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Light Control Module or Other Problem?

Discussion in 'E39 (1997-2003)' started by AngryE39, Sep 26, 2009.

    • Member

    AngryE39

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    Vehicle: '01 E39 540iA with 103k miles.

    Symptoms: While driving my car about 6 weeks ago, I noticed that my turn signals were not "blinking" on the dashboard, but the turn signals were on (and not blinking) on the exterior of my car. The turn signals all started working again after a few miles.
    This past week, the alternator died. My indie BMW shop replaced the alternator with a remanufactured Bosch unit, replaced the related pulleys, tensionors, etc and the car ran fine. The next day, my turn signals (and emergency flashers) stopped working during a 2 mile trip to lunch. This time, though, I had no turn signals (on the dash or outside) nor emergency flashers. But, I swear I think the pixels in the instrument cluster were "pulsing" (glowing brighter, then slightly dimmer) at the same cadence as the blinkers would normally flash!?! Then the lights all started working again (and the dash pixels stopped "pulsing") a half mile later, before I turned off the car. So on my way back from lunch I stopped by my mechanic's shop. When I described the symptoms with the strange turn signal/emergency flasher incident, he thought it could be the Light Control Module (LCM) and he briefly speculated that a bad LCM "could have taken out" the alternator. He plugged into the car's diagnostic system and ran a check for error codes and found none. He visually checked the battery and a few items under the hood, found no problems, pronounced the car ok and said I should just keep an eye on it, and sent me on my way.

    Question #1: Does the chain of events I have described (intermittent flasher problems and dead alternator) sound indicative of a bad LCM?

    Question #2: If it is the LCM, can I replace it myself and does some code in the car's computer system need to be re-set by a BMW dealer at the time the LCM is replaced? (I read something on another on-line DIY link that said a dealer had to "validate" or "initialize" a new LCM to the car or the car's computer would have some type of permanent error code, like a new odometer!?!)

    Question #3: If it is not the LCM, what other items should I check?

    I would appreciate any feedback. Having owned a few British cars years ago, I am a little sensitive to intermittent problems with automobile electrical systems.

    Thank you.

    vtx guest

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    Seen something similar on my friend's E46 a few months ago.

    The root cause turned out to be shorting out of the fuel pump power circuit to fuel sender circuit. Plastic around fuel pump power pins on the fuel pump/sender connector was melted.

    Also was fried the part of the instrument cluster PCB where the wires from the fuel sender were coming in (unfortunately, he forgot to take a picture). Some traces were just hanging in the air, some came unsoldered. Being hardware engineer, he promptly soldered everything - and got away without replacing the instrument cluster.

    All this sounds far fetched, but I'd check the fuel pump/sender connector, just in case - this is E39, not E46, so no telling what circuits would be affected. In his case, those were fuel senders, high beam, fog light and turn indicators.

    If you get to the instrument cluster and find parts of it fried, it may still be salvageable - but better check back, for there are some non-trivial tricks that yu need to be aware of.

    Good luck.
    • Member

    AngryE39

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    Thank you for the sggestions. I'll keep an eye on both the fuel pumkp unit and the instrument cluster.
    • Member

    102929

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    It is most likely the LCM - but it could also be a communication issue on the buss between the LCM and some other modules. If you diagnosis actually looked at fault codes for all modules, including the buss network then it is strange there are no codes.

    A replacement LCM does have to be coded to your specific car and must also be of the correct version.
    • Member

    az3579

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    Most probably LKM. Chris just had the same problem, and his car has been out of commission for over two months trying to diagnose the problem. He has tried swapping the cluster (twice), but he just bought a used LKM (nicely enough the same exact year and model!) and everything is working great!

    (I don't know why they were calling it LKM instead of LCM though... :confused:)

    Autohaus guest

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    A used LKM/LCM will work but it has to be the same model and part number. Also it has to have the same hardware/software numbers to make it work. However, some problems may still come up. For instance, I don't have DRL's anymore. I really never cared for them in the first place. Second, by installing a used light control module, a red tamper dot shows up next to the odometer. AZ knows my frustrations over the past couple of months but finally everything (except for no more DRL's and a red tamper dot) is working...knock on wood.
    • Member

    az3579

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    And occasionally your right-side angel eyes don't work, and the turn signal stays lit up when not in use (but still blinks when turned on).
    • Member

    AngryE39

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    Thank you all for your suggestions. I'll keep an eye on things and provide an update once I have to deal with this issue. (I have to admit, reading some of these replies, I am starting to have flashbacks to my MG Midget and its Lucas electronics.)

    Autohaus guest

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    Well AZ, since that night it hasn't been doing that so maybe I had a temp glitch of some sort. Angry, keep us updated.

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