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u0100 what to look for?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Danny13pruisc3, Jun 27, 2021.

  1. Danny13pruisc3

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    2012 Prius c
    Model:
    Three
    Have you had the u0100 ? what turned out to be the problem and solution?

    on Youtube a guy says check all the connections in both kick panels

    and i know to check the fuses of course..

    It's my buddy's car and i think it's an 04 or 05.. 05 i think..

    I'm supposed to be picking up an 06 tomorrow and we can use that for diagnostic parts..

    if the PCM is bad, is it easy to swap ? where is it located?

    I know my next step is to hook up techstream and get the codes..

    OH BTW He replaced both the 12v with a new one, and the traction battery with greenbean..
    GB claims they got code u0100 and that's it... so i'm wondering if i'll get anything else with techstream..
     
  2. mr_guy_mann

    mr_guy_mann Senior Member

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    What symptoms do you have with the car? Does it drive? Any warning lights? Be aware that there can be a number of "minor" but important differences in electrical parts from 04-05 Prius to 06-09. Some things you can swap without problem, while others might have different wiring.

    You absolutely need to have all the codes with descriptions from ALL the computers on the car via Techstream. Particularly which ecu set what comm error code for not being able to "talk" to which other ecu.

    In order for a data network to function, each ecu connected needs; power, ground, and comm lines. So you will have to use the diagnostic write up and the wiring diagrams in the factory service manual to figure out if your problem is a wiring fault to a particular ecu, or if a ecu is bad.

    FYI, I often find corrosion damage at a connector (or a ground wire) somewhere causing U codes. If I get low voltage codes as well then I look at the 12V battery.

    Posted via the PriusChat mobile app.
     
  3. Danny13pruisc3

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    Turned out to be a bad relay integration module
     
  4. Danny13pruisc3

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    Update: car still has the problem.. charging the battery.. going to scan it again.
     
  5. ChapmanF

    ChapmanF Senior Member

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    Unless your plan is just to get lucky and spot a bad connection somewhere by looking at it, for communication codes you kind of need to be in the Repair Manual in the NETWORKING -> CAN Communication System section.

    I don't have a c, but in the Gen 3 liftback there are three different CAN networks (four if you have the advanced parking or DRCC stuff). The networks are assembled through several multi-port CAN junction connectors behind the dash; the manual shows which one is which, and which port is which, and which wire colors go with which. Some of the ECUs are on more than one of the networks.

    U0100 always means "I can't talk to the ECM", but what it's really telling you also depends on who says it. In a liftback, things that can say "U0100" include:

    • Power management ECU (displayed in Techstream as "Hybrid Control")
    • Power management ECU (displayed in Techstream as "Power Management2"
    • Body ECU (if you have remote A/C or LED headlights)
    • Certification ECU (smart access/smart key/wireless)
    • A/C amplifier
    • Combination meter

    Yes, the power management ECU is in the list twice; if it's saying U0100 in its "hybrid control" identity, then it can't talk to the ECM over CAN bus 1. If it's saying U0100 in its "power management2" identity, then it can't talk to the ECM over the power management CAN bus.

    This section in the manual has all kinds of diagnostic rules of thumb to help you out (like, if you connect Techstream and these ECUs show up in the list and these ECUs don't, it's likely a problem here), not to mention a big "DTC combination table" helping to sort out what it means if you have such and such U codes being reported by such and such ECUs.

    There are a lot of areas of wrenching where people can dive in without the manual and pretty much come out ok, but as you can see here, there's a good chance of ending up pretty bewildered trying to do that for communication errors.

    Again, unless you luck out and find some easily visible broken wire or corroded connection or you charge the battery and everything's better, or something like that.