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Re-setting ECU After Battery Disconnected?

Discussion in 'A4/S4 forum(B5 Chassis)' started by Siena, Jan 30, 2008.

  1. Siena
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    Siena Active Member

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    [Jan 30, 2008]
    Hi guys, my car has had the battery disconnected for a while - about 2 weeks completely dead, and about 2 days off the car, whilst being charged.

    Now, it starts ok, but runs at about 1,500rpm for the first 40 seconds or so, then ocillates up and down between 800 and 1,500rpm thereafter. It doesn't pull strongly either at low speeds.

    Is there any way besides VAG-com, to do a hard re-set? It's a 1996 2.6, ABC code.

    Thanks.
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  3. mwarrey
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    mwarrey Member

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    [Jan 30, 2008]
    Are you sure its the battery? Worth checking to see if there are any pipes\ connections that are not on properly. Did the body shop move anything when they were painting the wings ?

    Similar thing happened to me after a full respray, it was a loose breather pipe (on a golf though)
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  4. Siena
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    Siena Active Member

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    [Jan 30, 2008]
    Hmm, checked all pipes yesterday, the only pipes that could have been disturbed, would have been the pipes to the charcoal canister (o/s front). But they're all intact.

    Pulled fault codes, and the only one that comes up is "Engine control unit blocked". Also spoke to a couple of people, and the first asked me if the battery was disconnected recently. They both seem to be of the opinion the ECU needs basic re-set. I've also been told there's a manual procedure of doing it, but not sure how!
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  5. FactionOne
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    FactionOne Well-Known Member

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    [Jan 30, 2008]
    I'd be inclined to agree...

    When you have the battery disconnected for a while the only real thing 'engine-wise' that the car forgets is the throttle-body alignment. If you can get to VAG-COM, you need to open the engine module go to measured value block 98 (or 60 for DBW) and hit 'switch to basic settings' then just wait a few seconds. If you can't get to VAG-COM though, the car should actually sort itself out - when you turn the ignition on for the first time leave it without starting the engine for 20-30 seconds and then start it and let it run at idle for 20-30 seconds. If it's still ropey after that it's more likely you've got pipework/cabling out of place (or possibly of course a fault somewhere - but given it's been nowhere and done nothing for a while, I guess that's least likely)

    Regards,

    Rob.
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  6. Siena
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    Siena Active Member

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    [Jan 30, 2008]
    Cheers, Rob. Will give it a try.
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  7. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Jan 30, 2008]
    It also takes a while for the ECU to relearn everything if it's been disconnected. A couple of hours driving should improve it.
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  8. macca
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    macca Member

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    [Jan 30, 2008]
    agree with andy mac, i think the ecu may adjust to the fuel you use, when you disconnect battery it resets. mine seems to need a while to get back to smooth running again, though i wouldn't expect to see the idle go up and down a lot unless there is an air leak.
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  9. Siena
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    Siena Active Member

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    [Jan 30, 2008]
    Thanks for your suggestions, folk. I ended up using a Snap-On scanner to revert the ECU / throttle body / idle speed actuator to basic settings, took less than 5 minutes, and she's back to normal.

    Thanks anyway!
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