ABS Brake Acumulator

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ti_vakabon, Nov 26, 2020.

  1. ti_vakabon

    ti_vakabon New Member

    Joined:
    Nov 26, 2020
    3
    0
    0
    Location:
    Florida
    Vehicle:
    2008 Prius
    Model:
    Base
    2008 Toyota Prius. ODO 172k miles. ABS failure. C1252 - Hydro-boost motor malfunction & C1256 - Acumulator low pressure malfunction. From what I understand, upon depressing the brake pedal, the Skid Control ECU (SC ECU) uses input from the master cylinder and brake pedal stroke sensor to calculate the desired target hydraulic line pressure (THLP) for each wheel. Actual hydraulic line pressure (AHLP) is then compared to the target hydraulic line pressure. If the AHLP is too low, the SC ECU opens solenoid valves to feed fluid pressure from the accumulator to the wheels. When the AHLP at each wheel equals the THLP, the SC ECU closes all solenoid valves to hold and maintain hydraulic line pressure at each corresponding wheel. I have deduced that the pump motor "on time" is abnormally long which means it is either not building pressure or it isn't holding pressure thus the malfunction. Attempting to locate source of issue. Any input is much appreciated. Thanks
     
  2. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    14,203
    10,046
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    For starters, do you hear the pump running? Sometimes there can be an electrical issue where the ECU tries to run the pump but the pump doesn't run, or runs very feebly, and of course that leads to a long "ON" time (at least, commanded ON, though it may not really be running) without building the pressure to target.

    Or, you might actually hear the pump running for long periods, which would mean electrically it is getting power and running, but is not building to the proper pressure, either because the pump innards are worn, or because some actuator valve (one of the ones that are supposed to be closed except when relieving pressure) might not be seating fully, and pressure is bleeding past it.

    In a Gen 2 there is only so much value in pinpointing the cause, because the whole actuator assembly including the accumulator and pump is sold as one unit. In the other generations where those parts were split out, there could be more of an incentive to pin down which one to replace.
     
  3. ti_vakabon

    ti_vakabon New Member

    Joined:
    Nov 26, 2020
    3
    0
    0
    Location:
    Florida
    Vehicle:
    2008 Prius
    Model:
    Base
    Thanks for the quick response. I took a long look at the ECU's circuit board, I didn't find any corrosion or broken traces. I did however, re-solder some suspicious looking pins but the issues still persisted afterwards. And from what I've observed, the pump runs, albeit continuously... from start to end of commute. I'm pondering if the ABS can be bypassed... direct line from master cylinder to brake lines? Anyhow, thanks again.
     
  4. mr_guy_mann

    mr_guy_mann Active Member

    Joined:
    Sep 3, 2020
    956
    410
    0
    Location:
    NJ-USA
    Vehicle:
    2006 Prius
    Model:
    Four
    You seem to have solid grasp of the theory of operation. The master cylinder inputs tell the hybrid ecu how fast the driver wants to slow down. The hydrid ecu determines how much regen to do vs hydraulic braking. Really, all that matters is that the actuator assembly has proper power supply and ground. Pretty much everything else is internal to the assembly.

    Posted via the PriusChat mobile app.
     
  5. rjparker

    rjparker Senior Member

    Joined:
    Jun 6, 2008
    3,815
    1,975
    2
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    When the system fails completely it automatically defaults to a bypassed condition. No power brakes and long stopping distances. A common problem is the pump or accumulator is leaking pressure. As Chapman indicated, you likely need a new assembly. That means new from Toyota or used from salvage. Plus installation and bleeding.

    Typical part number (one of several - apparently has been updated many times)
    44500-47141
     
  6. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    14,203
    10,046
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Was some outfit like Cardone offering a reman? Something about that rings a bell for me, but I'm not easily finding it online right now. Maybe I dreamed it.
     
  7. rjparker

    rjparker Senior Member

    Joined:
    Jun 6, 2008
    3,815
    1,975
    2
    Location:
    Texas Hill Country
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
  8. ti_vakabon

    ti_vakabon New Member

    Joined:
    Nov 26, 2020
    3
    0
    0
    Location:
    Florida
    Vehicle:
    2008 Prius
    Model:
    Base
    Attn: ChampmanF, mr_guy_mann, rjparker
    Thank you all for the responses. After much thought, I decided to purchase a remanufactured assembly.
     
Loading...