Dreaded Red Battery Icon - How I Fixed It
 

I know that quite a few R230 SL owners have been stymied by the dreaded RED battery icon. I was able to fix the problem without the #*&$ MB dealer service department. Here is my story:

In late August I went to start my 2008 SL550. I stepped on the brake, pressed the start button and got… Nothing. No clicking, no turning over, just dead silence. Both batteries were the originals from the factory and the starter cranking had gotten a little weak in the previous month, so I largely expected this. Seven years seems like pretty good service from the factory batteries, in any case. No problem, I thought, I’ll just jump start from my minivan via the SL's starter battery terminals, go buy new batteries, do the installations and my problem will be solved, right?

The next day I bought a new starter battery from the local MB dealer and a new AGM trunk battery from my local auto parts store. I already knew that the starter battery was a unique MB item, so I paid the $$ to the dealer parts department. The non-MB AGM battery that I bought for the trunk (an AutoCraft Platinum AGM Battery, Group Size H6, 760 CCA) appeared identical to the original and cost about half as much as the MB version. On the way to the MB dealer, I noticed for the first time the big RED battery icon lit on my multifunction display. No surprise, I thought, I just needed to get on with replacing the batteries.

Once home, I fully charged both batteries using my CTEK Multi 3300 charger. I then installed both, connecting the starter battery first as recommended, then the AGM trunk battery. The AGM battery fit like a glove in the trunk. So far, so good. The engine started normally. Everything in my beloved SL worked just like before EXCEPT for the RED battery icon that was still on the dash. I read some online advice that said to keep driving and it will eventually disappear.

The battery warning icon never quit. I could scroll the display and it would go away, but the next time I started the engine it would be right back. I checked both batteries with my voltmeter and found both apparently healthy at about 12.4 to 12.5 volts. However, with the engine running I found good charging voltage at about 14.4 volts on the trunk battery, but the starter battery was still only at 12.4 volts. The N82/1 control module in the trunk is supposed to ‘optimize’ starter battery charging based on temperature and voltage. So, I thought that perhaps it was charging the starter battery, but just not when I checked it.

I wanted to catch the starter battery in the act of being charged, so I wired the battery to my voltmeter, taped the voltmeter to my dash and patiently watched. I watched for the next two weeks (probably over 20 trips). The voltage would dip for less than a second while starting then return to 12.3 - 12.4 volts. I finally concluded that my brand new, fully pre-charged, starter battery had been starting my car for ten weeks without ever getting any juice from the N82/1. The alternator was not a suspect because it was charging the trunk battery just fine. The attached schematic suggested that either N82/1 box was bad or F52f1 100 amp fuse was blown. Of the two, the fuse would be a lot (like $800) cheaper to buy, so I went for the fuse.

Accessing F52f1 in the passenger side footwell was made much harder by the huge plastic sound subwoofer installed there (that’s a whole story by itself). My Star Manual disc was no help, as this US optional Bose equipment is not even mentioned in the manual.

The fuse, a Blue Sea 5256 MIDI/AMI 100 Amp Fuse is barely accessible, but cheap to replace. After removing the passenger-side carpet, a black styrofoam panel, a metal protector panel, the big black subwoofer assembly (which required a 10mm DEEP SOCKET), the 'fuse through-plating’ cover, AND the larger F52f2 fuse, FINALLY I had my fingers on F52f1. I removed it, tested it and sure enough, it was blown. I am pretty sure that I unknowingly blew the fuse when I jump-started the car months earlier.

Everything is back to normal now. The starter battery is getting a healthy charge from the N82/1 and the big RED battery icon went out and never returned.

Thanks for the writeup. Good troubleshooting.

CPDay -- Thanks for your post.

I'm having the same problem. I recently replaced my convenience battery (two months ago), but the red battery light stayed on. The dealership told me it should reset after a few starts, but it didn't. I just had my oil changed and asked about the battery light. I had to pay $155 just to have them run a short test, which they said couldn't connect to my front passenger SAM. Drove home from the dealership with no problem, but the next time I went to drive, she's completely dead! No lights or anything.

I haven't changed the rear battery ever since I bought her in 2010. I read online that a weak battery could affect the SAM. I'm taking the rear battery out to have it checked/replaced if needed. I also want to check the fuse you mentioned, F52f1. Can you advise it's location looking at your third picture. Also, if the fuse doesn't fix the problem, the dealership wants $900 to replace SAM. I found the SAM on eBay from an SL550 with 23000 miles (mine only has 45000 FYI). Will I be able to switch them out myself without needing dealership to program it?

Thanks in advance!

thanks for the writeup..
i have a SIMILAR issue but probably not the same cause..
i'll go looking for that fuse, though..

where did you get that circuit diagram..?

thanks,
bill morrow

One thing I learned from this experience is that getting to the two fuses in the passenger footwell is a major pain in the neck. It is made much worse by the (largely-undocumented) Bose subwoofer design. Give me a day or two and I'll try to add some pics and descriptions to help.

Here's a link to the source document that answered many questions:
http://www.benzworld.org/forums/atta...battery-system

So my key fob was fine but my rear battery registered 6 volts after being out of the car for a couple days. I bought a new AGM and charged the starter battery and she fired right up. Only problems is that the red battery light is still on. I connected the starter battery first, then the rear battery. The good news is that my convenience functions are no longer unavailable!

Now I have to check the fuse CPDay mentioned or I have a bad SAM???

regrettably that document, while really excellent, does not help getting the <expletive deleted> bose woofer out of the foot-well..:nix:

I Promised More Info. Here It Is:
 

The trickiest part of replacing the fuse in question (F52f1) is digging through the passenger footwell layers to find it. This is all complicated by the optional Bose subwoofer installation. There are several layers to dig through: The carpeting and carpet pad, a styrofoam panel, a ribbed metal panel, the plastic subwoofer box, the plastic through-plating cover, and finally, the larger F52f2 fuse (which engineers unfortunately decided to locate directly over F52f1, covering it).

After all this digging, the MIDI/AMI 100 amp fuse can be tested and/or replaced. If it is blown, then that is at least one of the problems. It was the entire problem in my case and eliminated the red battery icon. I took some photos during the operation that should help and are attached.

Some key points:

The carpet and carpet pad need only be rolled back toward the passenger seat, not fully removed. The nuts tend to roll out of sight under the carpet pad, so an inspection mirror is handy for finding them.

There are three 10mm nuts securing the subwoofer box. Two plastic ones are easy, but the third, metal one is in a deep recess. I needed a deep socket to reach over the the long threaded stud and extract the nut.

The speaker wires are easy to disconnect via a small, white, clipped electrical connector.

The 'through-plating' is the thing that contains the two fuses. Be deliberate and patient when moving cables and removing the black through-plating cover. The cover was tricky for me to replace properly.

Magnetized tools can help on the small nuts that hold the fuses. Otherwise they can be easily lost.

A good work headlamp was a great help.

thanks for the pix and your work in documenting the fuses, etc..
a quick question, how does that woofer come out..?
does the top edge rotate out or the bottom edge rotate out..?
each rotating from the other edge..

and FWIW, this has been worked on before since the carpet padding shows scuffing and small tears and the fuse box cover is missing..

edit: juggled the woofer out from the bottom, then some twisting and finally success except the fuses are intact.. 12.7VDC present on both sides of both fuses..
what a place to located fuses.. Daimler-benz might have better placed them under the intake manifold to better frustrate owners and mechanics

Bill Morrow-

Make sure the speaker wire is disconnected first.

Once the three nuts holding the subwoofer box are removed, pull the right side of the box off of the threaded stud sticking up into the recess. Then shift the box up and to the right to get it off of the two remaining threaded studs.

Bill Morrow-In your situation I might have removed and tested both fuses individually. If you look at the schematics, I think that you'll see that all 4 points may be 12.7v from ground even if one fuse is blown, depending on what the N82/1 is doing as it tries to balance the dual batteries.

This is great detailed information. Thanks for all of the contributions. Now that winter has hit Michigan I may jsut wait unti lthe spring to work on it when it is warmer. I will put a trickle battery on both batteries for the winter. Thanks to all

you might be right..
to get the fuses out might have been more than i could physically do at that point..
and now i've about had it and i'm going to have a serious chat with the dealer i bought the car from..

Very useful info!!!
I've learned a lot from this.
moretech

I'll be tackling the fuses tomorrow. I'll report back then. Wish me luck lol!

djbadeaux:
you'll need 10mm sockets.. most everything is a 10mm nut..
for me, i folded the passenger carpet back, removed the styrofoam board, unbolted the metal plate, spent some time trying to wrestle it out of the restricted space it occupies, invented some new curse words, resisted the urge to fling metal plate across garage, unbolted woofer, more wrestling and cursing, went to bed, next afternoon resumed wrestling match, pried woofer up from bottom left edge (don't forget to unplug speaker wire on bottom right edge) got bottom left attachment point past folded carpet/foam padding, more wrestling and cursing bose and daimler, finally success as out it comes with no damage and only a few small tears in the carpet padding..
the cover on the round fuse box was missing on my car, so there were the fuses..
and attached is a picture..
https://cimg0.ibsrv.net/gimg/www.mbw...7ba37a2df4.jpg

cordially,
bill morrow

Good photo! It's interesting that your F52f2 (the 250amp fuse) has a clear cover. It can be seen that it is not blown.

Unfortunately, F52f1 (the 100amp fuse that was my problem) is underneath F52f2 and cannot be clearly seen or accessed. It's kind of a thoughtless design.

Neither of your fuses look like originals and your black through-plating cover was missing, so do you conclude that this has been problem area for a previous owner?

yes..
it is too bad i could not see the other fuse..
by this time i had won the one battle and figured to just button it up and let a dealer do his thing..
the car dealer i bought the car from has agreed to pay to fix this so....

and yes, it is obvious this has been done before.. the cover is missing.. the padding under the carpet shows signs of this as well..

cordially,
bill morrow

Sorry guys, I got caught up in a "honey do list" before Thanksgiving... and maybe a little brandy eggnog, but will update as soon as I sober up and tackle the fuses. Thanks for the advice and pics. I'm glad to see I'm not the only one that doesn't like being bent over at the dealership...

IRT BOHICA..
an old navy term..
as in bend over here it comes again..

there was a really nice ex-dealer tech who had a small shop a couple of miles away..
very nice guy, knew his stuff and did not feel he had to make his first million from ME..!
he even would come here, jack up a car, roll under it and 40 minutes later the new conductor plate was installed in the S600 tranny..

he once told me that some/most/all dealers have their tech come in to work, bid on each job that was there, do the job for whatever they bid it in at and then move on to the next job..
they got about $35/hour for the time and the dealership charged at $125 or more an hour "book" time for the job..'
so that conductor plate that cost me $50~ for the part, another $30~ for the gasket set, maybe $30 for new oil and $50 for his time.. yes $50..!
what is that..? under $200 for a job the dealer would have charged near $1k.. with the conductoe plate at $200~ retail for a part that is common to some jeep and other chrysler tranny's and is avainable for $20~ to $100~ all over..
("~"=more or less)

his wife divorcing him put an end to that happy time..
just when i need him to deal with the S600 and its V12 usually but V10 occasionally..
and no, it has new coil packs, new plugs, ne wiring, new lots of stuff that will now wind up in the breaking yard..

so my suggestion, when visiting a dealer shop, know what is going on and get bids on the job..

mercedes is a fine car with the unhappy reputation of being very costly to repair.. with astronomical part costs..
i wonder what cadillac wants for a new starter battery..?

if daimler had ANY sense at all they would publish all their repair manuals, repair videos on youtube and do everything to help owners of elderly, mature and ancient mercedes cars to help owners keep those cars on the road..
mercedes would also do everything in their power to help indy shops deal with the esoteric ailments expecially of the 2000 to 2003~ electronic gremlins that plague those otherwise wonderful cars..

occasionally i ask myself why i bother when a ford sedan would do just as well for the driving i usually do and any gas station mechanic could fix it..
but then, i've been driving mercedes since 1970 and except for my big ford f350, a cadillac allante and a lexus sc400 ONLY mercedes..

sorry for the mild fulminations, and back to the topic at hand.. :)

bill morrow -

Fulminations??? I actually had to look that one up. Thanks for the addition to my vocab. I couldn't agree more. I've been working in the sales and finance mgmt side of the car business for 8 years now. My 2007 SL550 has been adequately taken care of at my KIA dealership (by a former Mercedes mechanic) since I bought it in 2009. The only thing we cant do is the SDS diagnostic obviously. As mentioned above, my last oil change cost an additional $155 to plug in their software for 5 mins, only to tell me they couldn't connect with my front passenger SAM. However, that may not be the issue. For $987 they would replace the SAM and continue diagnosing the problem. I don't have an issue with a dealership recouping costs for equipment, but damnit tell me your gonna fix the f'ing problem. Don't tell me you're gonna charge me x amount and that SAM replacement might not fix the problem. I drive a Mercedes because I feel good when I drive it. And I'm willing to pay a premium for that feeling. I just don't like being f'ed!

i JUST NOW, took a risk, and, for $730 ordered a star diag system, ver 2015.9..
from here: http://www.auto-repair-tools.com/who...&category_id=0

we shall see what we shall see..

but a man without tools is just a monkey beating a coconut with a dull rock..

i'll try to let you know what i get & how it works..

no one whats to bankrupt a good dealer but on the other side of the coin, no dealer should bankrupt his customers..

you're welcome for fulminating.. the smilie: :wall: might work but i think i have a better one on my forum.. :) red with flames shooting from mouth..

My thanks go to Bill Morrow and djbadeaux for contributing to this thread. It's not just about the red battery icon, is it? Our bigger issue is the very poor job Mercedes does in documenting their products and supporting drivers of cars over a few years of age.

I've maintained a long, long line of Toyotas, Subarus, Mazdas and a Mitsubishi 3000 GT (that one for 21 years!). I never had the frustration that I have had maintaining three MB products. I live 150 yards from an MB dealership and I absolutely REFUSE to go there for anything other than a part that I can't buy any other way.

Bill Morrow - Please share your experience with the Star diagnostic system, both the purchase and the use. I am about to do the same.