Gen 2 won't shift from Park to Drive or Reverse with C1256?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Dinoman, May 14, 2025.

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  1. Dinoman

    Dinoman New Member

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    History of major car repairs .. .have replaced main battery pack. Have replaced instrument cluster electronics with reconditioned electrical board. (was giving weird display codes then blank display) Has been good driving for past year. Then after a bit of rain (car is normally parked outside), I stopped at a light and put the car into park. A whole bunch of warning lights came on, along with the red triangle warning light. I stopped at a 7-11 to recycle the electronics (shut car off then on again). The car turned on again, but, the engine didn't turn on, and the car won't shift out of Park (only to Neutral) to Drive or Reverse. It's dead in the water. I've tried holding the brake pedal hard, (the brake lights come on), but, nothing will get the car to shirt into Drive or Reverse. I had the car towed home. (I have a spare car to use for now). I put a OBDII scanner on it and it's showing a C1256 code (brake accumulator low pressure). Brake fluid level is normal. Voltage is 11.5 or so. I tried jumping the battery (replaced about 1-2 years ago), but, it still won't shift into Drive or Reverse? Brake pump seems to be humming away when I turn on start button, and doesn't seem to stop? It seems strange to me that the Brake accumulator would cause the car not to shift out of Park? Could I have a problem with the reconditioned instrument cluster electronics again? Multiple problems at once? I'm trying to figure out an attack plan.
     
    #1 Dinoman, May 14, 2025
  2. dolj

    dolj Senior Member

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    The C1256 has two sub-codes (INF codes) – 141 and 143.

    The conditions to set with the 141 INF code are:

    When either condition below is met:
    • Braking operation is input when the accumulator pressure is less than 12.45 MPa and the vehicle speed is input (the detected value changes if the accumulator pressure is low after system start).
    • Accumulator pressure is less than 14.62 MPa for 120 seconds (changes according to power source voltage) after system start (it stores the DTC after the conditions are met, and drives the buzzer).
    The conditions to set with the 143 INF code are:

    When one of the following conditions is met:
    • Any of the wheel cylinder pressure sensor values are lower than the target value for at least 0.5 seconds when the accumulator pressure is less than 14.62 MPa and the vehicle speed is input.
    • Accumulator pressure changes little when the accumulator pressure is less than 14.62 MPa for at least 1 sec. without braking (and the pump motor is operating).
    • Accumulator pressure is less than 14.62 MPa for at least 0.5 seconds when the motor relay is malfunctioning.
    If you can get the INF code, it would help you to focus on the correct area.

    Regardless of the INF code, the trouble area is the brake actuator assembly (accumulator pressure, accumulator pressure sensor, pump motor).
    The most likely reason is that it is not safe to drive the car in this condition.

    This code has nothing to do with the reconditioned instrument cluster electronics.

    I'm not sure why you seem to find it hard to believe you can have more than one fault at a time, but there you go.
     
    #2 dolj, May 15, 2025
    Last edited: May 15, 2025
    Brian1954 likes this.
  3. Tombukt2

    Tombukt2 Senior Member

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    I also find that kind of hard to believe I think something else might be going on as far as I know when my accumulator and break actuator were failing so badly that applying the brakes would cause one of the front calipers the honk and one of the rear wheel drums wasn't even grabbing properly the car would turn sideways almost breaking it was like one caliper and one drum were working I drove this car like this for about a week seriously the gold car my work vehicle and I still have it replace the actuator and the braking became normal with the car always started and ran even when I drove to 45 miles with a near dead hybrid battery engine running and fan on all the time to pick up a new one no problem starting and driving I don't think it's just my vehicle. If you take that cheat code scanner and you clear the codes and then immediately after that you clear the codes again even there if there aren't any now push the start button did the car just start and ready if so that indicates another problem
     
    #3 Tombukt2, May 15, 2025
  4. Dinoman

    Dinoman New Member

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    #4 Dinoman, May 24, 2025 at 6:36 PM
  5. Dinoman

    Dinoman New Member

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    update to problem .. fixed car.. but, unknown what caused the fix?
    1) Car's display was going dark and intermittant, weird dash error lights showing up.
    2) In Jan 2025 instrument electronic module was replaced with reconditioned unit.
    3) Suddenly after rain for a few days car's dash error lights with RED triangle came on.
    Car was stopped and then restarted to try and clear codes but, car wouldn't shift to
    Drive or Reverse.
    4) Car towed after after attempt at jump starting wouldn't let car out of Park to Drive or Reverse.
    5) Car scanner (Autel scanner) showed C1256 (Brake Accumulator) code. Brought battery to auto store.
    Battery wouldn't hold charge, new battery swapped out (Battery only 3 months old DieHard AGM)
    6) After installing New Battery still not able to shift out of Park. Played with scan tool for a
    while trying to gather more recent data. Clicking of (Brake pump to accumulator) sound when car
    turned on. Suddenly, car was A-OK again. Battery voltage 14.4 volts.
    7) How do I diagnose working car now? It may be related to rain causing electrical short? Is Brake
    Accumulator on it's last legs? Bad alternator in the rain, not charging battery? How do I monitor
    for future electrical problems? I have voltage monitor in cigarette lighter socket now. Why didn't
    jump starting from tow truck fix the problem when it tried? Still rain causing some electrical short
    in instrument electronic control module? What battery monitor, charger should I buy? What diagnostic
    scan tool? (I'm not that happy with Autel scan tool. I have to have internet with my phone to use it,
    and it seems to drop bluetooth connection every so often. I'd prefer a hard wired connection).
     
    #5 Dinoman, May 24, 2025 at 6:37 PM
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