[V12 TT]

Those ANL fuse blocks were too large to fit discreetly, so I'm glad I ordered a different style as a backup.

Drilled two small holes into one of the brackets that supports the battery, and used plastic rivets to secure the fuse holder caps.

In addition to looking factory, the caps easily rotate out of the way when disconnected from the fuse holder, making the setup perfectly serviceable.

@Tom Manning Thank you for pioneering this. Discovering solutions that are also simple to implement are what make car communities invaluable.

@A1EK Thank you again for bringing another perspective to this. First time I used self-amalgamating tape and it worked perfectly for this application.

View attachment 2887994

View attachment 2887995

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View attachment 2887997

Nice clean install

 

[Tom Manning]

Neat work.

This thread now has 14,000 views and growing, but it wasn't my original idea, I got it from another thread somewhere. MikeJ?

I just wrote it up.

Keep on fusin' out there!

 

[A1EK]

Very nice work, neat and tidy, you have more patience than me !

 

[racox]

nice fuse holders. I got a pair of the ones like in the video.

been reading several of these threads. my problem is battery drain over just a few days to the point car will not start.

watched the video and have looked at the factory BCM flow diagrams that describe the various states.


and to be sure, it appears there are 3 connections on the consumer battery side and two on the starter battery side. one of which is the connections to the K57, correct?


on another thread I got the suggestion to check the 100amp fuse on the starter battery side in the passenger foot well. but after more careful reading of someone having this fuse blown, they get a hard red battery warning and the starter battery does not get charged. if I drive the car every day it seems my starter battery maintains charge. when doing the fuses I'll check continuity on that cable to the starter battery.

only question I have is if disconnecting both batteries at the same time will cause any issues when you reconnect and start/drive the car. on the BCM fuse video he disconnects both, and both are 2004 SL, mine is an AMG if that makes any difference. this may be an issue with the newer MB, but want to be sure.

would appreciate comments on all of these points. need to get my good circuit tester that can check actual amp flow.

 

[Tom Manning]

Sounds like you just have a dying front battery. That's normal after some years.

First check the charge on the front with a voltmeter - should come up to 14V pretty much straight away. If it's charging, the pre-fuses are OK.
Then check for any current draw from the front battery. It should be zero.
If it's not, disconnect all the wires from terminal 30a on the BCM. If the draw stops, then the leak is there.
If the draw remains then pull relay K57. If the leak then stops it's through terminal 30 on the BCM.

But, again, it's probably just a dead front battery, but good to do the testing.

You can safely disconnect both batts. Rear neg first, then front neg.

 

[racox]

thanks for the reminder neg first.

starter battery is NEW. but that does not mean it is GOOD.....

will be doing all those tests when installing the fuses.

 

[aeginc77]

This has been discussed at length at What burns up a BCM? Battery Control Module - MBWorld.org Forums and Battery Control Module rebuild / replacing capacitors but I thought I'd make a new thread as the detail in the header above is easier to find on Google searches.

These fires appear to be a real threat, with many reported instances. Fusing the BCM should provide protection.

First, take the lid off your BCM and look for any burnt components. Mine was fine. They can start to burn up and still work, as you can read in the threads above.

Using information from those two threads, I fitted two fuses in the BCM:

View attachment 2850285

Under the red heat shrink is an M6 nut and bolt which goes to the 30A fuse holder. There are two inputs on the BCM - circuit 30 and 30A. It's easy to see here how it all goes together.

Next I cut this door in the trim (I'll tidy it up later) so I can take the lid off the BCM and inspect it, as well as access the fuses. They should never need to be changed. I insulated the two lugs to the BCM here too.

View attachment 2850286

All works perfectly. I would strongly recommend every owner investigate this mod, for a smoke-free drive. I'll report back if there are any issues but I cannot imagine the BCM drawing anything close to that sort of current in normal operation.
I am preparing to undertake this on my 2005 sl600. Seems simple enough but the first problem I ran into is removing the trunk liner! The MB workshop manual shows this and is complicated. Did you just cut access hole or did you remove the liner?

This has been discussed at length at What burns up a BCM? Battery Control Module - MBWorld.org Forums and Battery Control Module rebuild / replacing capacitors but I thought I'd make a new thread as the detail in the header above is easier to find on Google searches.

These fires appear to be a real threat, with many reported instances. Fusing the BCM should provide protection.

First, take the lid off your BCM and look for any burnt components. Mine was fine. They can start to burn up and still work, as you can read in the threads above.

Using information from those two threads, I fitted two fuses in the BCM:

View attachment 2850285

Under the red heat shrink is an M6 nut and bolt which goes to the 30A fuse holder. There are two inputs on the BCM - circuit 30 and 30A. It's easy to see here how it all goes together.

Next I cut this door in the trim (I'll tidy it up later) so I can take the lid off the BCM and inspect it, as well as access the fuses. They should never need to be changed. I insulated the two lugs to the BCM here too.

View attachment 2850286

All works perfectly. I would strongly recommend every owner investigate this mod, for a smoke-free drive. I'll report back if there are any issues but I cannot imagine the BCM drawing anything close to that sort of current in normal operation.

I am preparing to do this on my 2005 SL 600. Biggest problem I see is removing trunk liner. Did you remove it or just cut access hole?

 

[HLG600]

Neither cutting a hole nor removing the liner fully are necessary, IMO.

Instead, you can remove the fasteners in the surrounding area (and maybe some of the hard plastic trim bits) and carefully fold the panel covering the BCM back.

 

[Makee]

Sounds like you just have a dying front battery. That's normal after some years.

First check the charge on the front with a voltmeter - should come up to 14V pretty much straight away. If it's charging, the pre-fuses are OK.
Then check for any current draw from the front battery. It should be zero.
If it's not, disconnect all the wires from terminal 30a on the BCM. If the draw stops, then the leak is there.
If the draw remains then pull relay K57. If the leak then stops it's through terminal 30 on the BCM.

But, again, it's probably just a dead front battery, but good to do the testing.

You can safely disconnect both batts. Rear neg first, then front neg.

Tom, I migrated from the MBworld forum to this one trying to find answers and information..! I can tell there has been a lot of discussions on BCM fires and failures and how to protect it. I am just going to drop my two cents of contribution.
Two weeks ago just when I was parking my SL-500 in my garage, I perceived a "burn electronic" smell while the red light battery came on in my cluster. I immediately move around to see where the smell was coming from, and was from the trunk. I disconnected the rear battery and started troubleshooting. After few motions and scanning, decided to inspect the BCM. Removed it and opened the lid to find out that under one of the capacitors the board was burned. I had 100 amp fuses on 30a and it was intact....meaning that this kind of failure I had probably was caused by a current less than 20 amps! So there goes the fuses on 30 and 30a protection. I certainly agree that these could prevent a catastrophic burn out preventing the cable from the AGM battery being shorted to ground inside the BCM, which is what burns cars..! After I got fully convinced that I would need to shed north of $1000 for a replacement BCM which could fail at anytime again, I have decided to find the way around the BCM. I already placed my partially burned BCM on the vehicle to find out what functions are still available. I also separated the starter battery from the BCM and connected it to a DC to DC charger which feeds from the terminal 30. In this way my starter battery is always charged. The vehicle now runs fine with no radio, but I am in a journey to determine which functions of the BCM I could bypass to restore full functionality and get rid of the BCM completely!

 

[MikeJ65]

Did you have a fuse between the battery cable and the 30 post on the BCM?

 

[tallguy2020]

...someone will eventually come up with a play and play (pray) solution for this, thinking China? Maybe I am wrong, maybe the market would be too small for it to make sense?

 

[racox]

Tom,
thanks again for your reply. makes total sense from research I have done.

Makee
your post is somewhat confusing. As Mikej65 asks, did you have a fuse on the 30 side of the BCM? I am about to install the 30amp fuses on both sides of the BCM. from reading threads and studying the schematics if appears the highest risk if from the alt/consumer battery on the 30 side of BCM. it appears only power source on the 30a side is the starter battery.

 

[V12 TT]

Just finished this morning. Not the most inconspicuous by any means but I want a window so I can check the BCM from time to time. I also wanted a hard mounted connection / bulkhead for the oem wires. Question - the fuse holders came with mini anl 150 amp fuses, are these ok or should I switch to 30 amp? If the BCM grounds it’s gonna throw a lot more than 150 amps from the rear battery and pop the fuses rights ?

 

[V12 TT]

Going to make cf covers to cover the holes in carpet I have for coil over adjustment.

 

[MikeJ65]

Go to 30 amp, might make the difference between a rebuildable BCM and a totalled one. Not worth saving couple of dollars to stay with the 150's.

 

[aeginc77]

Just finished this morning. Not the most inconspicuous by any means but I want a window so I can check the BCM from time to time. I also wanted a hard mounted connection / bulkhead for the oem wires. Question - the fuse holders came with mini anl 150 amp fuses, are these ok or should I switch to 30 amp? If the BCM grounds it’s gonna throw a lot more than 150 amps from the rear battery and pop the fuses rights ? View attachment 2889549 View attachment 2889550

Nice job! What will you make the covers out of?

 

[V12 TT]

Nice job! What will you make the covers out of?

Thanks, carbon fiber sheets

 

[V12 TT]

Go to 30 amp, might make the difference between a rebuildable BCM and a totalled one. Not worth saving couple of dollars to stay with the 150's.

True, already ordered the 30amp fuses

 

[HLG600]

Nice job. I decided against cutting the carpet, but your approach to it looks clean.

Good move on scaling down to 30A fuses. We want these fuses to fail at even the slightest spike.

It's going to be nowhere near 30A of course so I think I can safely drop the fuses down to 15 or 10A. We'll see.

Speaking of which, have you tested any fuses < 30A yet?

 

[Makee]

Having pored over the circuit diagrams (I'm a electronics engineer) this looks like a very sensible idea. 30 amps, shorted to ground, is of course plenty to cause a fire in any case but it seems likely that if the BCM had some sort of catastrophic failure then much more current than that would try to flow. As such the fuse would die hopefully before things had got properly hot.

Great stuff.

Teem50, I already have a partially burned BCM under one of the capacitors, have been studying these electronic diagrams to see how some functions could be bypassed, a portion of the consumers (radio and roof) are disabled, so, by trials I have eliminated the BCM connections with such "disabling function" to terminals 6 and 7 from the ECM. These terminals connect to CAN B which for sure are responsible for transmitting encoded messages to the CAN bus. Since you are an electronic guy, how could I interrupt this encoded message or remove it from the ECU to enable consumers without the BCM interaction?
Thanks for sharing your wisdom!