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ABS pump stays running after power off

Discussion in 'Gen 2 Prius Main Forum' started by windrider, Apr 1, 2022.

  1. windrider

    windrider Junior Member

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    Hi long time member but not a frequent poster. Good forum here for us do it yourselfers.

    I have a 07 Prius with 180K miles, after turning the car off the accumulator pump stays cycling.

    It is not just continuously running, it is building pressure then stops but stays cycling.

    I remove the 12v battery cable then put it back on, problem solved...until I start the car again.

    At first I was like maybe it was the door switch but it seems to be working fine
    Possibly the fob (?) not sure, did a search on prius chat nothing really came up.

    I do have a problem with the key fob not working 100%,
    I purchased two from UHS locksmith *(the ones that locksmith told me to get) and cloned them using tech stream. They work if inserted but will not unlock the door. No remote recognition to open doors.

    Best I can figure is that the original remote was not a "master" so the door locks cannot be copied
    not sure the problem might be resolved by the locksmith ($100-150)

    The speedometer dash display went out, though that the repair had something to do with this mystery pump staying on. but not

    History-
    No codes for ABS pump on tech stream few for AC

    Yes brake fluid reservoir is full

    Front brake pads were replaced and rear shoes, rear brakes and front were bled out after (wheel cylinder piston slipped out a little)

    Originally the traction battery needed repair and registration was out,
    also later the dash display odometer went blank.

    I repaired the HV battery with some e bay cells, ended up having to remove it again since a few of them weren't great, so after third time battery is great.

    The odometer/dash display I removed and replaced the capacitor with a 100 uf works fine now

    12v battery tested with electronic tester to be in good shape

    anyone have any experience with this one? I have owned repaired about 6 Prius none have had this problem even the two that had bad accumulators did not do this
     
    #1 windrider, Apr 1, 2022
    Last edited: Apr 1, 2022
  2. prius16

    prius16 Active Member

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    On Techstream, can't you see live data on what the pressure is for the ABS pressure accumulator?
    Sounds like a pressure accumulator leak.

    Good Luck!
     
    #2 prius16, Apr 1, 2022
  3. windrider

    windrider Junior Member

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    Hi

    Thanks for your reply. Yes I will check the pressure and hopefully there's some new codes.

    Pressure builds then stops then cycles as most do..not like new though.

    If the accumulator has low pressure would it still stay running after powering off?

    Might have to look at the schematic see what's powering the main start stop relay.

    I had the pump fail on two Prius the last one was on a 2008 no issues with the pump turning off,

    the one before was on my 2012 at 130k miles, pump turned off. Pricey parts.

    now thinking a sticky relay? (but it turns on) or something with the key fob
     
    #3 windrider, Apr 1, 2022
  4. prius16

    prius16 Active Member

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    I'm not that familiar with the Toyota Prius ABS system.
    Iirc, it's mainly a Toyota system, and not a Bosch/etc system.

    In general the ABS system gets constant (12V) battery power.
    In a typical car, if the engine stalls/stops/dies/breaks, you still want/need ABS.
    However, if the car is off, the ABS system shouldn't keep trying to pressurize the accumulator. The ABS might try for a few seconds after the key is shut off, just to have the system primed for start-up (and potentially a weaker battery).

    The pump gets controlled by the computer.
    In general, there might be a relay for ABS general/overall power.
    I doubt that there's a relay between the computer and the pressure pump.


    Unless others are familiar with this type of issue, Techstream is the best bet, to reduce the chance of un-needed parts replacement.

    Good Luck!
     
    #4 prius16, Apr 1, 2022
  5. ChapmanF

    ChapmanF Senior Member

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    I think the brake system stays awake for more like a couple minutes after the car is powered off; at least in my Gen 3 it does. Maybe its sleep timer gets reset when it has to pump back up, so it isn't ever timing out the two minutes and going to sleep?

    It also wakes up as soon as the driver's door is opened.
     
    #5 ChapmanF, Apr 1, 2022
  6. JoeB

    JoeB Junior Member

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    The reason you are hearing it is not likely an electronic fault but because the accumulator is leaking and needs to be replaced. The Gen 2 Prius ABS module fails over time for the same reason all ABS modules fail in older cars--the actuator seals gradually no longer can keep their pressure for very long. In a Prius, the primary symptom is the frequent refilling of the actuator even when the power is off. The Prius will keep the actuator pressure at a minimum level regardless of whether the power is "on" or not for emergency braking unless the hybrid battery is actually unplugged. Then it will simply bleed out completely and repressurized when the battery is plugged back in (via the orange safety plug).

    Used brake ABS units exist, although with shorter lifespans than a new one. I recently successfully replaced mine with a used module--it is a lot of work, but doable.
     
    #6 JoeB, Apr 5, 2022
  7. ChapmanF

    ChapmanF Senior Member

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    A few things:

    The accumulator pump runs on 12 volts, not 200 volts. It is powered by the car's 12 volt system, and does not rely on the traction battery.

    Whenever the car is OFF (or in any mode except READY), the traction battery is completely disconnected, so it can't be powering anything then.

    The brake system normally does go to sleep, a couple minutes after the car is powered OFF. Then the pressure in the accumulator does normally bleed out. When there isn't a serious leak, that usually takes some hours.

    The brake system wakes up again as soon as the driver's door is opened. It is normal to hear the brake pump run then (at least if the car has been OFF for some time), replacing the pressure that bled off while the system was asleep.

    If the pump does continue to cycle for more than a couple minutes after the car is powered off, it likely means that the cycling itself is preventing the system from sleeping.
     
    #7 ChapmanF, Apr 5, 2022
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