seeking assistance troubleshooting intermittent brake warning c1241, c1256

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by deadmandave, Jul 30, 2025 at 7:32 PM.

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  1. deadmandave

    deadmandave New Member

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    Greetings,

    My 2009 Prius has a very intermittent brake issue. maybe 3 times it has done the following:

    "Brake" light on dash illuminates, ! Abs shows up on the touchscreen and a loud alarm is sounding.

    This is resolved by a shutdown and restart. However one time there was no safe area to pullover and after a few minutes of driving with this alarm, brake power was reduced but not gone altogether.

    I took the car to a shop to run techstream and they found c1241 and c1256 and quoted 2600 to replace the brake actuator.

    The brake actuator acts normal at all other times imo. It runs for a few seconds on startup and when the brake pedal is depressed then it holds pressure and won't run again until a few minutes later. brake pressure is consistent and trouble codes/lights are not a common experience.

    I've checked what Ive thought of or what's easy,

    Brake juice is full
    Brake pedal switches are within spec
    12v battery is charged and healthy
    Engine ground is good

    This car has 130k miles. Had a new hybrid battery put in last year (maybe that's when the issue started?)

    Often the display screen is restarting (annoying yes. Related?)

    Possible water damage in the car? Slight rust/corrosion on some components in engine bay

    W hat else can I check before replacing the actuator, or should I just replace it? Abs module ground? Loose connections?

    Thanks Screenshot_20250730-163056.png
     

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    #1 deadmandave, Jul 30, 2025 at 7:32 PM
  2. Tombukt2

    Tombukt2 Senior Member

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    I'm going to have to guess a used actuator maybe? Because the 56 ending code is pressure in the system pump or accumulator..... Pressure issue .
     
    #2 Tombukt2, Jul 31, 2025 at 7:15 AM
  3. ChapmanF

    ChapmanF Senior Member

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    I would lean toward troubleshooting the C1241 first: inadequate electrical power getting to the brake components.

    Electrical power is needed to keep the pressure up, so having a second code about the pressure doesn't have to mean something else is wrong too.
     
    #3 ChapmanF, Jul 31, 2025 at 7:43 AM
  4. deadmandave

    deadmandave New Member

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    I agree that the low or high voltage could cause a drop in pressure.

    Any advice into how to troubleshoot the c1241?

    We bought this car used with 115k miles on it. Not sure if the accumulator was ever replaced but my gut feeling is that it's original.
     
    #4 deadmandave, Jul 31, 2025 at 11:04 PM
  5. Tombukt2

    Tombukt2 Senior Member

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    So the question remains is your power to the brake system stable your 12 volt is it worth a darn . This is important in the Prius this can mess everything up you'll be chasing $1,000 parts and only need a $300 or less battery so.
     
    #5 Tombukt2, Aug 1, 2025 at 12:21 PM
  6. ChapmanF

    ChapmanF Senior Member

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    C1241 is a code about the electrical power reaching the brake hardware. I'm not saying it can't ever have to do with the 12-volt battery, but (especially if you get the code when the car is READY and the power isn't coming from the 12-volt battery) it can just as easily be about wiring anywhere on the path to the hardware under the hood.

    The troubleshooting steps are in the repair manual under C1241.

    Toyota Service Information and Where To Find It | PriusChat

    There should be threads about it here if you search.

    If I remember right, the gen 2 skid ECU is structured as a redundant pair of systems that monitor each other, and have their own separate electrical supply connections, and the INF codes for C1241 help to tell you which system was detecting a weird voltage reading for the other.
     
    #6 ChapmanF, Aug 1, 2025 at 2:06 PM
  7. Tombukt2

    Tombukt2 Senior Member

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    But the brakes run on the 12 volt battery not the HV or I guess when ready they can run off the little black box and the not 12 volt because the DC to DC doodads making ya 14.5 as long as cars on. Probably not a superpower hog like the headlights I guess.
     
    #7 Tombukt2, Aug 1, 2025 at 2:55 PM
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