else, be certain that the 12V battery is good. The manual lists the brake ECU or the wire harness as the problem areas, but this an additional one.

    As for the unusual running of the actuator, I would say based on reports seen here on PC, the actuator has normally been the problem. It should be possible to check things sufficiently to determine which system is at fault without using a shotgun approach. It requires detailed schematic level probing to do this.
     
  16. mpg9999

    mpg9999 Junior Member

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    Is techinfo.toyota.com a pay site? It looks like I need a subscription. The dealership mentioned using an oscilloscope as part of the further troubleshooting. I don't own one of my own.

    The Hampton Roads area of Virginia. I'm not aware of any Interdependent Hybrid Experts in the area.


    Yeah, I am a little bit concerned about this. Lets assume for a moment that the 12v battery, or some other issue unrelated to the brake actuator is causing C1378 to appear. Lets also assume that the noise I'm hearing is in fact caused by a bad brake actuator. If they follow the diagnostics called for by C1378, will their troubleshooting still lead them to believe I have a bad skid control ECU? I'm just very concerned that the skid control ECU could be misdiagnosed, leaving me 2,000 dollars poorer, and still in need of a 2,000 dollar brake actuator.
     
  17. nh7o

    nh7o Off grid since 1980

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    Yes, that is the concern that needs to be considered. the dealer just follows the troubleshooting tree, and if replacing a part does not solve the problem, then they can't take it out and put the old one back in again. They charge you just the same, potentially. Some are better than others, but at worst it is not a very fair way to conduct business.
     
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