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Gents, after starting the car for few weeks with no issues, at one point I noticed a weak cranking action. After doing my research, figured out that the battery is not being charged by the car system, unlike the auxiliary battery which is being charged.
Battery is 4 months old.!
Any hints where to start searching for the culprit?
Thanks in advance for your always timely and wise advice...!
CDK, thanks for the help..! I actually checked where that subwoofer is located and info points to "under the passenger footwell".
I decide to inspect and found that under the matt and the covers, there is a piece of Styrofoam and behind a plate held with 4 nuts.
I wonder if behind that plate which looks like a support for the feet pressure in case of collision is the subwoofer since that doesn't indicated a good location..! And then wonder why they place a fuse in such intricate location.
I think that you may be right about a fuse since the previous owner had a different starter battery that was too tall and he had a piece of plastic trying to avoid contact of the poles with the hood. So, probably he may have had a initial contact that blew a fuse!
CDK, never mind, found a thread with all the ins and outs on this issue plus plenty of photos! I will tackle this job using that info!
Thanks!
There is an excellent chance that the 100 amp fuse will solve your problem. When you remove the subwoofer, and then the round cover which covers the fuse(s) you'll first see the large 200amp fuse. That one is usually ok. The 100 amp fuse which is situated beneath the 200amp fuse is the one which usually blows and produces the specific symptom of the starter battery not charging, but the consumer battery continues to charge.
Guys, I reviewed the PDF titled Dual Battery system, and you are correct, the only link to cause that will be the 100 amp fuse. I found a super nice write-up on another thread from 2015 where they discussed the issue with ample detail and pictures. As soon as I get a chance I get there fully prepared..! Actually, with my starter battery fully charged, I can go two months without any issues! Last time pulled out my compact booster to start the engine..! Frederick, I was in your neighborhood 4 years ago visiting a glass factory and of course the famous Red Light District in Amsterdam.....Nice city.!
There's a fuse in the passenger footwell, behind the woofer. It's a 100A flat fuse, marked F52f1. If that fuse blows, then your alternator can't charge starter battery.
If you have scanner, check for DTC B1829 (Starter battery Circuit Component Fault). It's not an expensive part, but it's a pain to get to it.
Edit: Oops, a little late to the party. I didn't see the other posts answering the question, but yeah, that's mostly your problem.
After I followed the advice of these guys who had the same issues in 2015, I found exactly the culprit....that 100 amp fuse (F52f1) hiding below the 200 amp fuse. It was blown as I suspected. But it is a real pain in the *** indeed to get to it. I am adding a couple of pictures copied from the thread referenced above to alleviate a little bit the pain and add more info. They do not describe that to remove the subwoofer, it is necessary to remove the top cover of the footwell as well as the side trim shown in the picture below.
Also, so you don't waste time finding out the tools to use, I have indicated the fuses nut wrench size. I couldn't find the fuse nearby, so I made one out of .0024" brass shim with a throat .060" wide.! Should do 100 Amp..!
After I followed the advice of these guys who had the same issues in 2015, I found exactly the culprit....that 100 amp fuse (F52f1) hiding below the 200 amp fuse. It was blown as I suspected. But it is a real pain in the *** indeed to get to it. I am adding a couple of pictures copied from the thread referenced above to alleviate a little bit the pain and add more info. They do not describe that to remove the subwoofer, it is necessary to remove the top cover of the footwell as well as the side trim shown in the picture below.
Also, so you don't waste time finding out the tools to use, I have indicated the fuses nut wrench size. I couldn't find the fuse nearby, so I made one out of .0024" brass shim with a throat .060" wide.! Should do 100 Amp..!
hello @elMacko thank you for this write up as I think I have the same issue with my starter battery no longer charging but my accessory battery does.
When you had this issue, did you see the voltage reading on the dash showing 13-14 still or was it much lower 11-12?
My dash voltage reading (there's a couple steps to make this menu come up in the dash) currently reads 12-12.5 and stays there for about an hour and slowly drops down to about 11.5-12 after an hour of driving.
i have the red battery light on BUT no other codes showing up on my Foxwell scanner... i replaced my voltage regulator at 77k miles which was 6 months ago and everything was great then. I had the car in storage from Nov and Jan with 2 trickle chargers on it and ever since is when the charging issue came up.
The voltage at the cluster would be the rear battery. In normal operation, the starter battery runs the starter and then it's only connection to the rest of the electrical system is the charging provided by the battery module (BNS). The alternator is protected by the 200A fuse in that firewall fusebox, so it is possible that you have a bad fuse there. It could also be a bad alternator, but I think that will normally give you a dash warning light. The alternator connects directly to the REAR battery, through that F52f2 fuse.
Thanks @MikeJ65 - I don’t have any codes at all on my Foxwell scanner, but I do have the red battery warning lights on the dash.
Anyone know if a bad alternator throw a DTC code on the R230? Will the BNS or 200 amp throw a code if not working properly?
i’m wondering if this is my alternator because I’ve had alternator (voltage regulator brushes worn) go out on past MB cars but I’ve never seen an actual code thrown because of that.
really appreciate the help here fellas trying to solve this mystery.
I don’t have any codes at all on my Foxwell scanner, but I do have the red battery warning lights on the dash.
That sounds odd to me - I know you can definitely clear the red battery code with the Foxwell. Maybe check again for codes?
Anyone know if a bad alternator throw a DTC code on the R230? Will the BNS or 200 amp throw a code if not working properly?
Quickest way to check the alternator is to check the charging voltage on the rear battery. Should come up pretty quickly to around 14 Volts after starting.
i’m wondering if this is my alternator because I’ve had alternator (voltage regulator brushes worn) go out on past MB cars but I’ve never seen an actual code thrown because of that.
First step is to clear the code and see if it comes back. The red code is a common occurrence, and a low rear battery can throw it.
Then check the charging voltage on the front battery, but know that you won't necessarily always measure a charging voltage on the front battery, but should do so after starting.
Great to find this thread which shows where the big Alternator fuses are.
I've had battery drain issues ever since I bought my 2004 SL600 in late 2021; the dealer even installed a new rear (Consumer) battery in it before I bought it. I really needed to drive the car at least once a week, or it wouldn't start.
As expected after storing the car for two winter months in a trailer with no trickle chargers, both batteries were dead; especially the rear battery which read only 2V. We jumped the car, left it running and drove it for an hour, but the rear battery would no longer hold a charge; its ruined. (Not even after overnight on a 4 AMP charger.)
I therefore decided to chase down the drain. After everything settled down (about 10 minutes), it was still draining 210mA, enough to drain a battery in 2 weeks. I started by removing the 20AMP PSE fuse, but no improvement. I then went through all 78 fuses in the 3 fuse boxes. Removing 20 at a time and waiting 10 minutes, made no difference, still 210mA (.21 Amps).
Until I just found this post, I couldn't find if/where the Alternator was fused. (Some cars use a fuseable link wire.)
So GREAT to find this post.. Next test is to check if the alternator is draining the battery by removing those big fuses. I've read here that it is common for the Alternator's "voltage regulator" to degrade and drain the battery.
Am I correct that this "voltage regulator" is part of the Alternator and to replace it the Alternator needs to be removed?
In the meantime, I just bought an AGM H6 battery from Autozone as I don't want to deal with the MB dealer.
For those curious, the AutoZone Duralast Platinum H6-AGM battery fits perfectly, cost $240 and has a 3 year full replacement warranty.
Note that I have read that some R230 SL may have the bigger H8 battery in the rear, but mine was definitely H6 sized and was MB part # A001-982-80-08. It is 11 inches long.
I really needed to drive the car at least once a week, or it wouldn't start.
That's a flag. You will measure some quiescent current drain from the rear battery, even if there are no faults causing a parasitic drain. This is normal, but you should not measure any current drain from the front battery. The dual battery system is designed to keep the front battery charged and isolated so the car will always start, but you might have a dead or dying front battery anyway that's just not holding charge.
Charge them both back up and measure the current drain from the front battery this time. Something is causing it to drain, either internally it's cooked, or externally via a fault.
The regulator is in the alternator and can be replaced without removing the alternator (at least on the V8, don't know about the V12).
Looking at the circuit, the battery control module would have to be faulty for the front battery to drain, so maybe disconnect that and see what happens to the current draw on the front battery.
Tom, thank you for replying.
Today I determined that the front battery would not hold a charge and I nearly always had to jump it to start. I bought a new one from the dealer; reasonably priced at $237.
With engine running, front battery was being charged at 14.5V, so that is not a problem. IIRC rear also charges fine.
The front battery has only a 8mA (0.008 Amp) parasitic current drain after its initial spark.
The problem is that the rear battery has a 210mA current drain, enough to completely drain a battery in 2 weeks and start to damage it after 1 week.
I found the MB technical document dualbattery.pdf (sorry forgot the URL but Google "R230 Dual Battery On-board Electrical System") with electrical diagrams, parts diagrams, locations, etc.
Since I have already tried all of the 78 "normal" fuses, next is disconnect major components such as the alternator and battery control module.
As documented in many places, this requires accessing F32 and F52 which are in the passenger footwell area. Removing the steel plate (with the Distronic module) and especially the subwoofer box are a real pain. That is where I stopped as unscrewing fuses in such an awkward area is not appealing.
I'm currently inclined to disconnect the battery control module which is in the truck near the battery; others on this forum have reported that this module can also drain both batteries.
Yes, yes, I know I could just connect battery tenders, but I bought this car to work on, which I actually enjoy. So far I have cat-delete, a tune and Apple Car play all working well.
No questions now, I will post an update in a few days, hopefully when I figure out the current drain issue.
The 8 mA draw is probably the battery module monitoring the condition of the front battery. That's the only path back to ground.
210 mA is only 2.4 Watts and might be normal drain; I'm not sure. It's not a lot of current, keeping various modules awake. It's critical to have the right AGM battery in the back, but even with the right battery in good condition (some swear by genuine MB batteries) the consumer functions will start to turn off after a week or so - as reported by many users - and this is normal.
Personally I solved this problem years ago by fitting an isolator on the negative terminal. It's a laughably simple solution and less hassle than fiddling around with chargers. Take everything you want out of the car (as the windows will not lower without a battery, so you can't get back in with the battery disconnected), undo the isolator, put a rag over the boot lock so it doesn't shut all the way and the battery will keep for months.
With the rear battery isolated, the current draw from the front should go to zero but I haven't tested that.
The 8mA drain from front battery is high, but be sure to check what direction the current is. Is it flowing in, or out the battery? I would expect to see a small current flowing in, as the BCM float charges it.
210mA parasitic drain from rear battery would completely discharge a 70Ah battery in just 13 days.
Once the car has shut down and gone to sleep, I would expect to see about 20-40 mA drain, but i have not seen a specific figure quoted for it.
My car has 70mA and I get consumer off line message after about 3 weeks of non use, which I can live with.
2005 R 230 SL350 (M112 3.7). Sold the 1966 W113 230SL recently
210 mA is high, you want max 50-65 mA.
Many fuses are electronic fuses, not the familiar plastic ones, mainly lightbulbs and windows (other components are protected by both electronic and plastic fuses). In theory you could pull all the plastic fuses and still have a component drawing parasitic current.
If you have a rear camera, it could be fed by a circuit protected by an electronic fuse only. So is the glove compartment light... and so on.
Last edited by Frederick NL; 01-20-2023 at 05:07 AM.
Thanks for the additional posts and info. I did not check which way the 8mA current on the front battery was flowing; didn't even consider it. No rear camera.
After spending the 1+ hour getting the steel plate and subwoofer box out of the footwell, I wanted to check as much as I could, including opening the F32 fuse box there.
Here are my results, each after waiting 10-15 minutes for things to settle down.
Starting rear battery drain = 210 mA.
Disconnect alternator via its 200A fuse in the F52 box = 210 mA. (This indicates the alternator's rectifiers and voltage regulator are not causing a drain.)
Disconnect entire F32 fuse box = 67mA. Now we are getting somewhere.
Disconnect 7.5A fuse F89 in truck = 67 mA. So that made no difference.
Reconnect alternative via its 200A fuse = 67mA. Confirms no problem with alternator.
Noticing the Green "emergency release" light in the truck, I disconnect it and it dropped to 34mA. Great. It also confirm that the battery control module N82/1 is not causing a drain.
Reconnect the green trunk light and back to 67mA.
Now time to test the circuits in the F32 fuse box, so reconnect it within the F52 box. (Note that my F52 box has one more wire than shown in the MB documentation - see pictures below.
Disconnect the 3 right-side wires in the F32 fuse box = 67mA. So the 3 left-side wires are not causing the drain. I think this includes the EIS ignition module.
Reconnect the right-most wire = 140mA. So that added a lot of drain. Not sure what this is. (See below)
Reconnect the next two wires which power each of the under-hood fuse boxes. = 210mA. So back to what I started with.
Notice in the MB diagram that the F32 fuse box has 5 wires (1-5), all to the left of the big feed wire. But my picture shows I have 6 wires, including one to the right of the feed wire, and that is the one that causes over 70mA of drain. A smaller red=green wire joins it into a sleeve and I have no idea where that goes. Unless someone here knows what this is, I will research future. I might just disconnect that wire and see what no longer works.
The car is now stored in one of my auto shops and on a tender. I will hook up a meter to monitor the battery drain after a week or two to see if it really does go down after a longer time. I wonder if locking the car reduces the long term drain.
I understand this is all easily solved by keeping a battery tender connected, but I may want to sometimes store it where there is no electrical outlet. I'll just disconnect the rear battery for storage in the future.
Other than why does my F32 fuse box have 6 wires when only 5 are documented, I have no further questions. I just promised an update and here it is. Thanks everyone. Your posts and this forum have been very helpful.
MB documentation of the F32 fuse box on a R230 SL600.
MB documentation of the dual-battery circuitry on a R230 SL600. The F32 fuse box (six wires, not 5) on my 2004 SL600.
Thanks, it did help. It indicates that the right-most red wire is terminal 1 to the M4 suction (engine cooling) fan. That diagram indicates M4 having an electronic module; can't see a reason the cooling fan should draw 1W (70mA x 12V) when the car is sitting with engine long off.
I'll look for the M4 module and try disconnecting it. If that confirms so much drain, I'll look for that module on ebay.
I'll post the result in a few days when I'm at my shop with the car.
2011 S63 , 1997 SL500 La costa edition (sold) 1987 560SEC (sold)
Hello I'm having the same issue as the original poster, however my car is an S63 (2011) I am wondering if anyone knows if I have such a fuse and where would it be located, thanks in advance.
03-24-2022, 09:31 PM
