Need some help tackling a rear ABS wheel speed wiring harness replacement.

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by h1ph0panonymous, Aug 4, 2025 at 8:33 PM.

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  1. h1ph0panonymous

    h1ph0panonymous Member

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    I have an idea where the rest of the wire leads to through the wheel well (into the trunk in the corners like where battery sits) but the rears don’t have a wheel well cowl on my model and year? It’s plastered with some sort of rubber material and even more where the wiring harness goes through the wheel well. Do I cut through it with something (what exactly do I use to open or cut it open or not?) to get the new wiring harness in to plug it up to the ECU bus in the trunk but most importantly what exactly is that rubber material? (So I can replicate the plaster and patch with that same rubber like weather sealing material)
     
    #1 h1ph0panonymous, Aug 4, 2025 at 8:33 PM
  2. PriusCamper

    PriusCamper Senior Member

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    That sounds about right... Other thing you can do is look at as many images of that part that you can find online and confirm if it always comes with plug attached and not just bare wires and that will confirm that cutting through that material and then sealing it back up is the proper way to do it. Of course you could upgrade by replacing a portion of that material with a grommet.
     
    #2 PriusCamper, Aug 4, 2025 at 10:37 PM
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  3. h1ph0panonymous

    h1ph0panonymous Member

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    Thank you. I can’t find anything online about the Gen 3 Prius repair for this exact replacement harness so I’m just guessing from here, would you use an exact knife for this if you were doing it, can’t imagine anything else that could be thin and sharp enough to work around the wire and not cut anything else on accident. I did find “universal” splice job videos but comments all say these harnesses are Ohm sensitive by 1 Ohm, I have no clue how much length of wire equals one Ohm. I might try it myself with some solder just will need to buy a solder and make sure it’s for electrical work but also an actual splice harness and not the full harness I already purchased only if find the other end in the trunk is a complete pain in the butt. I’ll update this thread for future users to search this exact repair as no one really here has done it.
     
    #3 h1ph0panonymous, Aug 5, 2025 at 2:57 AM
  4. Tombukt2

    Tombukt2 Senior Member

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    Use a plastic dowel lightly pointed to push thru the rubber 3M body shutz or it aerosol equals will seal ya back up no worries.
     
    #4 Tombukt2, Aug 5, 2025 at 9:06 AM
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  5. PriusCamper

    PriusCamper Senior Member

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    As long as you don't increase or decrease the length of the wires the Ohms should stay the same... Of course the ohm could change dramatically if don't do a good soldering job.
     
    #5 PriusCamper, Aug 5, 2025 at 2:04 PM
  6. ChapmanF

    ChapmanF Senior Member

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    If this is a gen 3 thread, the gen 3 wheel speed sensors make fixed-amplitude, logic-level signals. I'm skeptical of any comments you're finding that say the resistance is all that critical. The normal attention you would pay to not making a bad splice ought to be enough.

    The skid ECU has an extra-sensitive Signal Check Mode you can place it into and drive around for a bit and see if it detects any hints of problems. The repair manual says to use this mode after any replacement of the bearings or speed sensors anyway. If you get through that extra-sensitive check, passing, you can be quite confident of your repair for normal use.
     
    #6 ChapmanF, Aug 5, 2025 at 2:18 PM
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  7. h1ph0panonymous

    h1ph0panonymous Member

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    It was a universal splice YouTube video for abs harnesses that I read the comments in saying these types of wirings are Ohm sensitive up to one Ohm sensitivity. I might just buy the splice versions they have on rock auto and try that first but I sure as heck would like my regen braking back as soon as possible, my hybrid battery is probably getting weaker and weaker without it (2000 miles since disabled), relying on engine-to-inverter energy too much for a recharge, I’m guessing that can’t be healthy for it or lacking a maintaining of it without that extra recharge it gives from braking. I’ll just research proper splice and solder jobs so I know what type of solder metal I need and the correct technique.
     
    #7 h1ph0panonymous, Aug 5, 2025 at 4:17 PM
  8. PriusTech

    PriusTech Member

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    You shouldn't have to cut any insulation or plastic parts, and you should NEVER cut or splice any ABS wiring, I don't care what people are doing on youtube

    Here's a factory service manual in PDF (you have to pay to see pics)
    https://www.allcarmanuals.com/factory-service-manual-286-Toyota-Prius-XW30-ZVW30.html

    Does TIS have access to service manuals?

    On page 1220 it says you have to remove all the stuff on the rear floor, Like where the spare usually is and you should see the wiring coming through the wheel well.

    I would just start removing interior trim. you'll eventually find the wire. It should be a 2 wire harness, and you are looking for a 2 pin connector, it will be inside the vehicle, not outside.
     
    #8 PriusTech, Aug 5, 2025 at 6:07 PM
    Last edited: Aug 5, 2025 at 6:21 PM
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  9. h1ph0panonymous

    h1ph0panonymous Member

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    Sounds easier than what I’ve read, thank you. Hoping you are right, now to plan how to carefully force the old harness out of the wheel well weathering material thats practically glueing it in place and then repatch or grommet the new harness through that hole or entry where old harness had material protecting it from humidity and water entering the interior, sorry for my Dunning-Kruger mechanic terminology.
     
    #9 h1ph0panonymous, Aug 5, 2025 at 6:16 PM
  10. PriusTech

    PriusTech Member

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    No I'm wrong it looks like it connects outside the vehicle, it's number 24 in this parts pic. So the connector is outside the vehicle, probably clipped onto the suspension or the body where it goes through the body. Just follow it from the sensor. Unless that's a grommet at the top of the harness in the pic ;>). Your mileage may vary if the dealer sprayed a bunch of aftermarket undercoating. 8527745.png
     
    #10 PriusTech, Aug 5, 2025 at 6:32 PM
    Last edited: Aug 5, 2025 at 6:50 PM
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  11. PriusCamper

    PriusCamper Senior Member

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    I think Chapman reply above is probably more correct than saying you should NEVER cut or splice ABS. As in the type of signal that travels on those wires isn't that vulnerable to a spliced wire and Chapman had a great suggestion on how to test the problem.
     
    #11 PriusCamper, Aug 5, 2025 at 6:35 PM
  12. PriusTech

    PriusTech Member

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    PASS. OR DRIVE?

    You probably want a small pic set also, to unclip the harness from it's mount points, or at least a pocket screwdriver.
     
    #12 PriusTech, Aug 5, 2025 at 6:50 PM
    Last edited: Aug 5, 2025 at 7:00 PM
  13. PriusTech

    PriusTech Member

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    When Japanese engineers say to never cut any ABS harness. And there's no reason to, there's always a connector. You can do whatever you want, it's your vehicle.....
     
    #13 PriusTech, Aug 5, 2025 at 6:52 PM
  14. h1ph0panonymous

    h1ph0panonymous Member

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    I’ll take pictures of what I mean about where the harness passes through the wheel well into the interior of the trunk, my Prius gen 3 doesn’t have a wheel well cover, its wheel well cover is some sort of plastered on rubber to the hull of the car. Yes number 24 is what I bought, the second most expensive one on rock auto to be exact but they also sell half harnesses (halfsies) to splice ONTO the harness in case you destroyed your connector that connects to the sensor in the wheel hub.
     
    #14 h1ph0panonymous, Aug 5, 2025 at 7:02 PM
  15. PriusTech

    PriusTech Member

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    Okay, I just jacked up and looked at my 2011 CT200H which is supposedly gen 3 Prius underneath.

    So both rear ABS harnesses go through the wheel well at the top front of the wheel (2:00 on pass, 10:00 on drive) and connect INSIDE the car at 12:00, level with the top of the tire. And I was wrong again, it's ONE wire with a white one wire connector.

    I currently have my hybrid battery removed with all the parts pulled in the lower spare tire area, so I can see the connector under the inside wheel well cover.
     
    #15 PriusTech, Aug 5, 2025 at 7:36 PM
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  16. h1ph0panonymous

    h1ph0panonymous Member

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    Do you see the rubberized undercoating plastered everywhere? There is a thicker application of it where the harness passes through it, I’m guessing I cut an oval or square to get the harness out of that material.
     
    #16 h1ph0panonymous, Aug 5, 2025 at 7:43 PM
  17. PriusTech

    PriusTech Member

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    LEXUS-ABS.png
    The CT200h part is close to the same as the Prius. Most likely the connector is inside. If they can they usually put them inside where it's not as wet.
     
    #17 PriusTech, Aug 5, 2025 at 7:45 PM
  18. PriusTech

    PriusTech Member

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    the Lexus has a removable exterior wheel well liner

    I would just get a screwdriver and dig into the undercoating. Or maybe try some WD-40 to soften it up.

    That's most likely dealer aftermarket undercoating. The factory won't usually spray a harness where it goes through the body. (Minnesota, yeah. ;>)
     
    #18 PriusTech, Aug 5, 2025 at 7:49 PM
    Last edited: Aug 5, 2025 at 8:11 PM
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  19. h1ph0panonymous

    h1ph0panonymous Member

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    Thanks for all the physical confirmations, I was hoping the inside of the trunk part of the job wasn’t going to be hard but pulling all the storage compartments to expose it sounds like a easy job (thought I was in for more work than that like stripping interior walls or something like that) so I’ll actually cut through the exterior undercoating from the interior of the trunk since I’ll be able to see how big of a hole will be big enough for the connector to fit through. Sounds easy now, thank you so much. I’m a pessimist and over planner before doing things so this helped.
     
    #19 h1ph0panonymous, Aug 5, 2025 at 7:54 PM
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  20. ChapmanF

    ChapmanF Senior Member

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    I can't recall seeing any admonition to that effect in the Prius repair manuals. I haven't specifically looked for it just now, so I'm open to being shown wrong, but I've looked in the manuals a lot without noticing it.

    SRS (airbag system) harnesses, the bright yellow wiring, yes, they do strictly advise against splices there.
     
    #20 ChapmanF, Aug 5, 2025 at 8:54 PM
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