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C1391 and brake fluid level

Discussion in 'Gen 3 Prius Technical Discussion' started by OC63RAG, Mar 30, 2023.

  1. OC63RAG

    OC63RAG Member

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    2013 Prius with 180K miles, the dash warning lights came on for the brakes and I had the codes pulled up. C1391 - Abnormal leak of ACC Press
    C1464 - Front Speed Sensor RH Circuit
    C1465 - Left Front Speed Sensor

    I replaced the wheel speed sensors (quick and inexpensive) hoping the warning lights would go away. I cleared the codes using the jumper method and after about 15 minutes of driving, the lights came back on.

    I read up on the accumulator issues and called Toyota corporate to see if they'd offer a goodwill repair, no dice. Over 150K miles, they didn't want to do anything else (local dealers had the same reply).

    I noticed the brake fluid was low in the reservoir (right around the mid level mark) and topped it off to the max level mark.

    After driving for about 10 minutes, the lights went off, the brake pedal felt great and the sound of the ABS cycling went away.

    Is the problem solved or did I just put a bandaid on the issue by topping off the brake fluid?
     
    #1 OC63RAG, Mar 30, 2023
  2. bisco

    bisco cookie crumbler

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    depends on how quickly it is disappearing. keep a close eye on it
     
    #2 bisco, Mar 30, 2023
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  3. OC63RAG

    OC63RAG Member

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    Will do. If the accumulator is bad, would the fluid be leaking at some point? I can't see any signs of leakage but it has to be going somewhere.
     
    #3 OC63RAG, Mar 30, 2023
  4. bisco

    bisco cookie crumbler

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    tbh, i don't recall leaking fluid in any of the threads i've read, but it may be the case. check all the wheel connections as well.
    how long time/miles has it been since you last noticed the fluid level?
     
    #4 bisco, Mar 30, 2023
  5. OC63RAG

    OC63RAG Member

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    I honestly don't remember as it's been trouble free (no reason to check it).
     
    #5 OC63RAG, Mar 30, 2023
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  6. bisco

    bisco cookie crumbler

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    that's what i was thinking. i never check mine either. hopefully, it's just typical loss over 17 years, and it got low enough to set a code
     
    #6 bisco, Mar 30, 2023
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  7. ChapmanF

    ChapmanF Senior Member

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    Most of the time, a C1391 code will turn out to be an internal leak. You would never see any fluid going out of the system; it is just getting around the valves inside and trickling back to the reservoir.

    A level below MAX at the reservoir is normal and expected if the system hasn't been zeroed down. Did you zero it down before you checked and topped off?

    When the system normally runs, it pumps some fluid out of the reservoir and into the pressurized accumulator, so the reservoir level goes down. To "zero-down" means to have all the accumulator pressure released so that the fluid is back in the reservoir. The level markings on the reservoir are meant to be checked while zeroed down. If you top off to MAX while it isn't, you'll be slightly overfilled.

    The level also gradually drops as the brake pads wear (in addition to the way it drops when not zeroed down). At the factory, it started out at MAX when the pressure was zeroed down and the pads were brand new.

    So from the level you described, I'm not convinced it was even low, necessarily. That makes me cautious about assuming that your topping-off will be a lasting fix.
     
    #7 ChapmanF, Mar 30, 2023
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  8. aspiringnobody

    aspiringnobody Junior Member

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    I was over by a few hundred miles and they told me to get stuffed. Last Toyota I'll ever buy (new at least). They will get exactly none of my money ever again.
     
    #8 aspiringnobody, Mar 30, 2023
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  9. bisco

    bisco cookie crumbler

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    only problem being, no other mfg will either
     
    #9 bisco, Mar 30, 2023
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