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ABS control module failure?

Discussion in 'Gen 3 Prius Main Forum' started by Elmphobia, Jun 16, 2020.

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  1. Elmphobia

    Elmphobia New Member

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    2013 Prius II with ~128,000miles. Bought used in Nov. 2019 the car was in very good condition when purchased. I did drive it about 14hr across country, but has continued to run perfectly fine. Recently, it suddenly started showing multiple warning lights - "Check hybrid system" BRAKE (red) Power Steering(!) (also red) ABS (yellow) and master warning light all at once. First mechanic could not diagnose issue and recommended going to the dealership. Dealership said the brake master cylinder needed to be replaced along with the aux battery and a lot of other "service" things like fuel injection cleaning service and valve replacement (??) but they quoted about $3,600 for all of the work. I turned down the dealership repairs due to the high cost, and replaced the aux battery myself as it was much cheaper and easier to do. That did not solve any of the issues I was seeing. I pulled codes myself - U0129 (brake system control module no communication) and P01C1 which I couldn't find any info on. I finally took it to a third place and they said that after taking it apart to confirm for sure, it is the ABS control module. Does this sound right? I am new to this and it's my first Prius and I am upset to have such an expensive issue so soon after buying the car. Was quoted $820 for used part replacement and anywhere from $1,500-1,700 for new part replacement. Any input would be greatly appreciated.

    Edit: forgot to add that the speedometer also stopped registering my speed. Mechanic said that the communication error between the ABS unit can cause all the other signal lights to be fired off from the computer due to error
     
    #1 Elmphobia, Jun 16, 2020
  2. ChapmanF

    ChapmanF Senior Member

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    The wheel speed sensors are connected to the brake ECU (it needs the information to do ABS and VSC), so yeah, the way the speedometer knows how fast you're going is the brake ECU passes the information along. If that communication isn't happening, you've got your ready-made speeding-ticket excuse right there.

    Being a U code, it's a communication error, so a person would definitely want to check the condition of the network wiring and power to the ECU before concluding that the ECU itself is shot (which is also possible). When the third place "said that after taking it apart to confirm for sure," it is the ECU, that's not very detailed on what or how they actually checked. I'm pretty sure they didn't take the ECU apart.

    There's about three pages in the repair manual (more info) about checking the network wiring, including this figure:

    U0129.png

    so naturally you'd be checking the quality of the power arriving at pin 16, the grounding at pin 28, and the CAN connections at pins 34 and 35. The CAN connections can be checked with an ohmmeter, as long as the car is powered off, really off, at least a minute passed with no disturbing of doors or windows. Because of the two paralleled 120 Ω terminations, what your ohmmeter should see between pins 34 and 35 should be in the neighborhood of 60 Ω. Might also want to measure while wiggling and flopping the connectors and wiring.

    If those were the checks your "third place" actually did, and that made them sure there's no power, grounding, or wiring issue and the ECU is really at fault, then they could be right. I would just want to be sure that's what they checked.
     
    #2 ChapmanF, Jun 16, 2020
    Johnny Cakes likes this.
  3. Elmphobia

    Elmphobia New Member

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    2013 Prius
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    Thanks a lot for your detailed and helpful reply. I of course was not knowledgeable enough to ask about this when I spoke to them on the phone before I posted this, but they said that they disassembled the car to test the module and confirm the failure. The first mechanic as well as the dealership did both bring up the ABS unit as possible or likely issue, but from speaking with the third mechanic it seems like they took the extra steps to ensure they are doing the right fixes. I don't know for sure if they checked what you stated above, but I will definitely ask them about that when I speak to them tomorrow (they've closed for the day).
     
    #3 Elmphobia, Jun 16, 2020
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