Bulb Failure....but no bulb failed ?

Discussion in 'Electronics' started by GregE240, Dec 31, 2002.

  1. GregE240

    GregE240 Hardcore MB Enthusiast

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    Hi,

    I've got a slight problem on my 1998 E240 Avantgarde. When I have the headlights on and switch on main beam, after a second or so the "LAMP DEFECTIVE" sign appears in the little screen in the speedometer. Looking at the front lights last night, it appears that both main beam units are working correctly, and the blue light appears on the instrument cluster when the main beam is activated.

    The only thing that I can think of is that both main light units should also light up on main beam, but currently are not. If this is the case, then both bulbs (or a fuse/both fuses) are blown. If it is fuses, are they under the bonnet, or in the side of the instrument cluster, or near the battery ?

    Ideas anyone ? Its not due a service for about 3 months or so, and I don't want to take it in when it would appear that both main beam units are working okay.

    Many thanks in advance,

    Greg(E240)
     
  2. Brian WH

    Brian WH MB Club Veteran

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    Sounds as if you have an electrical short on the headlight wiring or the bulb holders.
    Not the fuse I don't think.:devil:
     
  3. Koolvin

    Koolvin Administrator Staff Member

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    I believe tha lamp defective could also mean the rear lights as well! including the brake lights and indicators, have you checked the operation of all the lamps FR and back?
     
  4. Simon

    Simon Hardcore MB Enthusiast

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    Don't forget your number plate lights.
     
  5. paulrstaylor

    paulrstaylor Hardcore MB Enthusiast

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    And some functions have more than one bulb in the same cluster, like the rear sidelights on my W202.
     
  6. OP
    OP
    GregE240

    GregE240 Hardcore MB Enthusiast

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    Thanks for the replies, folks.

    You're right about the bulb failure module in as much as it covers other bulbs on the car, but it only lights up when I select main beam, no other times.

    For example, I has a reversing light fail just after I got the car, and the LAMP DEFECTIVE would only light up when you selected reverse.

    Looks like one for the dealer at the next service. It can wait !
     
  7. Koolvin

    Koolvin Administrator Staff Member

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    Have check to see if the main bulbs are the same (reccomended) Wattage?
     
  8. Mark300SL

    Mark300SL 1962-2010. Gone, but not forgotten.

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    A burnt contact or bad earth on one of the bulbs would do this

    IIRC the system measures increased resistance - We had it recently on the SL - it was just a bad bulb connection - the tail light worked but it wasnt as bright as the other one - new bulb cured it!

    Mark
     
  9. Koolvin

    Koolvin Administrator Staff Member

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    Do you have Xenon ?
     
  10. OP
    OP
    GregE240

    GregE240 Hardcore MB Enthusiast

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    Koolvin: Don't have Xenon, I'm afraid. I don't know if they're the same wattage.

    Now I've confirmed that they take H7 bulbs, I'm probably going to upgrade them with Philips Vision Plus at some stage.

    Mark: Could be. It could be early warning of imminent failure I suppose. I just don't use main beam that much, to be honest. I'll see what happens when the new bulbs go in. I assume the earth for them is pretty near the light units ?

    Thanks both.

    Koolvin, I'd just like to say the "Turbo" thread has made excellent reading. Congrats on your installation - it looks superb, even though you (modestly) say the engine bay is in a bit of a state - it looked fine from the photos !
     
  11. OP
    OP
    GregE240

    GregE240 Hardcore MB Enthusiast

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    Ok, an update:

    Did as threatened and bought Philips Vision Plus bulbs. Worth a punt, definitely better than the Osram bulbs that were in there.

    But...the problem is still there !! :mad:

    So, I'm thinking it might be the failure unit itself....any ideas how much I'm gonna get stung for one of them ?

    Not pleased !

    PS - The LAMP DEFECTIVE only comes on when the engine's running. All other ignition positions you can put main beam on and it's fine.
     
  12. Shude

    Shude MB Club Veteran

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    I think someone has a nice excuse for an HID upgrade... :rolleyes:
     
  13. OP
    OP
    GregE240

    GregE240 Hardcore MB Enthusiast

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    How much then, Shude ? Any changes in wiring needed ? I've got headlamp wash already. Its a 1998 model.

    Cheers,

    Greg
     
  14. OP
    OP
    GregE240

    GregE240 Hardcore MB Enthusiast

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    OK, final update:

    After replacing both headlight bulbs, and still getting the problem on main beam, I said I would wait until the next service.

    Until a sidelight blew this week!

    Seeing as these share the same lamp unit as main beam I think some of you are right in saying it monitors the resistance - presumably both main and side share a common earth point which may have led to the reading.

    So, armed with experience I went to get the bulb out on Wednesday afternoon but couldn't budge the bulb holder. Phoned my local dealer who informed me that they twist out, but did sir realise its a special bulb that only M-B supply? Well, no actually.

    Booked it in to Gerard Mann (Birmingham) this am, took the technician 10 mins to fix. Waited, chatting to the service guy about future work, how they will almost certainly be where the car goes for its next service. And he promptly tears up the bill. No charge sir, we'll see you at the next service.

    Faith in humanity restored.
     
  15. fuzzer

    fuzzer MB Club Veteran

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    I must be dreaming , i thought that technician gave you something for nothing ...

    Need to get my eyes tested:D
     
  16. OP
    OP
    GregE240

    GregE240 Hardcore MB Enthusiast

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    **SORTED!!!**

    Well, I fixed it last night.

    After a recent post (either here or "the other place"), I thought it was either the contact with the main beam bulbs themselves, or poor earthing.

    The latter was discounted quite quickly as it would appear that the headlight units on 210s have a huge multiplug that slots in, dishing out wiring to all bulbs plus the headlight wash. Given this earth seems to be shared by everything in the cluster, I didn't think it could be that.

    So I started with the offside (you lose less skin getting to this one, I remembered) I took the plug off the main beam bulb and gave it a good sanding down in the contacts and a good dose of WD40. Recrimped the contacts and whaddya know? Sorted!

    That deserves a banana methinks :bannana:

    So I'm well chuffed - main beam now works a treat and no bloody annoying nagware in the dash telling me a bulb's gone south when it hasn't!
     

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