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W212 2012 model, left Xenon lamp out (not the Bulb or wiring)

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by PaulOD, Nov 14, 2020.

  1. PaulOD

    PaulOD Member

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    Hi Folks

    New issue but possibly related to my previous posts (Water Ingress), the Mrs hit a large puddle of water on Thursday night in torrential rain, not enough to cause concern just a big splash. Friday morning going to work she noticed the Auto light function warning coming on and then go off again all was well until she was returning from work on Friday night.
    Firstly Auto light function warning came on and went out then head light out warning came on then the car began to chug (much like running out of fuel), so much so she had to pull over, at this point the engine Mgmt. light came on and the car went into low boost, the car drove 6 miles home in low boost with no chugging.
    Today (Saturday) I cleared the codes and the car drives fine but the left head light was full of condensation and was not working(No Warning lights on the dash). On inspection the rear cover of the head light bulb housing was not on correctly so I thought its a bulb, water hit it in the splash and blew it. I dried out the lamp and one bulb later and still no head light, so I tried swapping the bulbs to the right side as it was working, the old bulb and the new one were both working when tried on the right side leaving me to think that the left lamp has a problem.
    Is there an additional Xenon control unit that could be at fault for the lamp at least?
    As always all feedback gratefully appreciated.

    Watery Head Lamp.jpg
     
  2. Duffy3074

    Duffy3074 Senior Member

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    You checked the ballast unit at the rear of the lamp?

    :)
     
  3. M80

    M80 Senior Member

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    20,000 volt be careful how you check it.

    That is if it's HID.
     
  4. Uncle Benz

    Uncle Benz Senior Member

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    Sadly the control module sits on the underside of the lamp, with its electrical connections poking inside through the bottom face. It's the lowest point, where all the water that gets inside the lamp will ultimately collect. I'd wager that when you undo the screws and drop the unit off it will be full of water.
     
  5. Duffy3074

    Duffy3074 Senior Member

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    You can access it by pulling the arch liner back.
    Good bet it's the cause of your problems.
     
  6. star

    star Forum Supporter Authorised Forum Supporter

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    yep lots of water inside that lamp, just changing the ecu may last for a while until more water gets in and your new ecu is also toast.
     
  7. Uncle Benz

    Uncle Benz Senior Member

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    If the open rear bulb cover was the source, you may get away with just the ballast module, but you must make sure the lamp is thoroughly dry. I'd recommend removing it and airing cupboard for a few days with every orifice opened. The lamp! Filthy minded kids!
     
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  8. OP
    PaulOD

    PaulOD Member

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    Yep it's the ballast control unit and a bonus point for knowing it would be full of water, the lamp is dry now so I swapped the driver's side control unit and it worked.
    Will I need to get the OEM replacement control unit coded by the dealer or is it plug and play?
     
  9. Duffy3074

    Duffy3074 Senior Member

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    Plug and play, it’s just a ballast for the bulb
     
  10. Uncle Benz

    Uncle Benz Senior Member

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    I’m afraid not. I think it needs coding
     
  11. star

    star Forum Supporter Authorised Forum Supporter

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    Did you find where the water ingress is coming from?
     
  12. Duffy3074

    Duffy3074 Senior Member

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  13. Uncle Benz

    Uncle Benz Senior Member

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    Last edited: Nov 19, 2020
  14. Duffy3074

    Duffy3074 Senior Member

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    My mistake
    Had picked up on LED for some reason
    If you’ve been in the same position and had to code it, I’ll bow to that experience

    :)
     
  15. OP
    PaulOD

    PaulOD Member

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    The silly prat that owns the car ,aka Me, drove into a flood a while back and both head lamps steamed up, then the same silly prat (me) removed the back lamp covers and left her in direct sun and they dried out lovely, it was my (prat) poor replacement of the left lamp covers that caused the water to get in this time, the passengers side cover was off and slide down behind the lamp, the drivers side was on correctly and has no issues (yet)
     
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  16. Uncle Benz

    Uncle Benz Senior Member

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    It may be worth putting the soaked module in a plastic bag with half a kilo of rice and popping in the airing cupboard for a few days. No guarantee, but I did this with a body control module from my neighbours Zafira recently and it saved a £300 unit.
     
  17. OP
    PaulOD

    PaulOD Member

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    Just tried the control unit after 2 days drying out and no joy, I have ordered an OEM control unit, should be here next week
     

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