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2003 Prius C1251 ABS light and alarm

Discussion in 'Generation 1 Prius Discussion' started by Sharnold, Dec 18, 2019.

  1. Sharnold

    Sharnold Active Member

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    After running techstream this was the only DTC that was pulled. After clearing the DTC the alarm, abs light, and engine light will clear. At initial start up the car will not throw a DTC till you press the brake which is completely stiff no movement downward until the abs, brake, and alarm sounds again then brake pedal returns to normal minus the alarms and DTCs. Customer stated all these issues started after they replaced the 12volt battery. I suspect they connected it backwards. Does anyone have the C1251 write up? Or have any other suggestions before I start going through the fuses and relays?

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    #1 Sharnold, Dec 18, 2019
    Last edited: Dec 18, 2019
  2. ChapmanF

    ChapmanF Senior Member

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    The code refers to the electrical current drawn by the brake pressure pump. Either it is exceeding 28 amps for more than one second, or it is failing to change by more than 7 amps during the run of the pump. (Startup current for a motor is expected to be higher than running, and also the pump has to pump harder as the pressure builds up, so it's normal for the current to change, and weird if it doesn't.) The ECU knows the motor current in detail thanks to the three sensing lines (more on those in this post).

    The three troubleshooting pages in the manual more or less have you check that you can make the pump run at all (which it sounds like it does, since you do eventually get your pressure assist back), then check the resistances of the sense lines just to rule out false readings, and if the readings aren't lying, you end up at the pump motor itself.
     
    #2 ChapmanF, Dec 18, 2019
    mroberds likes this.
  3. Sharnold

    Sharnold Active Member

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    The sub code on techstream does say fault on ground. I replaced 2 ABS fuses that was blown same issue as the car is running in maintenance mode you can watch the pump shake every now and then like its cutting off then back on.

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    #3 Sharnold, Dec 20, 2019
  4. Sharnold

    Sharnold Active Member

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    #4 Sharnold, Dec 23, 2019
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