ABS Actuator Master Cylinder Assembly Replacement Problem

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by SilverWagon, Apr 13, 2026 at 4:11 AM.

  1. SilverWagon

    SilverWagon Junior Member

    Joined:
    Nov 7, 2023
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    Location:
    San Diego
    Vehicle:
    2012 Prius c
    Model:
    Three
    I purchased a 2013 Prius C recently with a known Braking System issue. When I purchased the car I could hear some light hissing coming from under the driver side dash and the booster kept regenerating every 15 minutes. The car was priced for the problem so I purchased it.

    I thought to start with buying a used Master Cylinder Assembly from the junkyard but first I went to Toyota to get a part number. Toyota said my VIN needed the 47050-52040 because the car came with 16" wheels. The only used MCA I could find was a 47050-52020, which is for 15" wheels. I was going to change the wheels to 15s anyways because they have a better ride and longer life, so I purchased it assuming I could program it for use.

    I removed the original MCA and installed the used 47050-52020. The every 15 second ABS pump sound is now gone but my Xtool D8S scanner gave me two codes C1203 Communication Circuit of ECM and C1345 Linear Solenoid Value Offset Learning Value Undone.

    I started by clearing or resetting the calibration memory for the new MCA. Then Google Gemini said to select ECU Replacement or ECU Communication Reset in the Xtools scanner. I wasn't able to find this in the menu so I went on to the next step (Fix C1345 (Linear Valve Offset Learning). The scanner bled each wheels brakes but the front right didn't behave like the others. When depressing the brake pedal and holding it down, the other wheels brake bleeders would continuously push out brake fluid. The FR bleeder would only push out brake fluid if the brake pedal was pumped.

    Then, in the last part of the of the Linear Valve Offset Learning was the Stroke Simulator. I hooked up a tube to the bleeder on the MCA, opened it up, and ran the program. I could hear the MCA making noise but no brake fluid came out.

    At this point I'm assuming the used MCA I purchased is either bad or doesn't work with my car. I can't get those codes cleared and the issues with bleeding the MCA has me concerned.

    Any thoughts?
     
    #1 SilverWagon, Apr 13, 2026 at 4:11 AM
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

    Joined:
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    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    I cannot claim with certainty that your new brake module is being electronically rejected by the other ECUs in the car... but that is a thing that happens with brake modules in other Priuseses. The other modules know what they should be communicating with and they won't play until you provide exactly the right hardware.

    Unfortunately the 16" wheel option was a very rare one, so it isn't going to be easy to find a secondhand module that matches.

    I would try car-part.com, which is a searchable database of auto recyclers.

    Good luck!
     
    #2 Leadfoot J. McCoalroller, Apr 13, 2026 at 11:05 AM
  3. ChapmanF

    ChapmanF Senior Member

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    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    The front behavior doesn't sound strange to me. There are independent fluid passages serving the front brakes. The full bleed procedure has you go to both front brakes twice. One time you are bleeding the fail-safe passages that only work with pedal pumping. The other time you are bleeding the ops-normal passages supplied by the pump and accumulator.

    The part that does seem weird to me is that you only noticed it on the front right.

    I'm not sure about the stroke simulator. I might have seen a similar story in another thread, but I don't remember how it turned out.

    The C1203 is a weird code. It technically means the brake ECU isn't convinced it's in the right car. But there's also a "HINT" in the RM saying the code will be present in any case before the linear solenoid offset has been learned. So, when you have the code together with a C1345, it makes perfect sense to not panic, and go through the offset learning and see what happens. But if you still have the C1203, it will probably mean the ECU had checked with the other ECUs in the car and decided it's the wrong calibration for your original wheel size.
     
    #3 ChapmanF, Apr 13, 2026 at 11:27 AM
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