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Strange DSG starting problem - PRNDS when lights on?

Discussion in 'A3/S3/Sportback (8P Chassis)' started by audi_a3, Oct 8, 2011.

  1. audi_a3
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    audi_a3 Member

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    [Oct 8, 2011]
    2005 A3 2.0 TDI SPORT BKD DSG

    Ok I've recently developed a strange problem, if I try to start the car with the sidelights or the headlights on, it doesnt start and PRNDS flashes up on the display.

    If I turn the lights off it will start fine without a problem.

    hooked it upto VCDS and got an intermittent connection problem with transmission shift module.

    Can anyone help with this?

    and whats the connection between the lights and the gearbox?!

    thanks
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  3. jin2
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    jin2 Member

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    [Oct 11, 2011]
    Could be a battery that is not healthy, but i would guess at a grounding problem.
    Check all the grounding points (especially any for the lights) and check the grounding to the gear box.

    It might be related to the lights on the shift module, might even need to clean the connector to the shift module, but take advice on this.
    As ever disconect the battery when doing anything related to the gearbox, it's better to be safe than have a giant bill.
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  4. audi_a3
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    audi_a3 Member

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    [Oct 17, 2011]
    Sorry bout taking so long to reply, only managed to take a look at it this weekend!

    Interesting that you mention a grounding problem! I removed the airbox to take a closer look at the gearbox connections and guess what I found!

    There was a non-standard cable fitted from the top of the gearbox to the battery grounding post. (Ill post a pic) The cable used was some 8 gauge speaker cable!!
    I removed the cable and tried to start the car and it didnt start, didnt even try to crank,

    Fitted it back in and it started, but still got the same PRNDS when I try to start it with the lights on?

    So I guess there is a problem with grounding somewhere then. The standard grounding cable is still fitted to the gearbox and connects to the chassis, but I guess its not doing its job?!
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  5. paddy
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    paddy Audi=No fault code, no idea

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    [Oct 17, 2011]
    Try just running a jump lead from the box to the earth/chassis.
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  6. audi_a3
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  7. NHN
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    NHN Retrofitter - Audi - VW - Skoda - Seat Site Sponsor VCDS Map User

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    [Oct 18, 2011]
    Remove all ground wires, clean the stock cable with some fine sand paper, these are known to become non conductive & the coating on the bare metal becomes (cant think of the word atm) but crappy, hence affecting conductivity, clean contacts up on the terminals connecting to on the chassis, gearbox & starter, see if that helps.

    I've read about this issue before & I've personally done this to my cars to create better connectivity, wont make it any worse thats for sure lol.
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  8. mike foster
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    mike foster Fossie VCDS Map User

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    [Oct 18, 2011]
    Are you looking for 'oxidised' by any chance ??? lol
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  9. jin2
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    jin2 Member

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    [Oct 18, 2011]
    Hmm, interesting looking ground wire you have there.
    When cleaning the grounds on my car I used a wire brush and cleaned the post in the car, the nut and the connector/ terminal on the end of the wire.
    After cleaning I put a thin smear of grease on the post, connector/ terminal and the nut. (to help prevent this happening again)

    If you have access to a multimeter, check for a connection between the gear box and negative of the battery, after you have cleaned all the ground points.
    I recon the current connection is not making or is high resistance and confusing the gearbox ecu.
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  10. audi_a3
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    [Oct 18, 2011]
    Thanks Chaps.
    Interesting. When I had a look at the weekend I removed all the ground cables, and cleaned all the corrosion off with a combination of wd-40, wire brush and sand paper. Cleaned the point on the gearbox terminal, the chassis ground point, and both ends of the standard grounding cable back to bare metal. Finished off with some electrical contact cleaner and copper grease before refitting everything.

    I also took the starter motor off aswell to clean all its terminals too as I've got a hard starting problem, and looking back now I noticed something...

    I used to have a manual version of the same car before this, and the starter motor on that car had a ground cable attached to one of the big bolts which holds the starter to the gearbox.... the starter on this DSG version doesn't have that ground cable there though.

    Im assuming the starter on the DSG is grounded through that grounding point on the DSG box?

    Found a pic of the manual version here http://www.myturbodiesel.com/1000q/a5/starter-removal-Jetta-mk5.htm
    [​IMG]

    The connection at the blue arrow isnt present on my DSG. That connection on my DSG starts at the same place (ground point on the right of the yellow arrow) but connects to my gearbox instead of the starter. Is that how its meant to be on the DSGs??


    If that connection is right, then I guess theres a problem with that standard grounding cable as it still didnt work even after I cleaned up all the terminals?
    It is also possible for that grounding point in the engine bay to be damaged and not actually touching the grounded chassis, which seems unlikely?
    If that speaker cable has taken over full responsibility of grounding the g'box and starter, then I guess you could be right in saying that there's higher resistance present messing things up as that speaker cable doesnt look as thick and is probably not as good quality as the standard item, plus about 4 times longer!

    Will have to get a multimeter on it soon to figure out what values im getting where.
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  11. jin2
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    jin2 Member

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    [Oct 19, 2011]
    An interesting question, hopefully some one can answer that question for you.

    I think you are dead on with your thoughts about the speaker wire, if you have a multimeter then check the ground from the gearbox to the car, then check the resistance, if its low then its good (would be interesting to see what the resistance of the speaker cable is).
    You could also check for an electrical connection using the multimeter from the gearbox / engine to the chassis.

    If you remove the speaker cable does the anything happen when you try and start the car ? (light, fans, clicking, anything ?), if not then I suppose it is possible that there is no ground going to the engine :ohmy:
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  12. audi_a3
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    [Nov 27, 2011]
    Finally got round to root causing this! Had another gander at the OEM black ground wire between 'box and the chassis.... and noticed it had corroded all the way through under the plastic sheathing! i.e. where the wire is crimped to the connector. I pulled on the cable and it came off leaving the connector still on the car! There was nothing left holding it together.

    Ill buy a new one this week, but in the mean time i connected that speaker cable to the original gearbox grounding location (under the battery) and it seems to have fixed my original problem. I can now start the car with the lights on! Wahay!
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  13. fangio
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    fangio Well-Known Member

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    [Nov 27, 2011]
    Well done! Looks like a previous owner had the same problem and didn't repair it properly. :ermm:
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