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Help request: Main Body ECU schematic?

Discussion in 'Gen 3 Prius Technical Discussion' started by Roccobro, May 11, 2024.

  1. Roccobro

    Roccobro Junior Member

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    Chasing down a power window issue and have multiple spare parts that have all failed to fix the problem. Alldata says the main body ECU should have 1 or less ohms between gateway computer pin #16 and Body ECU #27 [2A-27 (LIN2) - MB-16 (LIN2)] and 10 kΩ or higher From 2A #27 [2A-27 (LIN2)- Body ground].

    My spare ECUs and master window switches don't fix the issue. Now I NEED to verify at a board level component failure so I don't keep chasing my tail.

    I couldn't find it online or on Alldata (its being really slow on my home PC). Does anyone have access or able to provide a schematic for the Body ECU for a 2012 regular Prius 3? I have one opened up and made cutouts where I can, but I can't follow the traces under some plastic I cannot remove.

    THANKS!!

    Justin
     

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  2. ChapmanF

    ChapmanF Senior Member

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    What readings did you get?

    The "inner circuit" of the junction block that the body ECU sits in is published in the Electrical Wiring Diagram. That's enough to see the LIN connections between the external pins 2A-27 and 2D-26 and the pin 16 of the body ECU itself. That's the continuity that Toyota is having you test.

    Toyota Service Information and Where To Find It | PriusChat

    The schematic of the body ECU itself isn't published that I know of. You'd probably have to be their supplier, and maybe sign an NDA.
     
  3. Roccobro

    Roccobro Junior Member

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    Thank you Chapman. I got 2.5-4k ohms so its out of spec. But swapping in another board (admittedly unknown from wrecked car) gives same results. Even a combination of the donor and original gateway ECU and original and donor Body module gives same results.

    I'm getting power to the master window switch at LIN and power (B), ground is good through switch. The "output" pink line from Switch to body ECU fluctuates in voltage. Master window switch is known good from my personal driver car.

    Im a simple person when it comes to current flow. I'm wondering if one of the board mounted relays is shorted or faulty. Without further direction without a schematic is I will rig up my relay tester to micro connectors and test every single relay while its still attached to the board. (Yes, that is not ideal in component testing).
     
  4. ChapmanF

    ChapmanF Senior Member

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    The "inner circuit" diagram doesn't show anything special on that path connecting 2A-27 and 2D-26 and pin 16 of the body ECU connector. Just copper.

    The diagram, of course, is not showing any of the ECU itself. This path is part of the junction block that the ECU attaches to.

    It might be unclear just what "board" you have swapped. Swapping the body ECU would not be expected to correct a weird reading on this test.

    Alldata seems to be changing the names of some things, which probably doesn't help make anything clear. "Gateway ECU", to my knowledge, isn't a thing in a gen 3 Prius (gen 1 and gen 2 had one). The connection being tested here is between the body ECU's pin 16 and external pins 2A-27 and 2D-26 of the instrument panel junction block. From Those external pins it runs eventually to the driver's door master switch and to the window regulators in the other doors (and to the sliding roof control ECU, in cars with that).
     
  5. Roccobro

    Roccobro Junior Member

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    I have to clarify. Its 2A Pin #27 to ground that I get too low a reading. The "gateway" ECU is the black pancake module that snaps to the Main Body ECU.

    Alldata has what all the wires from the body ECU are for (Canada only model), but not the internal circuits.
     

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  6. ChapmanF

    ChapmanF Senior Member

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    I'll clarify back atcha. Alldata has screwed up some names compared to the Toyota manuals. The snapped-on pancake is the Body ECU, and the thing it is snapped onto is the Instrument Panel Junction Block. There is no "gateway ECU." (If you were working on a gen 1 or gen 2 Prius, there would be one.)

    This is kind of frustrating, because Alldata is mentioned on our wiki page as one of the alternative sources for repair information, but that kind of implies they'll be giving equivalent service information and not getting the names of things wrong. Phooey.

    Assuming you have a low reading on 2A-27 to ground when the ECU is unsnapped from the junction block, something in the junction block is conducting between that circuit and ground. Could some cola have been spilled in the block, or something like that?
     
  7. rjparker

    rjparker Tu Humilde Sirviente

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    Start with a better description of the problem.

    1. Do all windows fail to function?

    2. If just one is broken, which one?

    3. If it is not the drivers window, is the failure at the door and at the master drivers control?
     
  8. Roccobro

    Roccobro Junior Member

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    Anything is possible. But for two clean looking computers to have the same abnormal reading I was thinking its a connection somewhere. Either on board or in a traceable wire route. Others with similar problems have seemed to have moisture in the air as a relatable secondary factor when their cars exhibited same symptoms (no power locks, no master window kill switch function, only drivers window actuation- from the master window switch, other door switches working their respective windows). So a *higher* resistance on a line would be corroborating of moisture being a factor... But not lower resistance from ECU to ground on a circuit intended for LIN communication.

    Justin
     
  9. Roccobro

    Roccobro Junior Member

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    1. No. All work, but only from their respective switches. Master switch at drivers side has no functions other than drivers window up and down.

    2. none are window regulator related

    Edited to add: Power and grounds to the master switch and through it are getting readings. Not correct or consistent on the LIN side. Known good masters are not changing any of the functionality.
     
  10. rjparker

    rjparker Tu Humilde Sirviente

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    A quick and easy test with Techstream or another bi-directional scanner is to command each from the scanner. Then you know the body ecu is good and likely some parts of the Lin bus line are good.

    Of course the same Lin bus line goes to all doors and there are two leading to the body ecu pin 16.

    I would certainly verify the master switch pin 17 pink has continuity to the body ecu pin 16.

    IMG_5047.jpeg IMG_5048.jpeg IMG_5046.jpeg
     
  11. Roccobro

    Roccobro Junior Member

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    Techstream says no comms with any window or ECU

    I checks continuity and it was good (as far as wire connections). The line voltage pulses so its getting *something* to and from ECU to switch and back.
     
  12. ChapmanF

    ChapmanF Senior Member

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    Yes, assuming you made the test described in the manual, 2A-27 to body ground with the junction block unplugged from the wire harnesses, and the Body ECU unplugged from the junction block, then your leaky ohms reading has isolated a problem to the junction block itself.

    One unwelcome effect of Alldata messing the names up might be some mystery about how many computers are in the picture. The Body ECU (the pancake that unsnaps from the junction block) really is an ECU, the brains of the operation. Unplug that from the junction block, and what's left is not a computer or an ECU at all. There's nothing else in the Instrument Panel Junction Block any fancier than some fuses, some relays (occasionally with a snubber resistor across the coil), and circuit junctions. A lot of junctions. That's it.
     
  13. rjparker

    rjparker Tu Humilde Sirviente

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    No comm to the body ecu?
     
  14. Roccobro

    Roccobro Junior Member

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    Kind of. It will pull up the B codes (5 of them) that relate to "lost comm with DR/LR/RR/etc door" but also when I try to talk w the gateway is says it cannot communicate. I'll have to fiddle with that but nice person-umed it was a peasant with a Win95 laptop and Teschstream 18.xxx.18

    Maybe looks like in my picture above? lol Taking the part pictures from online forums as calling it "main body ECU" (like I was doing) is WORNG WRONG WRONG. Toyota parts reference pictures confirm what you are saying that it is just the junction box!

    The black pancake computer is labeled "Computer multiplex network body".

    So you are correct also that it is a failure in the junction box circuitry. Should I update the title to reflect that is the diagram I am looking for now? :p

    Thank you guys!

    Justin
     
  15. ChapmanF

    ChapmanF Senior Member

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    You're looking for the "instrument panel junction block inner circuit" diagram, which is in section F of the Electrical Wiring Diagram ... and continues over five pages, but everything there is to know about LIN2 is on the first page, and pretty boring ... nothing that hasn't already been said:

    [​IMG]
     

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  16. ChapmanF

    ChapmanF Senior Member

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    What is this gateway of which you speak?

    I had said a gen 3 hasn't got a gateway ECU the way gen 1 and gen 2 had. I might not be strictly right about it having nothing called 'gateway', because some images of Techstream's System Select show two things called PM1 Gateway and PM2 Gateway ... but still, these seem to be deep mysteries of the way the Power Management Control ECU is built, and nothing to do with the Body ECU or (probably) with your issue.
     
  17. Roccobro

    Roccobro Junior Member

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    I apologize for using that term. It was under body tab of techstream, Utility section. Only 3 options and it was the first one. I do not recall the title of the Utility action. I'm thinking I've messed up terms too bad to redeem anything I've said prior to the last few hours of understanding.

    Now that I admit I'm pretty un-smart, uh, where can I view section F of the Electrical Wiring Diagram? :notworthy:
     
  18. ChapmanF

    ChapmanF Senior Member

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  19. rjparker

    rjparker Tu Humilde Sirviente

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    I expect you have checked the fuses related to the junction block and ecu?
    IMG_5057.jpeg

    Can Techstream Read Power Window or Main Body Status and Control?
    You can’t communicate to the main body ecu or the individual power windows?

    —————————————

    Here are some screenshots:

    techstream system select 1.jpeg
    All devices above are communicating except for those with an * which don’t exist.


    Passenger power window 2.jpeg
    Passenger power window data list


    passenger p window up down 3.jpeg
    Only one active test


    main body active test 4.jpeg
    Main Body Data List and Active Tests. Door lock is an easy test to verify.

    ———————————————

    With no apparently window control from Techstream or from the driver door, I would consider isolating the Lin bus by unplugging one door at a time and retest. Both rear and the passenger door’s lin bus connects to the window regulator assembly, not their switch assembly. All four doors end up on pin 16 of the main body ecu so they are all connected.

    Post 15. As stated previously the schematic of the body ecu is not available to anyone. So all we know is the door Lin bus goes to the body ecu.

    The relays in the junction block are primarily driven by outputs of the main body ecu.
     

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    #19 rjparker, May 12, 2024
    Last edited: May 12, 2024
  20. ChapmanF

    ChapmanF Senior Member

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    ... and if the OP has measured a < 10 kΩ resistance to ground on that path inside the junction block, with the Body ECU removed and connectors 2A and 2D unplugged, then there really is something conducting to ground on that trivial path connecting those three junction-block pins, as seen on the right of the diagram in post #15.