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I would like to know what are the statistics of BCM fires that occurred with Trickle Charges or without. Anecdotal reports do not tell the real picture. Thanks Gene
MB superseded the part number for the BCM and the latest is backwards-compatible with all R230s.
What is the part # for the supercede BCM?
Do you know the part #'s for the wire harnesses that plug into toe BCM?
There aren’t any wiring harnesses that plug just into the bcm. They are part of the 35’ main harness that runs through the car. Yiu will have to find a used harness or cut one to splice.
For the guy who started the thread about upgrading his audio, this is why I stuck with stock. In that same thread I mentioned numerous electrical issues after upgrading the radio in a previous SL. Never touched it again
"Nothing that touches the electrical system is modified from stock. No aftermarket multimedia units, not even tapping the fuse box to hardwire a radar & dashcam"
All the non-battery cables should be fuse protected so it's probably the battery cables causing the short, probably caused by shorted power transistors. It would be handy to have a schematic of that module but I bet that's not available.
Hey Gene, look at the video at about 1.06 minutes in you will see a box and a charger made by Schumacher. Don't know if it was hooked up at time of fire, but.....
Oh Boy !?! I have to say there are so many electronic engineers as owners, We need them to get together and figure out what is going on and create the safety disconnect to prevent this damage. Do we trickle charge or not? Do we replace them every few years? What component goes on fire first when their is no apparent or minimal current draw by the normal operating of the car when at rest? There is no doubt the fire needed quite a current to start. How does that current in the BCM go ground to start the fire ?. I have read here some attempts at some analysis. But the goal if reached could be a simple auto shutoff add on. This can be solved. Gene
Getting a circuit diagram of the unit is the key to solving this, but I can't see how we'd get hold of it.
A forensic fire investigator could determine precisely where the fires start. We could do an MB World pass the hat around and crowd-fund it. Someone with a burnt-out car would have to be the guinea pig.
Well here you go, further proof that it’s real , not isolated,and dangerous. This is a working bcm pulled from my sl55, 45,000 miles. This is the newer version as well not the old version.
Getting closer to pinpointing the cause. Thanks for pics.
I'll pull mine sometime and strip it to identify those SMDs and see if I can figure out where they would be in the circuit. That 4453 chip in line with the burnt SMDs is a Shottky diode which shouldn't be passing that much current. It might be possible to put a fuse in line there and monitor it. I wonder if your BCM is actually performing correctly, with those burnt SMDs? I'd like to get the circuit.
Car is technically totaled, but being an SL55, I would probably fix it if it were me.
Update to this post, I am the new owner of this Sl55. It only has 30k miles and is in excellent condition. About to find out exactly how much work it is to repair this damage. Car is just too nice to go to the boneyard. I'm not always great about taking pictures and documenting everything, but I will try on this project.
Mike, if the shorted BCM produces such a current draw to heat up the cables and melt the insulation, wouldn't be a solution to put a 250 amps fuse in line with the battery cable which should burnt first before all that catastrophic damage occur?? I don't think that any of the accessories will pull more than 100 amps at a time. The most load should be the Vario roof hydraulic motor!
Mike, if the shorted BCM produces such a current draw to heat up the cables and melt the insulation, wouldn't be a solution to put a 250 amps fuse in line with the battery cable which should burnt first before all that catastrophic damage occur?? I don't think that any of the accessories will pull more than 100 amps at a time. The most load should be the Vario roof hydraulic motor!
There are no wires near the bcm that will handle 250 amps. The wire is now the fuse, thus the fire
Trying to take a fresh look at this BCM issue. I'm not an electrical engineer, but I do see that there are a number of filtering capacitors. I have also seen several modules, one on this thread, that show definite signs of these caps failing by shorting. That's not unusual, especially with ceramic caps. So, can anyone explain why this was built with full battery amperage available to it? No overload/short protection externally and none internally that I can see. Why? The one module other than the ECU that has some pretty heavy power electronics and absolutely no protection?
I'm not a lawyer, but how do you defend that in court if you are Mercedes? Did you know that capacitors fail by short circuit? (Yes), Did you know that in a filtering application across a large difference in potential, that such shorts are a potential fire hazard? (Yes). What did you do to limit these short circuit currents? (Nothing). Tell me where I'm wrong.
I'm wondering why there is no provision for a fuse to protect this controller as well. Perhaps there is a way to add a fuse to the high amperage input to protect the board?
If you read the other thread on this subject a fuse is discussed but there would be a fire anyway in the wiring harness which contains 12-16 gauge small wires. They are the fuse and they burn up. In other words the fire is in the harness and bcm not before it. So a fuse is useless. Think of it this way the fire starts before a 250 amp battery fuse would blow.
Getting a circuit diagram of the unit is the key to solving this, but I can't see how we'd get hold of it.
A forensic fire investigator could determine precisely where the fires start. We could do an MB World pass the hat around and crowd-fund it. Someone with a burnt-out car would have to be the guinea pig.
My hobby is electronic repairs of high end test equipment.
I regularly reverse engineer such boards, in order to produce schematics so I can fault find on them.
I take several high resolution photographs of both sides (if it is not a multilayer board) and then painstakingly draw them out.
I have been looking for a BCM for about 1 year, so I can reverse engineer it.
However here is the problem, no one wants to give away their old BCU. I saw a burnt out BCU on eBay for £300!
g0rsq, that is pretty skillful my friend, but at the end of the day, the 1,000,000 pounds question is where the catastrophe starts and why? Will the regular driver/owner understand the schematic?
We are counting on you to find a way on how to re-condition the potential Culprit!
I also wonder if disconnecting and connecting the rear battery will cause any systems to reset and act abnormally?
05-03-2023, 08:17 PM
