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Originally Posted by Spandrel
The floating voltage of 0.040V-0.050V on X12 (pins 6/7/8/9) is anticipated, as those are the Hot/Cold Bulb Filament sense lines from off LKM relays.
As for the Pin to Pin continuities.. I would record the resistance for those less than 10-12 ohms (1 amp current) and see of you can justify those reading by evaluating the circurity.
IMHO,
It is plausible the LKM internal melt down is isolated to the LKM circuit design and specific failure.
1) X12 - pin 20 - Hot at All Time - fused with 200 amp at battery for Body Electrical to include Low Beams.
2) X12 - pin 12 - Hot at All Time - fused with 20 amp for Fog Lights.
I would suggest a printed circuit board (PCB) is doom to complete destruction if anything goes wrong with the circuits on the board with that much current/power potential sourced to the on board circuit traces.
FYI, 12 volts cannot cause or sustain an arc (a condition of voltage induced current jumping the gap between conductors) it can cause plenty of sparking from shorted conductors and heat from low resistance with high current. Ever shorted the battery terminals with a wrench? That will demonstrate my point.
Note: The Fog light relay common contacts are directly connected to X12-12 and is obviously involved in the meltdown and now the question is: how did that happen if the car was parked with the lights off?
Could be, the LKM PCB or a component failed or somehow - the coil for the fog light relay became energized,
..then the battery discharges until the low battery voltage at the LKM causes the fog light relay to Cycle (Off-On-Off-On...battery voltage low with lights on and voltage recovers when lights off) until the relay contacts overheat and/or became a high resistance contact or desolder the relay from the PCB.
I think, I see the PCB component-side pad for the Fog Light Relay is burned away - indicating the heat/sparking from the failed connection.
After that the current at the high resistance relay contact/desoldered relay contact could spark away generating plenty of heat to involve any other nearby material and components that add to the localized meltdown.
Last edited by m6bigdog; 07-15-2022 at 01:15 PM.
meeknet.co.uk
We've seen exactly the same damage on the UK site, exactly the same burn marks in exactly the same place, however we thought it was water damage that started it. I've had a good search and just can't find the thread, I'll keep looking.....
Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i
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Please post what you find! Thanks!
(definitely no water damage here - garage kept and not driven for several days)
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Reference the marked-up Solder-Side LKM PCB attached (originally posted by Revtor).
I don't like to do a bunch of guessing with a circuit failure that has practically destroyed the evidence of the failure mode, however there no other option.
So here it goes and take it for what it is worth!!
As I suspected the Fog Light relay coil is adjacent and in close proximity to the relay common contact (X12 pin 12 - 20 amp - Hot at All Time - Note error pin 20 on my mark-up).
I don't have a LKM to inspect, so I can't confirm if the coil trace next to the Relay common is the coil positive or ground.
If someone can confirm that could be helpful.
If the coil positive is the trace next to the Hot at all Time relay contact?
Note: the Fog Light relay common contact is a small terminal soldered into the PCB (the relay NO contacts are formed by the fame of the relay).
Should the relay common contact become hot (aging contact, higher wattage Fog Bulbs) it could generate a cold solder joint at the PCB and that would add to the heating effect when using the Fog Lights.
A failure of the the PCB being subjected to excessive thermal/heat cycles over the years of Fog Light use could be the culprit that energizes the Fog Light relay coil.
Hence, the fog Light relay could energize with a PCB failure while the car is parked!!
I rarely use the fog lights on my E31 and I anticipate the LKM in my car would be less likely to fail.
Also, this failure would be a caution not to used higher wattage the OE Spec bulbs in the Low Beams and Fog Lights
Has the LKM had similar failures with the Low Beam on-board relay? It may be useful to evaluate the coil and X12 pin 20 (Hot at All Time) arrangement also.
Also, If someone has a failed LKM with Fog Light problems I would be of valuable to evaluate a failure; that didn't completely destroy the Fog Light circuit and relay
Last edited by m6bigdog; 07-16-2022 at 01:14 PM. Reason: clarity
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FYI - Fog Lights On!!!
Spandrel - You would not be the first...
https://www.bimmerforums.com/forum/s...hts-staying-ON - Reply #7 - I have the same problem, except mine are flashing slowly.
email reply from OP: I got nowhere with this fog lights staying ON issue on my E31 and rather than paying over one thousand dollars to replace the LKM
I decided to just pull the fuse for the fog lights that also controls the horn . So I've been driving for the last eight years without the
fog lights. Oh well . . .Willy G.
https://www.bimmerfest.com/threads/1...issue.1293481/
Also: Willy G
https://www.bimmerforums.com/forum/s...ics-1996-840Ci
Last edited by m6bigdog; 07-17-2022 at 01:39 PM. Reason: add to update reply
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That sure sounds like the failure scenario described. When I saw the car smoking in the garage, the lights were popped up and the light was dimmer than full headlights. This could be due to only being fog lights on, or that the battery was low or both - I didn't really get the details at the time as I was trying to push the car out of the garage to prevent it from burning down the house if the fire got larger, and getting the trunk open to disconnect the batteries. This does make me feel better, as I've not seen anything that really jumped out at me about the condition of the wiring harnesses - a PC board and relay failure seems to make sense and seems to have happened before. I do generally run with fog lights on too, as I'm at this point used to much brighter headlights in more recent cars, so that makes sense from a thermal cycling standpoint.
That said, of course, I need to find a replacement board (sounds like some here may be able to help me out), and get it coded (I'm hoping my local specialty shop can handle the coding, but if the dealer is the only option then they are...). I did try to fire the car up when I had the batteries installed, and while the starter will turn over just fine, the motor wouldn't catch at all. Before I go diving into the Air-Fuel-Spark triangle, is there something in the LKM that would restrict starting (I think I read somewhere that a copy of the odometer reading, among other things, is stored in the LKM to prevent manipulation, and thought perhaps there's some other security something in place)? The car had no starting or driving issues previous to the LKM failure...but trying to start without the LKM in place sure generated the Christmas Tree failure mode of lights and messages on the MID...
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Once the LKM meltdown is under way, all kinds of unpredictable lighting problems will occur as the LKM circuit failures migrate from the heat.
Securing a used LKM might not be as good a solution as it sounds - as usage of the fog lights may be the major contributing factor for the failure you experienced!!
That I'm aware the LKM is only that, however the Instrument Cluster and EKM (Body Electronics Module) share data for odometer mileage security.
The engine start problem may be the alarm disable function. I would investigate the vehicle Anti-Theft Protection and Drive Away Protection features.
I’m seriously considering pulling the F9-20 amp fuse for the Fog Lights on my 8, just because the potential for failure is too high and the cost of a meltdown and vehicle damage would be horrific.
The only solution I could conceive that would eliminate the LKM failure mode would be to:
remove the internal fog light relay and mount a more robust relay off the LKM circuit board (i.e., harness wires from relay contact terminals on the LKM circuit board to a relay base through the LKM case). This would remove the F9-20 amp - Hot at all times and the relay coil power from the LKM PCB and the LKM would work without light check errors.
Thanks,
Not to be an alarmist, however:
I would suggest writing a letter to BMWNA, contacting your insurance company to file a claim and/or filing a unsafe vehicle report with the NHTSA.
After all, this vehicle electrical failure had the potential to burn down your house and kill the occupants!!
A manufacture recall and repair support would be a good thing for the remaining E31's on the road!! even if it takes years!!
Last edited by m6bigdog; 07-17-2022 at 03:25 PM.
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I think I will definitely stop using the fog lights regularly - remember, though, if you pull Fuse 9, you also lose the horn which is also a safety feature, as well as having some impact on the windshield washer pumps... Truthfully, I think that we, as a community, should start looking into creating replacements for all the electronic modules in the car. BMW obviously is not going to replace them, and they will eventually fail in all the cars, possibly resulting in fires. Otherwise the only future options will be to drop in a LS or something that has lots of modern aftermarket support, and I don't think anyone really wants to do that.
I'm definitely mulling an NHTSA report, although with the low volume of cars on the road (numbers probably in the hundreds world wide at this point), I'm not sure they'll care.
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I did pull F9. I think, not burning the car and/or my home down trumps disabling the horns safety feature.
I will start on an upgrade design for the LKM off board Fog Light relay and I may also include the Low Beam relay. Once I implement the upgrade I'll reinstall F9.
While there are many cars that burn down due to many reasons to include lack of maintenance!! The electrical systems should not be the primary starter of the meltdown event. That is what fusing is all about!!
The US E31 just has Fog Lights and Horns on F9. The Windshield Wiper Pressure control is most likely a European option.
The windshield washer fluid pumps and nozzle heaters are supplied by other fuses.
As far as the life expectancy of the E31's electronics modules?
I should anticipate 30 years is beyond the life expectancy that vehicle manufacture would design for.
I anticipate you are correct, most of the electrical/electronic body system control modules will fail before 30 years.
However, they will for the foreseeable future be repaired with easily available parts.
Power supply filter capacitors will be the majority share of these failures. #2 will be switches and transistors also available by substitution.
The body wiring harness and modules that melt down will be the failures that push a vehicle into salvage status.
Not that the car can't be repaired. It will be the hours invested to rebuild. Hence, if the E31 isn't a high value example (low mileage and/or pristine) or repaired by a passionate owner it will be parted-out.
NHTSA's main function is to reduce transportation related damage, injury and deaths.
While they certainly have bigger issues on their plate, the actual damage and occurrence numbers for the LKM meltdowns on the E31 (inuse/attended/unattended) as well as the damage to structures where parked will not be known until someone or some agency tracts the occurrence.
Insurance companies also do a lot of event tracking for the claims they payout and if no one files a claim or the primary cause is not determined it didn't happen.
Most safety codes and recalls are insurance industry driven!!
I know of 4 LKM Fog Light failures including your 840!! That is a lot. Given, vehicle age and Fog light usage seems to be the primary factors with each occurrence, I anticipate it only will occur more often if the design flaw is not corrected..
Last edited by m6bigdog; 07-18-2022 at 04:59 PM.
meeknet.co.uk
Similar module burning: https://www.bimmerforums.com/forum/s...ics-1996-840Ci
I'll keep looking for the one that was identical
Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i
My BMW Repair YouTube Channel
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I see the Body Electrics Module picture, but the photo bucket links are dead it seems. Sounds like the same issue, though. I think this link is in @m6bigdog 's post as well, unless they are updating it to add what's found in other replies
Last edited by Spandrel; 07-19-2022 at 07:31 PM.
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Tim,
Thanks for staying on this.
Your site is the go to for the E31 - I anticipate this issue will salvage more & more E31's as they age!!
Would be nice to get a look at and test a LKM that has failed with the Fog Lights On but yet to meltdown, just to analyze the failure mechanism, i.e., burned PCB, solder joint, relay contacts sticking, etc...
I anticipate most of these "Fog Lights Stay On" failures do not end up in a meltdown, but that is just luck as the potential is obviously there to completely burn down a car!
When the LKM fails without the Fog Light relay causing a meltdown, as occurred to wgeorgio/WillyG in his Posts, they know something is wrong because the Fog Lights will not turn off and they can take immediate corrective action - like removing F9 as the emergency no drama solution.
However, as seen:
Beagle2 Post, the LKM total meltdown occurred while the car was being driven. Unsure if the Fog Lights were On? Where there any early indications days before? Doesn't really matter as the meltdown did happen and the damage to the 3 modules speaks for itself!
Spandrel's LKM meltdown, occurred while his 8 was unattended, parked in the garage - in the middle of the night. He does claim to use the Fog Lights often with the head lights.
I anticipate regular Fog Light usage is the major contributing factor and after many years; the Fog Light relay and/or PCB fail in such a way - Poof!!
No easy solution, even if the LKM wasn't NLA as a new LKM would just reset the time mark to a possible future LKM failure.
I anticipate replacing the internal relay with an external Fog Light Relay and keeping the Hot at all Times power out of the LKM is the only viable option to keep the Fog Lights functional and reduce the meltdown occurrence.
In the 18 years of E31 ownership, I rarely use the Fog Lights, so I anticipate the LKM Fog Light relay/PCB is in good condition, however I still pulled F9 as a precautionary measure; as IMHO, the LKM meltdown is both unpredictable and devastating.
Last edited by m6bigdog; 07-20-2022 at 03:55 AM.
meeknet.co.uk
Very kind of you Rod, thanks!
Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i
My BMW Repair YouTube Channel
My Current 840ci Sport Individual
My Current 650ci Sport Individual
My E31 Repair and Information Website
My E38 Repair and Information Website
My E63/E64 Repair and Information Website
Chase - Heroes to a generation
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Soooo now that we seem to have settled on a cause, @cartoonz , @m6bigdog ... @AnyoneElse ... Anyone have a spare LKM I can pry loose from you?
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If anyone has one it will be Wuffer.
Go to:
https://www.wuffer.ca/
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No reply after a week to the 'Contact us' page on wuffer.ca. Is this usual? I don't want to spam with requests, but I don't know what their normal response time is, either...
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Bummer,
I got a hold of Wuffer last week.
He has moved and retired from the E31 Parts Emporium business.
He said his son will take over, but unsure when.
I'll check another individual that has dismantled a number of E31's.
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BMW CCA Member
Hey Gents-- Sorry I'm late to the party, this thread would have been right up my alley for a deep dive. Spandrel, sorry for that fire! hope you (or we) can get to the bottom of it! I've scanned the thread pretty quickly, but it's certainly important we get to the bottom of it! I'll re-read it in the next few days with a little more detail.
I will say that for a few years, my E32 has had an issue where it continues running after turning the key off and removing the key, IFF the parking lights are still on. Turn off the headlight switch and car shuts off. Everything else seems to work OK; Bizarre. I chalked it up to a shorted wire somewhere in the harness between the parking light circuit and the hot-in-run circuit; I'm fairly sure I don't have any aftermarket stuff in there that has those two circuits in one place. Anyway, It's been parked about 5-6 years without a battery, so I'm not terribly worried about it, but the two points I want to make are:
1) Studying the E31 diagrams trying to come up with an answer is great, but when the hypothesis can include is something "hot at all times" shorted to something that's "not", all bets are off if the problem is two unrelated circuits fused together by a vermin bite/broken down insulation, etc.; particularly if the destination of that hot-at-all-times energy is something that can't take that kind of power (Like 12V across a 2.4ohm resistor)
Some quick math... V=IR; I=V/R so 12V/2.4ohm --> 5A ; That said, that's 60W, way more than enough to start a fire in the wrong place.
Similarly, tracking down the co-location of two hypothetically shorted circuits would be a bit of a challenge.
2) SOOOO MANY modules in our cars have dual or even triple power supplies; failure of any number of diodes/silicon IC parts, sticky relays, etc., can and would lead to one circuit back-feeding another. Even just powering a module by 2 of the 3 fuses needed could lead to quirky results and voltages across parts that wouldn't normally be observed, plus the added insult of extra current coming from the 'wrong' fuse.
In the case of my E32 continuing to run after the key is turned off and removed (so long as parking lights are on), surely the parking light circuit is carrying some extra weight to keep whatever relays/circuits energized that are keeping the car running. This would be a concern of mine, if, for instance, powering some of those circuits was being done via a surface mount shunt resistor like the 2.4ohm in the LKM.
I'll get back to y'all in a few days! Also of note, I probably do have a spare E31 LKM around, I'll check my pile.
'89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!
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Please do check your pile! I'm down to considering parting it out at this point. I had my B7 sit immobile in the driveway for 10 months while I sourced a custom machined impeller wheel for the supercharger... I'm not really up for that experience again.
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Hi, are you still repairing body control modules? I need mine repaired, let me know please your price to fix and directions for sending to you.
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BMW CCA Member
yes-- I am-- send me a DM with your email address and I'll send out my usual offer/removal instructions/shipping info!
'89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!
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Any updates on your pile? Next step is parting out.
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BMW CCA Member
Sadly, no, I didn't have a spare LKM. Only ones from 5/7 series
'89 735i, '91 850i, '81 MB 380SLC (For Sale), Tesla Model 3, and VW Passat TDI -- Yes, I still repair General Modules, DM for info!
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There have been several sold on eBay $300 during the last several weeks.
I was thinking you would look there?
Another one should show up soon...
https://www.ebay.com/itm/13419085662....c100667.m2042
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hi, since I am a new member, I don't have private messaging enabled yet from what I have read previously, I would have to post at least 10 times and wait 7 days, are you able to dm me ? I already have the bcm out.
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