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TD5 BCU wiring

Discussion in 'Land Rover Discovery' started by ddaann88, Jul 23, 2019.

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  1. ddaann88

    ddaann88 Member

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    Hello
    Im currently building an off road buggy, i decided to put the disco td5 auto engine and box in it, i went through all the wiring and cut everything out i didn't need to simplify it.
    The only ecu's im left with are the engine and transmission, everything works like i want it to apart from it automatically changing up gears which im guessing is because i stupidly cut out the bcu :/ is it possible to do some wiring to bypass it, or will it be a new loom and ecu. ive looked up the wiring diagrams but obviosly doesn't tell you what the power is.
    any help would be great Thanks:)
     
  2. sierrafery

    sierrafery Well-Known Member

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    Hi. I might be able to help but i dont understand what you did untill now and why are you blaming the BCU only? did you completely rewire the CAN bus and all other inputs between the ECM and autobox ECU? ... the BCU is there only for the ''autographics"/ warning light management, it has not much to do with shift control
     
  3. gstuart

    gstuart D3 Grandad

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  4. ddaann88

    ddaann88 Member

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    Thanks for the help couldn't find what i needed on the links as im unsure on which ones are needed. Ive basically just cut the wiring out that i thought was not needed and left the original there and just lengthened various wires that i needed, it has had the immobilizer removed.
    only reason i thought it was ecm as looking through the wiring there are i think there are 3 wires that go to the gear selector i know one of which has a 12 feed which ive wired up, i just though maby its to do with this as i am also getting an error for position switch monitoring. thanks
     
  5. sierrafery

    sierrafery Well-Known Member

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    I hope that at least you can understand tgis phrase you wrote cos i\m stumped :confused:
     
  6. ddaann88

    ddaann88 Member

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    hah let me try again i blame dyslexia;) the only wiring on the car that are not original land rover wires are an extension loom (red ecm plug) and a few wires i had to extend from the engine, i haven't touched can network.
     
  7. sierrafery

    sierrafery Well-Known Member

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    AAA-Haaaa .... IMO that's the problem cos even though they advertise those extensions as being for Discovery 2 too not just defenders they missed to say that it is valid only for manual models cos it's completely missing the CAN circuit. So as long as you have that extension loom the autobox will not work ... see post 3 https://www.landyzone.co.uk/land-rover/d2-td5-loom-extension-issues.308892/
     
  8. ddaann88

    ddaann88 Member

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    right ok i did actually have someone make it up for me not sure how he wired it though, il have to give it a go as it was
     
  9. ddaann88

    ddaann88 Member

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    still no luck unfortunately, on the bcu wiring diagrams it show 3 wires going out to the selector do you think this could have something to do with it or would those wires go to the dash or something like that
     
  10. sierrafery

    sierrafery Well-Known Member

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    So ca you confirm 100% that the CAN wiring is there? ..... untill this thing is nit ruled out any other discussion is futile
     
  11. ddaann88

    ddaann88 Member

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    yes CAN wiring is all there
     
  12. gstuart

    gstuart D3 Grandad

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  13. sierrafery

    sierrafery Well-Known Member

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    The most important is the feed for the XYZ switch from BCU C0663-10 so make sure that the switch gets this feed
     
  14. gstuart

    gstuart D3 Grandad

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    Spooky as I had just past a picture of the 663 connector, well over my head but know ur the wizard when it comes to this

    F379AA0E-40AC-4563-A796-072E4AA674CA.jpeg
     
  15. sierrafery

    sierrafery Well-Known Member

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    Important is to measure for 12V across body and C0675 - 8 with ignition on cos if that's missing that's the culprit

    C0675.jpg
     
  16. ddaann88

    ddaann88 Member

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    thats all for the suggestions, ive wired up that C0675 no.8 wire to 12v live feed but fault is still there, ive tested all the out puts from the xyz switch whilst shifting through the gears with multimeter and all seems to be correct including the earth. any other ideas
     
  17. sierrafery

    sierrafery Well-Known Member

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    IMO another problem caused by
    is that the management misses the VSS delivered by the SLABS ECU which you dont have and while the egine management is mixed up the shift control will not work as well .... though the direct way to the fault would be to wire up the OBD link and read the fault code which causes the limp mode, the EAT management is very complex, if it misses vital inputs it will not work well... how would the autobox ECU manage the gears as long as it doesnt know the vehicle's speed?

    VSS description.jpg
     
    Last edited: Jul 26, 2019
  18. Stanleysteamer

    Stanleysteamer Well-Known Member Full Member

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    Bet you're wishing you fitted a clutch and manual box!
     
  19. ddaann88

    ddaann88 Member

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    haha sometimes;) cheers for help got it working eventually, i think it was pin 5 out of the selector but re wired them all and now works great:)
     
  20. Stanleysteamer

    Stanleysteamer Well-Known Member Full Member

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    Building a special with an TD5 engine and autobox, you are a braver man than me!
    WELL DONE!!!
     
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