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Defeated ECU’s ??

Discussion in 'A3/S3 Forum (8L Chassis)' started by A3 T, Nov 5, 2013.

  1. A3 T
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    A3 T Lord Of The Rings

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    [Nov 5, 2013]
    Hi guys


    Its looking like i may need to replace my ECU :(

    I've seen a few ECU’s for sale saying that they are immobiliser defeated so they are plug and play.


    What I'm wondering is what happens about the dash as when you turn on the ignition, wouldn't the immobiliser part in the dash try and communicate with the ECU and when it doesn't find the immobiliser part in the ecu stop the car from starting?


    Or am i way off...lol
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  3. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Nov 5, 2013]
    Immo defeat just turns the immobiliser off essentially but the new ECU can be re-coded if required... personally I would prefer to retain the immobiliser

    There is no issues with the dash and no lights stay on with immo defeat

    <tuffty/>
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  4. @udi A3
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    @udi A3 Site Sponsor Site Sponsor VCDS Map User

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    [Nov 5, 2013]
    where abouts are you? Ecu swaps are something I can do quite easily the correct way. Immo defeat I only really do to diagnose issues.
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  5. A3 T
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    A3 T Lord Of The Rings

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    [Nov 5, 2013]


    Thanks for that tuffty mate ;)

    I've always thought that the immobiliser part of the car was split into two and so when you turn the key, the key chip would need to sync with half the immobiliser in the ecu and half in the cluster.


    From what your saying its more like the car has two immobilisers (one in the ecu and one in the cluster) that are synced together ?



    Thanks mate ;)

    But I'm in london so a bit far from you.

    I've heard its easy enough to program it in using vag can commander 1.5 but I've also read some horror stories....lol
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  6. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Nov 5, 2013]
    The immobiliser is in the cluster, and tells the ECU its allowed to start the engine if the key is valid.

    So key is synced with cluster, and then cluster is paired up with the ECU.
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  7. A3 T
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    A3 T Lord Of The Rings

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    [Nov 5, 2013]
    Oh ok.

    Wouldn't that then mean that immobiliser would still be effective even with a ecu defeat, as if you tried to start the car without the key then the cluster wouldn't tell the ecu to start?
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  8. RobinJI
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    RobinJI Member

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    [Nov 5, 2013]
    With the immobiliser defeated, the ECU won't care what clocks are connected to it, the clocks don't even have to be there. It's the ignition switch that tells the engine to start not the clocks, and the ECU reacts accordingly by checking with the clocks whether it's meant to be running or not. With the immobiliser defeated, it just doesn't bother checking.
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  9. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Nov 5, 2013]
    exactly. With it defeated the Cluster could say "DO NOT START" or even nothing at all, and the ECU would ignore it and allow the engine to start anyway.
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  10. A3 T
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    A3 T Lord Of The Rings

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    [Nov 5, 2013]
    Thanks mate I get it now ;)

    if I get one without the defeat is it easy enough to get it to work using the cheap vag can commander / leads ?
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