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C1241 Code with Freeze Frames - Seeking Diagnosis Assistance

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by mikk, Aug 6, 2024 at 7:21 PM.

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  1. mikk

    mikk New Member

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    Hello everyone,

    I've been experiencing an issue with my Prius, and I'm hoping to get some advice. Approximately once a month, all the brake warning lights (both red and yellow) illuminate on my dashboard. This happens in two scenarios:

    1. Parking Scenario: Most often, when I start the car while parked, the warning lights appear. However, if I turn the car off and then back on, the warnings disappear, and I can drive without any issues.

    2. Driving Scenario: Occasionally, the warning lights come on while I'm driving. In this case, I stop the car, turn it off, then back on, and the warnings vanish, allowing me to continue driving.

    The error code I consistently receive is C1241, which indicates either low battery positive voltage or abnormally high battery positive voltage.

    I've collected three freeze frames related to this issue, which I've attached as PDF files to this post. While analyzing these freeze frames, I've observed the following:

    1. The front right (Fr) wheel cylinder consistently shows an extremely low voltage (around 0.01 V) compared to the other wheels (which read around 0.45 V).

    2. The Fr wheel consistently displays a different speed.

    3. Strangely, the vehicle speed always matches the Fr wheel speed. How can this be?

    In the most recent freeze frame, the vehicle speed and Fr wheel speed were both 1 km/h, while the other wheels showed 23 km/h.

    4. Additionally, the voltage of the "Master cylinder sensor2" and the Fr wheel cylinder is equal (around 0.01 V or 0.03 V). Is this normal? It seems unusual to me, similar to the previous observation (see item 3).

    As a layman, this is what I've been able to identify. Perhaps there are other anomalies I haven't noticed.

    I plan to take my Prius to a reliable car repair shop where they're cooperative and willing to investigate the issue together. Unfortunately, the nearby Toyota shops haven't been very competent.

    I'm seeking advice on what might be wrong with my Prius and which parts should be checked or replaced.

    Any insights or recommendations would be greatly appreciated!

    Thank you in advance for your help!
     

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    #1 mikk, Aug 6, 2024 at 7:21 PM
  2. dolj

    dolj Senior Member

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    This is somewhat similar to a comment ChapmanF made in this post in another thread for the same DTC.

    Your numbers are slightly different in that you have the XX2 data points (for 3 out of 4) showing reasonable values and the XX1 data points showing suspicious values. That is :
    IG1 voltage 0.00 V vs IG2 voltage 10.37 V
    BS1 0.07 V vs BS2 10.76 V
    +B1 0.07 V vs +B2 10.50 V

    BS1 relates the ABS No. 1 relay and BS2 relates to the ABS No. 2 relay. You might want to check you have voltage at the ABS No 1 relay and that this relay functions correctly.

    The other notable anomaly mentioned in Chap's post is the value of the detailed freeze DTC. As a programmer 256 (2^8) and 512 (2^9) stand out as possible translation error defaults. As Chap mentions, the FFD detail code should be 81, 82, 83, or 84. While this is unhelpful and may be a needless distraction, I believe that looking into what is causing the voltage discrepancy on those voltage input lines might be productive.

    Before starting any diagnostic effort, ensure the 12 V battery is fully charged and tested that it holds voltage under load.

    You might find the attached troubleshooting inspection procedure that contains the wiring diagram excerpt for this DTC.
     

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    #2 dolj, Aug 7, 2024 at 4:19 AM
    Last edited: Aug 7, 2024 at 10:57 AM
  3. Tombukt2

    Tombukt2 Senior Member

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    Seems like the 10 volts up there that's repeated in the testing seems to come back to some sort of battery or ABS power issue seems uncanny how that works out or it seems it does
     
    #3 Tombukt2, Aug 7, 2024 at 8:08 AM
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