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Tech Question: E46 LED Turn Signal Malfunction?

Discussion in 'E46 (1999-2006)' started by mgroenig, Sep 5, 2014.

    • Member

    mgroenig

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    Hi all,

    First time poster here at the CCA boards, but hoping for the answer I can't find elsewhere.
    I've searched this forum, M3 forums, e46 fanatics, and the web in general... no luck so far.

    I have a 2004 M3 w/ the LED tails, very low mileage garage queen.
    The car sat for a year in my garage with a dead battery.
    I recently resurrected it and we moved to a new state.
    The car had no issues (other than not charging the battery, which an alternator replacement took care of) when it was parked.

    Now, the passenger side turn signal flashes fast and the dash has an idiot light lit for the rear passenger bulb. Checking outside the car, I can see that the brake light is flashing in place of the turn signal (and at a rapid pace).
    No LEDs on the turn signal are illuminating.

    I checked the LED tail unit and it looks like no maintenance/service is intended on it.
    I checked the connection and I don't see anything obviously wrong or troubling. The contacts look clean and the wires seem normal.

    Because I don't have just a few LEDS non-functional, I think it's something OTHER than the traditional 'I have a few LEDS out... must buy new light' issue.

    Does anyone have an idea what my issue is? or how to best troubleshoot it?

    Thanks in advance,

    Marcus
    • Member

    MGarrison

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    Not sure what to suggest about the lights, but perhaps have your battery and charging system tested - not sure if E46's are as sensitive to proper electrical power supply as later bimmers, but general unexplained wonkiness sometimes is a weak battery. With your battery having sat dead for a year, perhaps it didn't retain or return to it's full charging/discharge capabilities.
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    • Technical Service Advisor

    charlson89

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    I can't remember off the top of my head if you could take the left tail light and plug it in on the right side and see if it the turn signal works then. Let us know what you find.
    • Member

    mgroenig

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    Good Advice.
    I'll try to do that tonight, or at least one night this week.
    I was afraid the connectors might be different (or at least wired differently) left to right... but there's certainly one way to find out.

    besides.... this gives me an excuse to clean behind both tail lights ;)

    I guess what I was hoping was that there was some sort of control/command module that told the lights what to do.. and maybe I could trace back to it and find something odd about it or the wiring.
    Perhaps testing swapping the lights both ways will help give some initial clues.

    Thanks,

    Marcus
    • Member

    mgroenig

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    Yeah... guess I wasn't specific enough in my message.
    I broke down and had the local BMW dealership test the car's charging system.
    They IDed the alternator and I had them replace it before the car was shipped to our new home.
    I also bought a brand new battery.
    I don't think the issue is related to weak battery or charging system now (but we'll see).

    You are right though... when the battery was weak, strange things would happen in the car.
    My car is SMG, and the transmission does very strange things (like refuse to shift, shift on it's own, flash and refuse to do anything, etc.) when the battery is weak.

    Thanks,

    Marcus
    • Member

    mgroenig

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    Ok, post-weekend update:

    Swapped the passenger (trouble) light over to the driver's side of trunk and hooked it up to the driver's side wire.
    Same response (as when it's in the normal location): rapid flash of brake light, no flash of turn signal bulbs.

    I'd assume that places the issue within the light.
    Looking in the rear of the housing, I see exposed circuit boards...
    seems reasonable that something might have crawled (or splashed in there, trunk was open for 6+ months while in garage as I tried to test charging/discharging in the car) in there (small bug) and died, perhaps creating a short.
    If I'm lucky and it's something like that, should be a pretty easy issue to spot and fix.

    The rear housing of the light is held in place by several torx screws.
    Once they are removed, I still cannot get the housing to separate/open.

    Any ideas on how to get the tail light open?
    I don't want to damage it, as I'm hoping to repair it and save the $$ of buying a new one.

    Thanks for the ideas and support again,

    Marcus
    • Member
    • Technical Service Advisor

    charlson89

    Post Count: 2,232
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    Marcus,

    Those tail lights are sealed and are not meant to come open. But you can use a heat gun and a exacto knife to cut around the sealed area to get to the LED board. It's very common for these taillights to fail sadly. Good luck

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