Immobiliser Problems

Discussion in 'Prius v Main Forum' started by dy/dx, Jan 3, 2026 at 5:04 PM.

  1. dy/dx

    dy/dx Junior Member

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    I have a specific problem I can't get my head around. I bought a 2016 Prius V. After replacing the keyfob battery, I discovered these:
    1. If I press the start button, nothing happens. It doesn't beep to tell me there is no keyfob, it also doesn't recognise the keyfob. Same thing happens if the keyfob is outside the car.
    2. The keyless entry on the driver's door does not work. If I grab the handle, the door does not open, if I touch the lines, the door does not lock.
    3. The door opens or locks if I use the buttons on the keyfob. The alarm button also work.
    4. I can start the car if I touch the keyfob logo on the start button. However, if I open the door while the engine is running, it doesn't prompt me for the keyfob.
    5. When I connected Techstream to the car, it shows a different VIN number. I assume a specific ECU was replaced before purchase?
    6. I programmed another keyfob, but it behaves exactly like the other keyfob.
    Please see the data list attached.
    Kindly help me out with a solution.
     

    Attached Files:

  2. Air_Boss

    Air_Boss Senior Member

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    I know nothing about this issue in the Prius (had it occur in the Honda), but I note in your scan page ‘Master Key = Match’ and ‘Sub Key = No Match’ and ‘Number of Registered Key Codes 5’, and wonder whether those plus the ECU mismatch are important hints.
     
  3. Brian1954

    Brian1954 Senior Member

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    ^1
    I also see that # Codes=1. Did you do a Health Check to look for codes the car is reporting?
     
  4. dy/dx

    dy/dx Junior Member

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    Yes, B2799.
     
    #4 dy/dx, Jan 3, 2026 at 9:14 PM
    Last edited: Jan 3, 2026 at 10:22 PM
  5. Brian1954

    Brian1954 Senior Member

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    Do you mean B2799?

    Is that the only code the car has?

    Did you use a meter to read the voltage of the new battery that you installed into the fob?
     
    #5 Brian1954, Jan 3, 2026 at 9:33 PM
    Last edited: Jan 3, 2026 at 10:10 PM
  6. dy/dx

    dy/dx Junior Member

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    You are correct, B2799.
    That's the only code.
    I didn't, but I programmed a known working keyfob from another PriusV and it has the same behavior.
     
  7. Brian1954

    Brian1954 Senior Member

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    Thanks for the reply.

    I did a search. It appears that the problem is because of the different ECU that was installed into the car. Take a look at this post by @ChapmanF,, https://priuschat.com/index.php?posts/3038930

    Look at the freeze frame data for the P2799 code for the INF detail code. That may help narrow down the problem.
     
    #7 Brian1954, Jan 3, 2026 at 10:59 PM
    Last edited: Jan 3, 2026 at 11:34 PM
  8. dy/dx

    dy/dx Junior Member

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    I just checked again, it seems B2779 is correct.
     

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  9. Brian1954

    Brian1954 Senior Member

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    Okay, disregard the link that I provided in post #7. This could still be related to the ECU mismatch.

    Did the key fob work properly before you replaced the battery?

    I did some searching and found the following information.
    Code B2779 Toyota Description
    When an internal malfunction occurs in the Certification ECU (Smart Key ECU Assembly), the Certification ECU (Smart Key ECU Assembly) stores this Diagnostic Trouble Code (DTC).
    [​IMG]
    B2779 Toyota Code - Engine Starter Communication Malfunction

    What are the Possible Causes of the DTC B2779?
    • Faulty Certification ECU (Smart Key ECU Assembly)
    • Certification ECU harness is open or shorted
    • Certification ECU circuit poor electrical connection
    I would try to determine if the remote start is OEM or aftermarket. If it is an aftermarket kit, I would remove it from the car.
     
    #9 Brian1954, Jan 4, 2026 at 10:24 AM
    Last edited: Jan 4, 2026 at 10:36 AM
  10. dy/dx

    dy/dx Junior Member

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    How do I determine that?
     
  11. Brian1954

    Brian1954 Senior Member

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    I think it would be installed near the OBD2 port. I have no experience with these systems.

    Each manufacturer of these kit will be a little different. I did a quick search and found this website for 12volt.Solutions. Scroll down to the video at the bottom of the page. Here is a more detail installation video,
    . You can do a search for other companies that make these remote start system for more information.

    Here is a more detailed video from another manufacturer. PRIUS9 – Start-X

    FYI, I edited post #9 a little.
     
    #11 Brian1954, Jan 4, 2026 at 10:50 AM
    Last edited: Jan 4, 2026 at 11:08 AM
  12. dy/dx

    dy/dx Junior Member

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    I have searched thoroughly, but I was unable to locate any installed remote start system. Additionally, pressing the lock button three times does not initiate the vehicle.