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`left dipped headlight` but bulb and fuse are okay

Discussion in 'A3/S3/Sportback (8P Chassis)' started by synthdood, Nov 14, 2010.

  1. synthdood
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    synthdood Member

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    My 2005 A3 8p with normal halogen bulbs has the left headlight not working since today. The DIS shows the `left dipped headlight` error. When I went to replace the bulb I dicovered that there was nothing wrong with it. I checked the fuse and that is also okay. I tried disabling the cold diagnosis with VAGCOM thinking that maybe a faulty measurement that was causing the problem, but unfortunately that didn´t help.

    Is there anything else I can look at besides bulb and fuse? Maybe a relais?
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  2. mike foster
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    mike foster Fossie

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    Have you done a full fault scan to see what that says ?

    How do you know there is nothing wrong with the bub ? Did you try substituting it in the other side ?

    Finally, if you have any test equipment try and see if there is the correct voltage present on the bulb connector.

    Just because a bulb looks ok does not mean it is ok !
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  3. synthdood
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    synthdood Member

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    The VAGCOM fault scan says that there is an open connection or a short on the left headlight.
    I replaced the bulb with a new one (that I measured so I know for a fact the new one is okay) but that didn't help. I measured the voltage on the bulb, that was 0.3V (I am guessing this is the measuring voltage of the colld diagnosis system). There is 12V on both sides of the fuse so I know the fuse is okay. It looks as if the voltage from the fuse is never reaching the headlights. Just to be sure I also switched the fuses for the left and right headlight. That didn't help.


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  4. jimmy77
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    jimmy77 Member

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    hi mate i had this problem a few weeks ago with a customers car, same fault as you and i tried everything to get it working with vagcom and a very clued up mate on audi's and vw's, i ended up taking it to audi and it was the lighting control unit!! they are a common problem on the 8p apparently, the bad news is that it cost around £450 to get it fixed!!!
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  5. mike foster
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    mike foster Fossie

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    Sometimes the ecu's get locked up like any other computer.

    Might be worth disconnecting the battery for half an hour or so to see if it resets itself. As far as a 'common problem on A3's ' is concerned I haven't seen any other threads on here about the problem.

    Do a search on here to see if there is anything about it.

    Sorry can't be more help

    Good luck
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  6. synthdood
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    synthdood Member

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    I seen very similar problems pop up many times in US forums but those always appear to occur with xenons. In fact a class action lawsuit is being filed against audi for those cases because eventhough Audi are aware of the recurring issue they keep charging customers for (very expensive!) repairs where they completely replace the HIDs and these repairs do not appear fix the problem.

    I don't have xenon though, just the normal H7 halogens. I think I will take the car to audi next week and see what they come up with. Let's hope it is not going to be expensive.
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  7. synthdood
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    synthdood Member

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    So I took the car to Audi this morning. They changed the bulb and all was fine. You have no idea how stupid I feel right now (I have a degree in electronics for f** sake).

    The question remains, why was there no 12V when I measured in the first place? And why didn't it work when I replaced the bulb? The only thing I can think of is that I should have switched the car off and on after replacing the bulb. I tried replacing it while the lights were switched on in order to see if the new bulb worked. Maybe the car refuses to supply 12V after sensing something is wrong and it needs a restart? Lesson learned for next time: Replace bulb while the car is off and test afterward!
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  8. mike foster
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    mike foster Fossie

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    :laugh: - sometimes we can't see the wood for trees !!

    Glad you got it sorted.
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  9. PH1L
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    PH1L Gievf Buckets

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    when the can line sees what it percieves to be no bulb it shuts off power to the line
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  10. NHN
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    NHN Modmetractor

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    Nah I reckon it just wanted to wind you up on that day for not being nice to it, A3's need some love & attention you know, a gentle rush of the dash with care & love does the trick lmfao
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  11. PH1L
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    PH1L Gievf Buckets

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    haha nige is soo right treating the a3 mean doesnt keep it keen!
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