Brake System Issues (ABS, BRAKE, VSC)

Discussion in 'Gen 2 Prius Technical Discussion' started by RadarWatch, Nov 8, 2021.

  1. RadarWatch

    RadarWatch New Member

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    To start: recently my Gen 2 prius has had some reduced pressure when initially starting the car and shifting into reverse. Almost as if the accumulator pump was not running as it should on door open.

    Then a week or two later, I would notice the BRAKE, ((!)), ABS, VSC lights would not turn off until the pedal was released during start up. So the vehicle would be powered to ready, lights stay illuminated until I released my foot and then they turned off.

    Now a week later, my BRAKE, ((!)), ABS, VSC stay on, with reduced braking force. I have attempted the OBD II 4 / 13 pin reset and blink out and found codes:

    BRAKE 36 57 66
    ABS 42 95
    VSC 43 45 62 63

    BRAKE 36 - Foreign Object is Attached on Tip of Front Speed Sensor LH
    - Left front speed sensor
    - Speed sensor circuit
    - Sensor installation

    BRAKE 57 - Accumulator Low Pressure
    - Brake actuator assembly (accumulator pressure, accumulator pressure sensor, pump motor)

    BRAKE 66 - Linear Solenoid Valve Offset Learning Undone
    - Initialization of linear solenoid valve and calibration undone

    ABS 42 - Open in IG1 / IG2 Power Source Circuit
    - ABS NO. 1 relay
    - ABS NO. 2 relay
    - Harness and connector
    - Skid control power supply circuit
    - Brake control power supply assembly
    - Hybrid control system

    ABS 95 - ECM Communication Circuit Malfunction
    - Skid control ECU

    VSC 43 - Acceleration Sensor Stuck Malfunction
    - Yaw rate (deceleration) sensor
    - Skid control ECU

    VSC 45 - Acceleration Sensor Output Malfunction
    - Yaw rate (deceleration) sensor
    - Zero point calibration not done
    - Skid control ECU

    VSC 62 - Front Hydraulic System RH Malfunction
    - Fluid leakage
    - Brake actuator assembly
    - Disc rotor

    VSC 63 - Front Hydraulic System LH Malfunction
    - Fluid leakage
    - Brake actuator assembly
    - Disc rotor

    I checked brake fluid level all is normal, battery is new (replaced in last 12 months) no sign of parasitic drain. The accumulator pump can still be heard, albeit not as often.

    These codes make me want to assume my Skid Control ECU has died, thoughts? Thanks for any help!
     
  2. SFO

    SFO Senior Member

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    Welcome to PriusChat!!

    Generally speaking, if there are warning lights on the dash, then you have OBD2 codes (DTCs) stored in the ECUs (computers). Find the various parts stores for free scans (each scanner may not be hybrid compatible), then post the codes here for additional guidance. You might be able to find a nice mechanic with a hybrid scanner that will scan it for free as well, it only takes a couple of minutes at most.

    You or a mechanic may need a mini-vci cable and techstream on a windows device (or emulated) to sort out the mentioned codes, ie Linear Offset Learning. Do you have a DIY attitude and some tools to fix the problem(s), or will you be relying on someone else for help?

    Texas is a fairly larger state, which metroplex are you near, as another member may be able to offer help.

    FYI : you're moderated until you've posted 5 times.
     
  3. RadarWatch

    RadarWatch New Member

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    I've tried my android OBDII cheap-o reader and Autozones reader with no codes. (why I translated the blink codes).

    I'm pretty DIY, I do all the work for family's vehicles, but the prius braking system is a bit complex and I am hesitant to drop cash on a Techsteam. I did read there might be some electronic configuration regarding replacing ECU, accumulator, or other sensors.

    and I am located in the DFW metroplex. Some other information: 2004 Prius with 181k miles, original brakes.
     
  4. dolj

    dolj Senior Member

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    You are confusing ABS 42 with ECB 42. The above should be:

    ECB 42 - Open in IG1 / IG2 Power Source Circuit
    - ABS NO. 1 relay
    - ABS NO. 2 relay
    - Harness and connector
    - Skid control power supply circuit
    - Brake control power supply assembly
    - Hybrid control system

    ABS 42 is undocumented in a lot of the hard copy versions that are around and it simply means "hey, you have codes on the Brake Control Warning Light (ECB codes) - ((!)) -, go look there."

    I notice you do not include any codes blinked by the ((!)) light.
     
    #4 dolj, Nov 9, 2021
    Last edited: Nov 9, 2021
  5. RadarWatch

    RadarWatch New Member

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    All the codes prefixed by BRAKE are the ((!)) blink out. Thanks for the information about ABS vs ECB. I can upload a video of my codes if someone would like to crosscheck them.
     
  6. SFO

    SFO Senior Member

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    Each chain, and each individual store will likely have different OBD2 scanners in use, you should hit them all up (O'reilly, AAP, CarQuest, NAPA, etc). Which App are you currently using, and have you tried Torque, Dr Prius, or Hybrid Assistant with your android OBD2 adapter?
    Buying a mini-vci cable (or better) for $20+ might be prudent, as techstream offers the same diagnostic/repair abilities as a dealer tech.
    Maybe one of the guys at @Texas Hybrid Batteries can do a quick scan for you : https://texashybridbatteries.com/
     
  7. RadarWatch

    RadarWatch New Member

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    Yeah I can try a few more chains. I use Torque, I have not tried Dr. Prius app yet.

    In regards to the mini-vci, I did not realize the software / connector combo was so cheap. I've read that v8-10 is best for this generation and that it might have to run on Win7.

    In the meantime I've ordered a used Skid Controller ECU.
     
  8. SFO

    SFO Senior Member

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    Might try another App, or it could be the adapter. Is it mentioned here : Hybrid battery diagnostic and repair tool for Toyota and Lexus

    Did you install or use the gen2 PIDs in Torque?
    The version shouldn't matter, and for brake actuator work, more recent may be better. Many winblows (xp+) will work, even emulated.
    Seems a bit early to be throwing parts at it, have you been through the various workups step by step?
     
    #8 SFO, Nov 11, 2021
    Last edited: Nov 11, 2021
  9. RadarWatch

    RadarWatch New Member

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    Techstream arrived:

    Code:
    C1256 - Accumulator Low Pressure
    C1300 - ABS ECU Malfunction
    C1344 - Hydraulic System (RL)
    U0123 - Lost Communication with Yaw Rate Sensor Module
    U0124 - Lost Communication with Lateral Acceleration Sensor Module
    U0126 - Lost Communication with Steering Angle Sensor Module
    Obviously C1256 is the biggy. After looking at the trigger conditions it aligns with my previous experience. Low pressure at start up, while I rapidly shift into reverse and provide speed input. I got in, in a hurry, started to ready and shifted to reverse felt lack of pressure and triggered code.

    Why was there low pressure? Not sure, it's my understanding the accumulator builds pressure on door open, maybe I didn't provide it enough time or it's on the way out.

    I cleared the codes and drove it around the neighborhood, and for good measure calibrated the sensors on level ground in accordance with repair manual. We'll see if it returns. I would like a second trigger before replacing the pump to reduce the odds of it being a fluke event.
     
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  10. mr_guy_mann

    mr_guy_mann Senior Member

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    You have Techstream, so why not monitor and record data from the ABS ecu? Work the brake pedal and see what pressure does the pump kick in. What pressure does it turn off? How long does it take to build pressure? How long can it just sit there before the pump turns on again. Try running those tests in Ready (at 14V) vs ignition on but not Ready (at whatever voltage the 12V battery can hold).

    Posted via the PriusChat mobile app.
     
  11. RadarWatch

    RadarWatch New Member

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    Well the codes came back and there is an audible difference in accumulator sound. It sounds weaker now so definitely a failing accumulator, just ordered a refurbished one.
     
  12. alftoy

    alftoy Active Member

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    Which MINI VCI J2534 Cable did you order? May be of help to others that are contemplating a Techstream cable.
     
  13. koco

    koco Member

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    Where did you find a refurbished accumulator? I have looked for info on how they can be refurbished and couldn't find anything except for someone dismantling one on Youtube.
     
  14. RadarWatch

    RadarWatch New Member

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    I bought a $100 VXDIAG software came provided.

    Turns out it wasn't refurbished just pulled from a yard. Was caked in crud. Installed it the other day but am having some unusual behavior. I bled the system multiple times and it seems like there's an unlimited supply of air. (possibly a leak or loose connection)

    The brakes seem to apply unevenly (similar feel to a warped rotor rapid on/off), pump makes unusual sounds. Still investigating what I did wrong.
     
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  15. RadarWatch

    RadarWatch New Member

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    So replaced actuator pump.. Bled that night and for good measure as I wanted to be sure all the air was out of the system bled again in the morning.

    Now sometimes the pump is audibly louder than other times. It runs almost non-stop and got some new codes:

    Code:
    C1253-136 - Hydro Booster Pump Relay
    C1256-143 - Accumulator Low Pressure
    C1391 - Abnormal Leak of Accumulator pressure
    
    I can't see any leaks.. But that's my first inclination was there's a leak and air is entering the system somewhere. After driving it 80 miles or so the brakes have not faded, I feel like if there was a leak we would have lost all pressure by now..

    The brake application does feel different, pedal feels different at times and at low speeds the application doesn't feel all that smooth. On the first day it felt almost like warped rotors however that feeling isn't as present anymore.

    What should I do? Another bleed? Relay test? How much fluid does it normally take to completely remove all air from the system after accumulator replacement?
     
  16. ChapmanF

    ChapmanF Senior Member

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    While external leaks are not unheard of, the usual scenario is an internal leak. Some valve in the actuator doesn't seal perfectly, and fluid constantly trickles past it and returns into the reservoir, so the accumulator pressure doesn't hold up, and the pump has to continually run to pump it back up.

    Of course with an internal leak there isn't anything to see. No fluid ever leaves the system. Depending on how fast it is, a stethoscope might pick up a hissing sound.
     
  17. RadarWatch

    RadarWatch New Member

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    So if it's an internal leak then the used accumulator I got is bad. What if I moved the motor from my used one to my old one that died?

    In addition my prius makes loud buzzing when stopped if this is any indication of anything. Here's a video:

     
  18. ChapmanF

    ChapmanF Senior Member

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    A few times you've said you replaced the "accumulator" or replaced the "actuator pump", but if this is a Gen 2 we're talking about, Toyota doesn't sell the accumulator or the pump separately; they just sell the brake actuator assembly (44510 here), the whole enchilada that also includes those parts.

    [​IMG]

    Did you replace the whole enchilada at some point in this story, or have you really been somewhere obtaining bits and pieces of it and changing those?
     
  19. RadarWatch

    RadarWatch New Member

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    My bad mixing up words.. Yes, Ive replaced the actuator pump with a used pump online. Now I'm trying to debug either a faulty replacement pump or an installation issue.
     
  20. ChapmanF

    ChapmanF Senior Member

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    The whole actuator assembly, right? Big square box with lots of brake lines and two big round things sticking off it. Not just the pump (the pump is one of those round things, not sold separately by Toyota).
     
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