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Xenon headlight issue

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by quattrov6tdi, Mar 10, 2011.

  1. V8Guzzler
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    V8Guzzler Member

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    [Apr 13, 2011]
    Same happened to me when disconnected.

    Sounds like we both have bad connections. Yours from the module to the motor, and mine from the sensor to the module..

    The big question is..

    How do you find a bad earth? Can anybody help?
    #41
  2. mike foster
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    mike foster Fossie VCDS Map User

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    [Apr 13, 2011]
    Why don't you create yourself another earth direct to the battery and see if that fixes it ?
    #42
  3. V8Guzzler
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    V8Guzzler Member

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    [Apr 13, 2011]
    Good idea, all we need know is some guidance... Knowing my luck I would blow the car up :)
    #43
  4. Woorlord
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    Woorlord shifting to Hyperspace... . VCDS Map User

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    [Apr 14, 2011]
    All Audi earth wires are coloured Brown so not really to hard to identify the wires - unless you are colour-blind maybe!!!
    As Mike says create a new one for test purposes from a good earth point like the battery negative terminal.
    To check earth wires use a reasonable quality Multimeter and set to Ohms and make some measurements from the test point with respect to the negative earth terminal of the battery, (Infinity means open circuit, small number of Ohms like 1-2 Ohms is a short circuit.)

    HOWEVER.... the level sensors do not have a direct earth on them!

    Here is the circuit on the sensors:

    [​IMG]

    How to test the G78 sensor.......

    With the system fully connected and ignition on,
    On G78 I would expect to measure a fixed voltage between G78 "5/+" [19] (positive) and G78 "1/-" [20] (negative) connections - the schematic shows the polarity which I have put in brackets. The headlight range control circuit probably has a diagnostic check to make sure this connection is made as the load is a fixed resistance.

    NOTE: J431 is the Headlight range control unit behind the glovebox - it's respective connections are shown in [brackets].

    Check this voltage at the control unit end and also the sensor connector end - voltages should be the same at both ends - or near as damn it. If not at the sensor end then there is a broken wire along the way.

    The output voltage between "4/S" [15] and "1/-" [20] will vary as per the level of the suspension at the front - maybe you can move the suspension by jacking up and down the front??

    Similarly measure the voltage at the control unit end and the sensor end with no change in suspension level - if they are the same voltage then working OK, if not then there is a break in the wiring.

    Have ago at this and feed us back your findings.
    Last edited: Apr 14, 2011
    #44
  5. V8Guzzler
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    [Apr 14, 2011]
    Thats my weekend taken care of - Many thanks to Woorlord, what would we do without you :)
    #45
  6. V8Guzzler
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    V8Guzzler Member

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    [Apr 15, 2011]
    Well, its a faulty sensor - when you take a look at the meas. blocks on ignition only it is 0v, when engine running its allover the place... Rear sensor at a steady 2.2v - new sensor should sort it then :)
    #46
  7. Woorlord
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    Woorlord shifting to Hyperspace... . VCDS Map User

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    [Apr 16, 2011]
    Can you post up the measuring block information for reference and any screen dumps - maybe useful for others.
    #47
  8. V8Guzzler
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    V8Guzzler Member

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    [Apr 16, 2011]
    Sure will do mate. Thanks for all your help on this.
    #48
  9. V8Guzzler
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    [May 4, 2011]
    Sorry for delay.. Been busy with work!

    Being fixed tomorrow at C&R ... £200!!!
    #49
  10. quattrov6tdi
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    quattrov6tdi Member

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    [Apr 22, 2013]
    Sorry for bumping this thread .....please forgive me. Two main dealer trips and two auto electrians and still no joy. Is it possible to manual adjust the headlights up for doe/nct purposes? As an aside a mate of mine put his Snap-On diag on it yesterday and couldn't access the xenon light module,might be a coincidence though.
    #50
  11. NHN
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    NHN Retrofitter - Audi - VW - Skoda - Seat Site Sponsor VCDS Map User

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    [Apr 22, 2013]
    You need to put it on vcds & then test for module 55, if its still not accessible, then this maybe why there's an issue if fuses & wiring has been checked already.
    #51
  12. s4mark
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    s4mark Member

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    [Apr 22, 2013]
    I had this exact problem on my S3. I replaced the motors and still they didnt adjust or when they did would soon drop and point to the floor, Bought 2 new genuine headlight units from audi (not cheap!) as my old ones were dull and chipped only to find they still did it! Finally solved it by changing the headlight range control unit with a second hand one for £10, fitted it myself and got the garage i use to reset the beam level with vcds. Lights were perfect and never played up after that.
    #52
  13. quattrov6tdi
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    quattrov6tdi Member

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    [Apr 25, 2013]
    No worries thanks for your reply but now I can't get my cable for vagcom to work with windows 7....I'm all problems lol
    #53
  14. quattrov6tdi
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    [Apr 25, 2013]
    Thanks again for reply I fixed my vagcom (only a fimware update, I'm so lazy). But module 55 is still inaccessible so I guess I'm back to square one again.
    #54
  15. quattrov6tdi
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    quattrov6tdi Member

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    [Apr 27, 2013]
    By the way a bit more info about my problem.I loaned the car to my Dad and he went on long journey with a serious amount of weight in the boot(arse touching the road weight) and he called me to say the issue had arose. This thing really is wrecking my head. I meant to say that is the driver's side light,the passenger one is aimed correctly abeit I don't know if it is adjusting up and down.
    Last edited: Apr 27, 2013
    #55
  16. Woorlord
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    Woorlord shifting to Hyperspace... . VCDS Map User

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    [Apr 27, 2013]
    I think this thread is pretty complete if you read all the posts - check all the wiring.
    Get a replacement control unit (located behind glove box - see previous posts for picture location) - come up on Ebay quite alot - paid a few pence couple years ago. Seen them recently for around £40.
    Check at German & Swedish - it's a Hella Part, "5LA 008 081-10", Audi Part no. "4Z7 907 357".
    #56
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  17. NHN
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    [Apr 27, 2013]
    We're going round in circles here, just do as advised, as nothing more can be said.
    #57
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  18. quattrov6tdi
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    quattrov6tdi Member

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    [Apr 27, 2013]
    Ok I ordered the module tonight cost 60 dollars delivered. Let ye know how it goes.

    Thx again guys
    Last edited: Apr 27, 2013
    #58

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