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Thread: No power to the ECU

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  1. No power to the ECU 
    #1
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    My 2011 2.0 TDI come to a stop and VCDS said it could not talk to the ECU and it had a clutch switch fault (short to positive). The garage replaced the switch and the ECU was still a no go. They found that if they forced a conenction from the ecu relay the ecu powered up and all was well. They then said that the ECU itself is responsible for switching the relay and it wasnt doing that. They said they tested the relay too. So i send the ECU away and got a refurbished one reprogramed from my old one and the problem is still there. They say the ECU is not earthing out the switch in the relay so the ECU is not fully powering up. Theyve checked all the wiring they think is involved and found nothing wrong.

    Does anyone have any ideas as im bloody lost here.

    Thanks

    Jon
     
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  2. Re: No power to the ECU 
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    how can the ecu power up the relay that powers it up.. ?? i would try a new relay myself first off. that will be powered from the ignition switch, so could be that, but i would need to study a wiring diagram to suss it out properly, which is what the garage should have done.
    Audi 80 tdi avant with 360,000 miles...
     
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  3. Re: No power to the ECU 
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    This is what the garage is telling me that VW work differently and the ecu earths out a positive to the relay to juice up the relay. Low voltage switch I guess
     
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  4. Re: No power to the ECU 
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    so with no power the ecu earths out a relay to swicth itself on. hmm, righto..
    Audi 80 tdi avant with 360,000 miles...
     
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  5. Re: No power to the ECU 
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    has anyone done a full fuse check just in case the clutch switch has blown one ? unfortunately i don't have a wiring diagram so can't check for you, but when you tun the ignition on that will power the ecu relay which then fires up the ecu.
    Audi 80 tdi avant with 360,000 miles...
     
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  6. Re: No power to the ECU 
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    Strange isn't it but it's what the garage tell me. I wish it was the relay
     
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  7. Re: No power to the ECU 
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    well find another garage then.
    Audi 80 tdi avant with 360,000 miles...
     
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  8. Re: No power to the ECU 
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    I checked as many as I could but had no map to go from. Not sure what's been done since. Would a broken fuse mean that the car wouldn't start with the wire instead of the relay? I guess so if the garage didn't get the right feed from the ignition.
     
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  9. Re: No power to the ECU 
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    The company you sent the ECU to, are they located in Heanor?

    I will assume the engine is a CFFB code without stop start.

    The engine ECU has a main power feed called Line 87a from fuse SB14 in the engine bay fuse box (called SB) which splits into three separate feeds to the ECU. Fuse SB14 gets its power from the Line 30 J317 relay at position A2 on the fuse box and this gets its power from a connection on the front of the under bonnet fuse box which is direct to battery. Is this the relay they are jumping across? This relay gets its trigger side power feed from fuse SB13 and this is also the permanent Line 30 power feed to the ECU for memory saving purposes, the wire is only 0.5-mm core. The slightly obtuse point is this relay is earth triggered by the ECU which it is powering so it has to be powered up first to be able to do this by an ignition on feed from the Line 15 relay via fuse SC10 in the dash side fuse box, this relay is under the dash at position 2 on relay carrier 3 and has the number 645 printed on top, so is this the relay they are jumping across?
    Dark was that day when Diesel conceived his grim engine that begot you, vile invention, more vicious, more criminal than the camera even, metallic monstrosity, bale and bane of our culture, chief woe of our Commonweal. How dare the Law prohibit hashish and heroin yet license your use, who inflate all weak inferior egos? Their addicts only do harm to their own lives: you poison the lungs of the innocent, your din dithers the peaceful, and on choked roads hundreds must daily die by chance-medley. Nimble technicians, surely you should hang your heads in shame. Your wit works mighty wonders, has landed men on the Moon, replaced brains by computers, and can smithy a "smart" bomb. It is a crying scandal that you cannot take the time or be bothered to build us, what sanity knows we need, an odorless and noiseless staid little electric brougham.

    W.H. Auden (1907-1973), A Curse:
     
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  10. Re: No power to the ECU 
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    Wow thanks so much for such a detailed reply. The relay they are bypassing is the one under the bonnet marked 370 8d0951253.

    The garage is convinced it's the Ecu and still the Ecu (refurbed one) as the Ecu is not earthing out the feed to the relay. The Ecu people asked for it back to test it again but to be honest I'm loosing confidence in the garage as I think they and the Ecu people have different schematics. I don't even have a fuse map for the car (does anyone have one). The chats between the garage and the ecu people found that there is feed from the ignition to the ecu when the key is in. Despite them having different points to test that from their documents

    thanks again a in for your help

    oh the engine code is cffb but it does have stop start.
     
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