Gen 2 C1256 low accumulator pressure -- help verify part numbers for fix?

Discussion in 'Gen 2 Prius Main Forum' started by Horseflesh, May 2, 2025 at 7:13 PM.

  1. Horseflesh

    Horseflesh New Member

    Joined:
    Mar 2, 2025
    15
    5
    0
    Location:
    Pacific Northwest
    Vehicle:
    2008 Prius
    Model:
    N/A
    My 2008 Prius has code C1256 and the pump runs about every 10 seconds... No ABS or Check Engine light yet, though.

    I have a friendly Toyota mechanic who will do the work for a good price for me, and get me dealer pricing on the parts... but he wants part numbers so we can get them on the way.

    The shop is far away and the hasn't been formally diagnosed, but... Assuming I have the classic C1256 problem I believe the best practice is to replace the "master cylinder" and the "actuator assembly," correct? Can someone help me verify the correct part numbers for a 2008 Gen 2?

    This is what I have so far.

    Master cylinder assembly 47200-47020
    https://parts.olathetoyota.com/oem-parts/toyota-master-cylinder-assembly-4720047020

    Actuator assembly -- I see references to THREE parts!

    Original version: 44500-47141 -- Not what you want, it was redesigned.

    Newer version: 04003-44647 -- The replacement part per this bulletin. I assume this is what I want.

    Even newer version? 44510-47051 -- I have seen this discussed on forums but it is unclear if this applies to a 2008 Gen 2. OEM parts sites don't even have anything under this number!
     
    #1 Horseflesh, May 2, 2025 at 7:13 PM
  2. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    25,974
    16,951
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    In gen 2 I have not heard of much need to replace the master cylinder. The gen 2 M/C is conventional and very simple. Nearly all the interesting stuff is glommed together into the actuator assembly. (The stroke simulator is off someplace else, but I don't hear much about that needing attention either.)
     
    #2 ChapmanF, May 2, 2025 at 7:19 PM
  3. Horseflesh

    Horseflesh New Member

    Joined:
    Mar 2, 2025
    15
    5
    0
    Location:
    Pacific Northwest
    Vehicle:
    2008 Prius
    Model:
    N/A
    I've read many times 'round here and other places that it is "best practice" to replace both, though I've not yet seen an EXPLANATION for that. If it's one of those things were you might as well since you've sunk labor cost I'm still OK with it.

    Google's AI search "helper" says that it's best to do both, as it is possible for the failing accumulator to damage the master cylinder, but for all I know that is a hallucination!

    For the actuator ... Is -44647 the way to go or do I need to find the un-orderable-new -47051 ?
     
    #3 Horseflesh, May 2, 2025 at 7:29 PM
  4. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    25,974
    16,951
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    You've quite possibly read a lot that was about gen 3. In gen 3 the master cylinder and the actuator and the booster and the brake ECU are a single assembly, while the booster pump (note that 'booster' and 'booster pump' are different things) and accumulator make up a different assembly, and both of those two assemblies can contribute when pressure isn't being held.

    But if you're talking about a gen 2, the booster pump and accumulator and actuator are all combined in one assembly that is pretty much where most of what can go wrong is, and the master cylinder in gen 2 is a dead-simple conventional one—lacking even a booster—more like you'd find on a car of the '60s.

    I'm not at all surprised that an AI would come up with some cockamamie result, given the number of significant differences between Prius generations that it would hardly know to keep apart in all the internet text it has ingested.
     
    #4 ChapmanF, May 2, 2025 at 8:31 PM
    Horseflesh likes this.
  5. Horseflesh

    Horseflesh New Member

    Joined:
    Mar 2, 2025
    15
    5
    0
    Location:
    Pacific Northwest
    Vehicle:
    2008 Prius
    Model:
    N/A
    Thanks, that's very helpful!
     
    #5 Horseflesh, May 2, 2025 at 8:39 PM
(You must log in or sign up to post here.)