Maybe someone can give me some direction. Since I have been working on this car for the last 3 months the red battery warning lamp has been on. I am not sure if it was on when I got the car about a year ago because the car was inoperative.

I replaced the rear/auxiliary/consumer battery about 3 days ago but the warning lamp problem was before that. Just fyi, that battery would not hold a charge. BTW, I have NEVER jump started the car. Just used a quality charger.

I have tested both batteries this morning below are the results.

With car off (and after it set over nightz0:
Front/Starter battery: 12.65 V
Rear/Auxiliary battery: 12.71 V

With car running:
Front/Starter battery: 14.00 V
Rear/Auxiliary: 13.85

The iCarsoft says charging is at 13.79 V but it does not allow to check at each battery so I assume that this the alternator charging voltage.

Any suggestions on where to start looking?


This is with car running.

FYI, the SRS problem will be addressed in a different thread.

Thanks.

 

Experiencing the same issue, subscribed to follow. I have confirmed both batteries are 100% operational and have cleared the codes (which return)
I have seen many threads in this so will be searching as well.

 

Bob, it's likely that your '04 model has the original BCM with the factory design flaw, which unfortunately is a fire risk.

Need to remove and inspect it, as well as load-test your consumer battery.

 

Thanks for the comments. That BCM unit is right in front of the accessory battery correct? Short of it catching on fire, which I am aware of, what would it do to throw that battery warning light? Should I just go straight to replacing it? And I do understand the load testing comment, but I just put that battery in 48 hours ago.

Thanks

 

I believe one other thing to try is reset the code with a proper diagnostic tool. This didn’t work in mine and ended up being the battery control module. Mot than likely that may be the issue.

 

13.85 is a little low as well, and the 14.0 should be a little bit more. The voltage regulator could be suspect. Welcome to the Rube Goldberg Mercedes electronics, it’s quite a nightmare.

 

Thanks to everyone for the comments. Boy, I have been reading Brian Wallace’s information about this on his Facebook page. It looks like the safest bet is going to be to replace the BCM. So that’s not particularly inexpensive but I guess it’s better than a fire. Lol.

I am still wondering however in the meantime if there is any “maintenance“ that can be performed on the original type BCM. Thanks

 

Not that I know of, it either works doesn’t work or burns up,

 

Woah, first try to clear the code out with your scanner and see what happens.

It's common to get the red warning light after a rear battery change, and it's common to be able to clear it successfully.

If that works replace all the electrolytic capacitors in the BCM and fuse the terminals before you rush into replacing it.

 

I disconnected both my batteries for 8 years on 2 cars and never had the battery light, so I wouldn’t consider it common. I would certainly try to reset with the proper tool. If you are going to continue owning this car, you are going to need a decent to good diagnostic tool for attempting to diagnose issues.

 

Well, this was helpful. To say the least! I went in with my iCarsoft and found the module and cleared the fault codes. And the red battery light went away. But it wasn’t under BCM as there is no BCM on the iCarsoft. I will take a look tomorrow and see just how I found it. By the way, driving the car later on tonight it did come back on for a short time and then went out.

 

You're doin' the Charleston now in Charleston now, those codes can be a bit panic inducing. That code is generated from the BCM so your scanner is likely scanning all modules in turn, just not listing where they are on the car.
If the rear battery goes low it can generate the warning, just disconnecting and reconnecting a good battery shouldn't throw the code.
Fuse mod has been discussed at length https://www.benzworld.org/threads/fu...-fire.3129614/
As a priority now I would pull the module and replace all those nine caps, they leak on to the board and short it out. There could still be a fault with the BCM but first rule out a suspect battery, they can be faulty from new.

 

Similar to others, I would start with a scanner to reset those codes and see if that solves the Red lights.
And yes, 13.72 volts is low, it could indicate an alternator problem. Since the alternator output is controlled, I guess the BCM could be causing the low output voltage.
IMHO, I would only fuse the BCM and not replace it just yet. Once fused, it cannot catch on fire, although it can internally deteriorate.
OR do the experts suspect the BCM is causing the low alternator voltage? (I'm still learning about these failures.)
There are videos on how to access the BCM on YouTube; one guy disassembled the entire trunk area; another just pulls the carpeting aside. I tried to pull the carpeting aside after an extensive partial disassembly and still could not. I ended up just cutting an upside down "U" flap over the BCM which make it and the new fuses easy to access. I plan to post a new thread on this, but can send you a pic of the "U" flap position now if you like.
Note that used BCMs, of unknown quality, are $2000 on ebay. As suggested, it is often better to send your BCM to a special repair shop which replaces the capacitors and anything else, as long as it is still in reasonable shape.

 

Tom, I’ve watched two YouTube videos where they show how to make the fuse cables. I was wondering if there is anyone out there who actually sells a kit.

 

Probably not, but if you look at the first picture on the thread https://www.benzworld.org/threads/fu...#post-18666667 you can see under the heat shrink it's just nuts and bolts on to a suitable round terminal so very easy to make. You could probably - certainly - crimp it all with a crimping tool if you're not confident soldering.

 

On Amazon search for "automotive inline fuse holder" which come with leads onto which to crimp. 12 or 14 gauge is fine. If you need 30A fuses, some kits come with fuses. All for under $10.
You will need 2 yellow spade crimps for an M8 bolt and 2 more for M6 bolts. On Amazon "Kuject 320PCS Heat Shrink Wire Connectors Kit" is a huge overkill, but likely not much more expensive than buying a few at the local parts store.
I suggest relatively large heat shrink tubing, instead of just electrical tape. Search Amazon for : automotive heat shrink tubing 3/4"
Knowing a little about you, you already have such crimps or can use a refill kit.
Disconnect the two heavy wires to the M8 bolt on the BCM and connect them to one of an inline fuse with the larger spade crimp. Protect with heat shrink tubing. Other end also has a large crimp and goes to the M8 bolt on the BCM.
Similarly for the medium and smaller wire to the M6 bolt on the BCM.

 

I would immediately take the rear carpet out. Remove BCM. Take it apart. If it's not melted inside (mine was), it can be repaired($200-300). There's a place in Tampa, that's receiving 20-30 a month to hopefully be repaired. If melted, your best option is Brian's on Facebook for around $600. I've had that on min e for about 4 m months and no issues whatsoever. I don't even have to have a charger hooked up anymore. Your other option would be to buy a used for $2000-3000 on Ebay and probably have the same problem again or, worse, buy someones unrepairable one.

 

Yes, this seems to be the standard response. I had a text with Brian yesterday. I told him about the K57 fault. He said I should go ahead and replace that relay and “go ahead and replace the other one too.” I text back and ask him to clarify what the “other one“ was and where it was. But he hasn’t responded and it’s been way over 24 hours. Does anybody have any idea what this “other one” is? Is it maybe the K 57/2 that I have seen referenced another post? I can’t find any information on it, what type of relay it is, or where it is. Thanks

 

Maybe a little progress on this end. I have fully removed all the carpeting in the trunk. I have inspected all of the areas around the BCM and I see no signs of moisture or remnants of previous moisture. I took the BCM out and inspected the outer casings. I was kind of amazed to find that there’s no gasket between the lid and the body. I carefully smelled around and noticed no sign of any smoke. I also looked at all the internal parts and saw no signs of any electrical shortages. I use the magnifying glass and scrutinized very well. So back to some original symptoms. The same single code is always thrown. Fault detection with K 57 Component relay. I have replaced the relay twice. That has not changed things. The only thing that has changed is that now if I charge the battery overnight or if I drive the car a fair amount and cut it off and then very quickly restart it it will not throw the code.

also, I took a battery from another vehicle that I had charged overnight and jumped it to the starter battery. It seems that the voltage/cranking amps from that battery would allow me to start my car over and over and over without throwing the code. That’s pointing to a battery that is right on the edge of going bad but still never fails to start the car. So now I am suspecting that the battery and voltage regulator are not giving an adequate charge or that the starter battery is slightly below the voltage that K 57 needs to detect. I have replaced the consumer battery. My most recent values for the value of the batteries are: After sitting overnight the starting battery is showing a resting voltage of 13.8. And the consuming battery is showing a voltage of 13.7. With the car running the voltage at the starting battery is 14.6 and at the consuming battery 14.4. As the consuming battery is brand new I am assuming that the starting battery is somehow culprit and the voltage is dipping just below the threshold to set off the fault. And this is happening on cranky. Hence my test with the jumper cables and another battery. I’m going to go ahead and replace the starting battery tomorrow and for good measure I am going to replace the voltage regulator. Does anyone have a strong opinion on what voltage regulator I should get? And as usual, any comments will be appreciated.

 

Not a bad idea to replace the front battery regardless, but a failing starter battery won't necessarily throw a code.

For the regulator, get a Bosch but beware of counterfeit parts floating around.

 

Tom, I did replace the starting battery with a high-quality Interstate battery that is actually labeled for use in Mercedes. I checked the voltage on the battery when I got it home and while still not installed in the car. I got 12.85 V. I went ahead and put a charger on it overnight just to be on the safe side. I installed the battery and when I cranked it the red light and the component 57 warning did not come up. I checked the charging voltage with the car running and both were in the appropriate range. But after driving the car for a while, turning it off, and then turning it back on the warning light came back on again. This procedure is repeatable. In other words, giving the battery a charge for some reason eliminates the fault code with the initial start but the fault code returns after that initial start. To be fair, the fault code will not appear if upon initial start I restarted a few times within a very short period of time. There is something about letting it set that seems to trigger the problem. As the charging values seem to be above what people are saying are acceptable it looks like it’s going
to be replacing the BCM unit.

 

I wonder if the BCM has aged and is now reading the battery voltages as lower than they really are. In other words, it reads 12.85 as fine, but perhaps 12.7 as low, when anything above 12.25 should be considered fine.

 

I think you are right here. And that has been my thinking as I have indicated in previous posts. There seems to be some super fine line in the voltage that triggers the fault. And the fine line seems to be way above what would be considered normal for voltage readings on start up. And then it does not make sense that the charging voltage while the car is running is very high. I’m not sure why that wouldn’t bump the battery up past that suspected critical ultrafine line.

It looks like I need to get in the upgraded BCM line. I do appreciate what it takes to make that product but it is a bit expensive. I’ll check with Brian and see what the ETA will be.

 

Where did you find it on iCarsoft, I can't find it

 

Hi Bob.It might that you have the same problem as I have with my SL 55 AMG 2002 mod.
The BCM nearly caught fire, and there was a big short circuit in the BCM.
I’m now looking for a new, or rebuild, CAN ANYONE GIVE ME SOM INFO ON WHO, WHERE?
PS, You should disconnect both batteries, find the BCM, and open it, It might look like mine.
I have attached some pictures showing what my BCM look like.