2016 Gen 4 Prius - Lost communication with ECM

Discussion in 'Gen 4 Prius Technical Discussion' started by U A, Apr 9, 2025 at 2:49 PM.

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  1. U A

    U A New Member

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    2016 Prius has a U010087 code showing lost communication with ecm/pcm a.

    The car will go into ready, but the engine will not turn on. If you plug in the obd scanner you can clear the code and then the engine will start but only for 2 seconds and will turn off again, after this the car can’t go into ready mode again unless you reset it by disconnecting and reconnecting the 12v battery.

    Any idea on where to direct attention to?
     
    #1 U A, Apr 9, 2025 at 2:49 PM
  2. BiomedO1

    BiomedO1 Senior Member

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    Your engine isn't going to run without ECU control. The 2-second start attempt is just MG1 spinning the motor - just as if you rotate an ignition key into the start position on a regular car. The engine is neither starting or running. It's going into "Ready" because the EV portion of the car is operating. By disconnecting the battery; your whacking the other ECUs over the head and making them forget there's a comms issue with the ICE ECU.
    You need to track down why the ECU isn't talking to the rest of the car. ie. rodent chewing on wires, accident, loose wiring harness, dead ECU??????
     
    #2 BiomedO1, Apr 9, 2025 at 5:45 PM
    Last edited: Apr 9, 2025 at 5:52 PM
  3. U A

    U A New Member

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    We have tried a replacement engine ecu, still no luck and have checked the wiring, no splits or anything like that, so very confusing.
     
    #3 U A, Apr 10, 2025 at 4:00 AM
  4. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Is there a procedure for swapping the ECU that involves disconnecting the aux (traction?) battery for a certain period before replacing it with a new one that you missed?

    Where did you get the replacement ECU?
    If it was from another G4 Prius, maybe put your ECU into the other Prius and see if it boots up?

    Others with more knowledge will weigh in.

    Good Luck!!
     
    #4 ETC(SS), Apr 10, 2025 at 9:58 AM
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  5. BiomedO1

    BiomedO1 Senior Member

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    On these newer cars, A ECU swap procedure must be followed - to the letter!! Most of the time, parts like that are NOT interchangeable. Don't know where you got your ECU, but for the best chances of a straight swap - The donor car must be exactly the same year, make, model, options. That's the only chance you have of making it work; if it works at all without a reprogramming. If that ECU is brand new; it definitely needs reprogramming - it's a blank slate.
    I haven't swapped a ECUs on a Prius, but I have on other cars and I'm pretty sure those same rules applies.
     
    #5 BiomedO1, Apr 10, 2025 at 10:44 AM
    Last edited: Apr 10, 2025 at 8:16 PM
  6. U A

    U A New Member

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    The replacement ecu is from a donor car that has been totaled; another Japanese import model but it is a 2017 car. The car we’re trying to fix is a 2016.

    What would be the procedure for reprogramming the engine ecu given that the diagnostic tool cannot communicate with it. I am also getting a B2279 code from the immobiliser, again to do with the fact that the engine isn’t starting.
     
    #6 U A, Apr 10, 2025 at 3:32 PM
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