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

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Horseflesh, May 2, 2025 at 7:13 PM.

  1. Horseflesh

    Horseflesh New Member

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    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

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    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

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    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

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    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
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  5. Horseflesh

    Horseflesh New Member

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    Thanks, that's very helpful!
     
    #5 Horseflesh, May 2, 2025 at 8:39 PM
  6. JC91006

    JC91006 Senior Member

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    #6 JC91006, May 4, 2025 at 10:26 AM
  7. Horseflesh

    Horseflesh New Member

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    Unfortunately the only references this part number I can find are on sites like ebay, for used parts. No OEM shops list 44510-47051. Toyota.com doesn't even know this part number.

    upload_2025-5-4_8-59-42.png

    Someone posted that they got it from Group 1 but they do not have it either. (and their parts search looks suspiciously like the Toyota dealers.)

    Edit to add:

    This may be a case where x051 actually isn't the real part number, @ChapmanF posted about that here.

    ABS actuator part numbers | PriusChat

    OK and another user in that thread called a dealer and confirmed 44500-47141 was the current part number. Then they said:

    So I ordered a brand new 44500-47141. The receipt shows 44500-47141. The Toyota box has 44500-47141 on the label. The part inside is labelled 44510-47051.

    So, I guess I should order 44500-47141.
     
    #7 Horseflesh, May 4, 2025 at 12:07 PM
    Last edited: May 4, 2025 at 12:17 PM
  8. JC91006

    JC91006 Senior Member

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    When you order it from the parts department, it'll be under part 44500-47141. The reason is because this part is sold with a resistor. And because of that, Toyota had to create a part number for you to purchase with the resistor.

    So when you order 44500-47141, it'll come with the actuator part 44510-47051 and the resistor
     
    #8 JC91006, May 4, 2025 at 12:32 PM
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  9. Horseflesh

    Horseflesh New Member

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    Thank you!
     
    #9 Horseflesh, May 4, 2025 at 12:36 PM
  10. JC91006

    JC91006 Senior Member

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    I find it strange you can't buy it without the resistor. I changed the resistor when I did mine but I didn't find any issues with the old resistor. All the values were very similar to the new one. And to top it off, it's a pain in the butt to change it under the dash
     
    #10 JC91006, May 4, 2025 at 12:39 PM
  11. Horseflesh

    Horseflesh New Member

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    I'll discuss the resistor issue with the mechanic. It seems plausible a resistor could last for a long, long time.
     
    #11 Horseflesh, May 4, 2025 at 12:44 PM
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