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Continuous Flashing Hazards and now ABS Failure

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Durantchula, Aug 15, 2024.

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  1. Durantchula

    Durantchula New Member

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    Awhile back, I my 2010 gen 3 Prius began flashing hazards uncontrollably making the car pretty much undrivable. Based on some other posts on this forum, I cut the wire HZRI (light blue) which stopped the flashing. Shortly after cutting the wire, the dahsboard lit up with the ABS, Brake and Traction Control warnings. The lights imitated the scenario of when one of the speed sensors fails. When I took it to the shop for state inspection, the shop noted that codes indicated the rear right speed sensor had failed. I replaced the sensor and bearing with after market parts but the code persists according to the shop. The shop now suggests that the part is faulty and should be replaced under warranty. I find this all a bit convenient as the lights came on after cutting the wire leading into the ABS module. My question is, would cutting the wire cause the speed sensor codes or should I believe the shop that the part is faulty.
     
    #1 Durantchula, Aug 15, 2024
  2. Durantchula

    Durantchula New Member

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    #2 Durantchula, Aug 15, 2024
  3. bisco

    bisco cookie crumbler

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    in post #9, he says he unplugged a wire from the abs. is that the wire you cut?
     
    #3 bisco, Aug 16, 2024
  4. ChapmanF

    ChapmanF Senior Member

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    It's tough to say what that "scenario" is, given that you get the same lights for a whole lot of different brake system issues (and even some non-brake-system issues that the brake system ends up knowing about). It's the trouble codes that reveal what the issue is. So it is good that the shop did this:

    However, people sometimes read too much into a trouble code. An ECU in a car can only tell you things it would have some way of knowing. If the signal coming into the ECU from a wheel speed sensor seems weird, the ECU can tell you that. But it can't tell you why it's weird. A human needs to figure that out. Is the sensor itself bad? Is there damage to the wiring from the sensor to the ECU at the front of the car? Or is something wrong in the ECU itself? All those things are possible, and the code doesn't say which is the answer for you.

    Cutting the sky-blue HZRI wire will not have caused any speed sensor codes.

    If the sensor was replaced the first time just assuming it was the reason for the code, before checking other possibilities like the wiring from the sensor to the front, it's possible the sensor never was the original problem, and the real problem still is whatever it was. That would make this a good time to work through the troubleshooting steps for the code and try to pin down what the real cause is. (Not saying it can't be another bad sensor! Such things can happen. But you'll know, if you go through the troubleshooting steps and that's where they lead.)

    One more possibility not to leave out: we know the sky-blue HZRI wire got cut for a reason. It got cut because the ECU was putting a goofy signal on it causing the lights to flash; that definitely is a failure of a circuit inside the ECU. Cutting the wire stops the goofy signal from reaching the lights to flash them. But it doesn't heal the ECU. We know for sure one thing has gone wrong inside that ECU.

    If it were to turn out that the wheel-speed-sensor error is also caused by something (else) going wrong inside that ECU, that wouldn't be too hard to believe.
     
    #4 ChapmanF, Aug 16, 2024
  5. Durantchula

    Durantchula New Member

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    I cut the sky blue HZRI wire as discussed later in the post. It’s not exactly clear what wire post #9 unplugged.
     
    #5 Durantchula, Aug 17, 2024
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  6. Durantchula

    Durantchula New Member

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    I did test the continuity of the wiring from the speed sensor to the inside of the car. I did not test the wiring to the ECU or wherever it goes. Perhaps I dislodged something when messing around the ABS actuator. Anyone have ABS wiring diagrams handy? It’s easy enough to test the speed sensor so I will do that first.
     
    #6 Durantchula, Aug 17, 2024
  7. Durantchula

    Durantchula New Member

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    Took some time to test the speed sensor and wire continuity. Speed sensor reads 3.6 MOhms on the replaced sensor and 4.1 MOhms on the left (OEM). I believe that discrepancy to be within tolerance. On the right side, I tested the black and white wires coming from the ECU and connected to a ground. The black and white wires read 6.0V and ~12V respectively which makes sense. So I am now a bit stumped...This has me thinking the issue may be within the brake ECU (Actuator) hence the original hazard issue. One last check is to test the terminals plugging into the brake actuator but I don't expect to gain much from that since I already tested the wires at the speed sensor connector above the wheel well.

    Before I start to pursue replacing the brake actuator which is an undertaking and cost, is there anything I can do do test the actuator to confirm it's bad?
     
    #7 Durantchula, Aug 20, 2024
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