Very interesting stuff. May be close to answering one of the questions I still have about the lighting.

I summarized this in a different thread on turn signal bulbs (5W/21W) where the weird thing is that the bulb spec is two filaments, but the wiring sends only two wires to the bulb (I confirmed this since my original post there).
https://xoutpost.com/1116362-post12.html

And again on that situation I had, the bulb was apparently not burned out - both filaments were intact and showing finite resistance. Yet the LCM was flashing other lights until I swapped the bulb for a new one. So it seems the LCM is smart enough to tell when resistance gets out of spec or some other way to detect impending failure. Wow. It's the sort of thing that makes me want to just to what it wants, vs. trying to outsmart it with a wiring mod.

Any confirmation on how the LCM could flag a bulb as bad when it has not yet burned out? And it was right. Swapping in a new bulb fixed things. Swapping the "bad" bulb back in, as a test, caused flashing problems again.

Why do they specify dual filament bulbs when they only send two conductors? Are both filaments used in parallel? Only one? Why not just spec a single filament bulb?

Well, all I can say is that we've come a looooooooooooong way since my 1960's GMs with a wire, a socket, and a bulb. Good bulb = light. Bad bulb = no light. Now, you need a doctorate degree to change a bulb...

The system measures the current draw. If out of spec high or low will indicate failure. LED lights take far less current and will indicate a failure when functional for example


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Dual filament bulbs are used due to the capability of the LCM III & IV to manipulate output levels and replace lights when a bulb (or filament in a dual filament bulb) fails. Turning lights and brake lights uses the higher watt filament in a dual bulb...were as regular running (tail light) lamps use the lower watt filament. If BMW uses a dual filament bulb in either locations...then the replacement light & output voltage feature can easily be used to illuminate the bulb for whatever "emergency" purpose it may need.



The driver gets the warning (and 80% just look at the lens from outside the car and think nothing is wrong)...but if you actually take the time to pull the bulb/bulb holder to check visually, you will usually see that a filament is burnt or failed/fallen apart. :)

I think the question was why does BMW spec a two filament lamp when only one filament ever gets power. The only thing I could think was that only one lamp model is required for all four tail lights and bonus: you could swap run and brake light when a filament blows.

I have 01 and no power to the brake filament on the top lamps until I put in a jumper to do something about that. Fortunately by doubling the power to the brake circuit I didn't get some error. Just badass bright brakes.


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Yeah - crazy right...?

Here's another variation - green and black. WTH...?

https://ms9hdq.blu.livefilestore.com...mb[35].jpg

Seems like the pre-facelift has some variation in the lamp holder configuration. The rear lower lamp holder can be found in green, white or black.

At this point the only thing I'm sure of is that facelift (LCI) cars should have all white (2-pin) lamps and holders - top and bottom. Pre-facelift cars seem to vary a little but seem to have green in the upper position (dual filament lamps, three contact holder) and possibly just a single filament lamp in the lower position (two contacts).

The wiring diagrams show three different wiring/lamps configurations for the pre-facelift e53 tail lights but only one for the facelift (LCI)....

Up until 2001/08 - https://www.newtis.info/tisv2/a/en/e...0i-sav/b12ZRPJ

2001/09 - 2002/02 - https://www.newtis.info/tisv2/a/en/e...0i-sav/bb6V8Ee

2002/03 - 2003/08 - https://www.newtis.info/tisv2/a/en/e...0i-sav/nh5yjn1

2003/09 and up - https://www.newtis.info/tisv2/a/en/e...0i-sav/skUQRnP

Woof... :confused:

If you get varying levels of brightness side to side, check the tabs on those sockets and the contact area on the housing. Mine were pretty wrecked so I fixed with some solder to build them back up. I also experienced a dim left side that was the result of corrosion in one of the electrical connector pins that plug into the housing from the harness. Some tips that might help.

First off, sorry that I'm confusing a thread on brake / tail lights with my specific questions regarding the turn signal lights, but similar issue with dual filaments.

So on the question of why use a dual filament if they only have two wires going there. Keeping it simple here, because I'm still not clear:

Do both filaments get used? I.e., do electrons ever flow through the fat filament and the thin filament?

So for the two wires that go to the bulb, how are they connected. E.g., one wire is 12V PWM controlled by the LCM, the two filaments are wired in parallel within the bulb socket, and the other wire goes to ground or back to the LCM. I don't know if any of that is true - so please correct or confirm.

If that is the way it is, then again, why use a dual filament bulb if they're not using the filaments independently. And unless there is some really smart and small circuitry embedded in the bulb socket (I think not), the two filaments are not independent. :dunno: But I don't want to underestimate the LCM engineering here, so tell me what I'm missing so far.

Found the post where I detailed the repair of the rear lamp assembly.

What's broken on your E53 today!
https://r.tapatalk.com/shareLink?sha...3&share_type=t

Firstly, only LCI cars (after 2003/09) have any PWM control over the lamps - earlier cars just use lamps that are either on or off, controlled by the LKM.

Secondly, I've not seen a dual filament lamp in a single socket - but that doesn't mean that BMW doesn't do it....

For a dual filament lamp to be of any use in a standby capacity the second filament MUST be wired to the LKM. Your comments indicate that the socket is not wired for a second filament (and the circuit diagrams back this up), meaning two wires to the lamp, not three.

The only conclusion I can draw is that a PO has installed an incorrect lamp. Or lamps... :dunno:

When the LKM uses an alternative lamp to substitute for a failed lamp, it actually turns on a different circuit. For example, in a pre-facelift car, if a tail lamp fails, the LKM will apply (reduced) power to the brake lamp, as a substitute for the failed tail lamp.

In an LCI (facelift) car the brake lamp is normally only the lower of the two rear red lamps. If the lower (brake) lamp fails, I think the LKM will then use the upper lamps as a brake lamp (as well as the tail lamp function) until the lower lamp is replaced. This upper lamp is also used as a brake lamp during the "force dependant" braking mode - i.e. when you hit the brakes hard!

Looking at the circuit diagrams, the only locations I can see a dual filament lamps (12v 5/21w) on the e53 is the lower and middle rear positions, acting as a tail/brake lamp - but only on cars from 2001/08, when "force dependant" brake lamps were introduced. And from 2003/09 they dropped the dual filament lamps in favour of single filament lamps and PWM.