Ever since I’ve owned my 2006 CLS55 AMG I have intermittent dead battery. It would be fine for months and then the “two day” cycle would start. First day battery would start but say convenience functions not active to to low battery. Next day dead. Drove myself nuts and finally tracked it down to fuse 29 drivers side which controls the ignition. Pull the fuse and no problems. But it is intermittent. Either bad ignition or relay sticking. Has anyone had similar issues? Thanks in advance.

 

These cars are becoming a real pain in the *** with parasitic battery drain. All this generation of Mercedes seems to be starting the unknown battery drain.

 

It does seem inevitable though usually it's a module that needs to be replaced. My 04 has no drain issues, other the one I resolved early in my ownership which was due to the front SAM getting wet.

 

Hi guys, Apologies if this isn't the right place to post this. I need help, I'm really lost as to what could be causing huge battery drain. I have a 2002 E270 cdi. Its had its issues over the years, new head gasket, new SBC, recon'd turbo etc, but electrically its been fairly ok. What i did notice over the last few years is if i didnt use it for 3 to 4 days the battery would only just start it. I replaced the main battery on 31/07/2020 but it still did same thing. i suspected the regulator wasnt charging the battery properly so put a new one in 10 days ago, car has been normal, starting every morning no problem. 3 days ago i decided to check all my fuses and found a few blown, i cant remember what ones they were exactly but i replaced them, i do remember they were 2 of the bottom 4 or 5 fuses in the boot / trunk rear left fuse box and i had a blown 15amp in front fuse box under bonnet/hood which controls EGR etc. That evening i went to the jet wash garage and washed car with car music playing for 15mins, went to start car and it was dead. jump started it, got home. Put battery on charge at home, charged fairly quick and i put it back on car. Next morning battery dead. After lots of googling i started doing tests with a multi meter set to dc.

I removed the main battery negative and put multi meter in series (from neg post to cable) it read 11.6v, i thought maybe bcm faulty so put meter from battery post to chassis, still 11.6v. I put car to sleep locking all door latches waiting half hour then removed main battery neg terminal then put multi meter in series again and pulled each fuse one by one looking at meter each time for drop, nothing. i pulled every fuse on car on all 3 fuse boxes one by one, each time checking meter, still sat at 11.6v. I then reconnected battery and tested each fuse with meter, none had any reading (0,1 / 0,0) . I then did a continuity test on all the relays, all good.
I re charged the battery, started the car put on heater, stereo, window heaters, lights and tested the main battery to see of it was charging ok, all seemed good, was getting 13,5 to 14,1v which leads me to believe alternator and regulator ok and charging battery correctly.
All these tests were over the last 3 days and charging and discharging the main battery so many times has ruined the battery, now it says its fully charged but when i put it on car it barely turns it over. So i had to go and buy a new battery today, but i'm still getting the crazy 11.6v drain. What would be using that much power ??. I disconnected all the fuses that run the (aftermarket) stereo, still drain, and i disconnected the seat control module, still drain. I'm now thinking about removing ALL the fuses in the car, see if the drain drops, then replace them one by one to see when it reappears.
I've had the car 4 years and this has just suddenly happened, oddly enough the day i was replacing the blown fuses.

 

I had the same issue but with a different model. I followed every diagnostic sequence as I think you have too. Finally I took the car to a MBZ shop and they diagnosed it as a bad SAM. Once the SAM was replaced, the issue was resolved. I am no expert on these issues, but my 2 cents worth.

 

Yes in my case the fix was to replace the windshield cowl and get the later model cover for the SAM. Once I did both of those things, I never had the issue again. I figured it out after I correlated the issue to getting wet. I also realized that it was acting as if the ignition switch was on (red indicator next to P on the shifter would stay on even though the car should have gone to sleep). I think I had a code for the EIS circuit 15R being hot or something when it shouldn't be, which is done inside of the front SAM. And in my case there was one more clue that I didn't understand: a previous owner had wired the intercooler pump to an ignition hot source. So when I had this problem, the intercooler pump would also run continuously. That did a number on the battery as well. Eventually I had to replace the battery after fixing the issue and again, haven't had a drain issue since. Wet, or dry.

 

Thanks guys, thats been a big help in narrowing down the problem. I'm going to remove the back sam (fuse box in trunk) to look for corrosion and inspect the front. I do know that the rubber seals on both sides of my trunk are cracked, and the front windshield cowl is cracked and split in places....(more items on the replace list......seems to be never ending). Is there a way i can test to see which sam is faulty with a trusty ol multi meter (its all i have hehe) or will i need to take it for diagnostics to find out which one. does it have to be a star diagnostic or can a street garage diagnose it. Seems that here in my part of Spain only MB dealers have star and they charge half a kidney per day......(so i've heard).

 

I would start with a cheap tool that can scan all modules for codes, like the iCarSoft MBII. That's what tipped me toward the direction of the SAM and ultimately research about water intrusion issues. I never "saw" any issues with anything. Obviously if you find a SAM sitting in 6 inches of water that's pretty conclusive...but that wasn't the case for my situation.

 

I've been thinking for a while that i need a diagnostic tool and i think its time to get one, it's all spend spend spend, haha. Thank you again for your help.

 

The iCarSoft is like in the $150 range. I suspect there are better options though.

 

This could be your problem, check it out. This dude is pretty sharp.

 

Hi, I'm a newbie here and I read your post and the other one before it with interest. Can the MOST module be completely disconnected?

Here's my situation: We have a 2003 S500 4matic with some sort of parasitic battery drain...it keeps draining down the battery after a couple of weeks of not being run. Neither a Battery Tender nor a Duracell equivalent can prevent this from happening. When it does, I must disconnect the battery and use a 10amp charger to charge it up again--this is at least the 3rd battery in the car. My eldest son used to use it, but when he went off to college it didn't get driven as much.

Several years ago, the radio/entertainment/phone head went bad. An audio shop installed an Alpine head to replace it that handles radio, CDs, Blue Tooth, Pandora, backup camera, hands-free calling, and Nav. As long as the car was driven regularly there appeared to be no problem.

I have had the car to two separate shops that specialize in European cars and all sorts of higher end vehicles. One was actually formerly a certified Mercedes mechanic! Neither could find the parasitic leak.

I have 3 possible culprits that I know of:
1) Something you said about the MOST module makes me wonder if it's continually hunting for its own Mercedes components, draining power at unobserved times. The CD changer is still in the trunk, and the phone mount is still in the center console. I have no idea where the Nav unit is...but the head is on the floor in a corner of my garage.
Can the MOST module be removed or power cut to is because it no longer, as far as I can tell, doing ANYTHING useful that the Alpine head isn't?

2) A recent failure that I didn't know about until a couple of days ago was the Driver's Door Control Module. AFAIK, it was fine but when the 2nd shop picked it up (I wasn't home) the driver couldn't adjust the mirrors, seat, seat heater, etc. I tested the Brown and Red/Black wires, pins 1 and 2 and directed and there was no resistance to ground from the Brown wire and 12v from the Red/Black one, indicating that the DCM is probably bad--I have a used one on order. I gather that, too can be the source of a parasitic drain.

3) The air suspension system has a slow leak and, even when the car starts after a week or 2, the suspension is at the bottom with warning not to drive. It pumps up quickly and stays up....But can THAT be the source of the leak as well?

This has been such a great and comfortable car, reliable, powerful, and sure-footed, it seems a shame to have to trade it in because this drain cannot be found. And I simply do not trust Mercedes dealerships with cars out of warranty not to run up the bill far beyond the book value of the vehicle...one dealer tried to do that on an old ML500 we had--the estimate was nearly DOUBLE the SUV's book value! Things they priced at thousands (PS pump, rear brake rotors and pads) I did for a few hundred in parts.

Thanks for any help you can give me!

 

Its worth a shot to drive the car to Auto Zone or O'Reilly's and have them courtesy check the car for error codes. While they are limited with their scanners, a bad battery or its peripherals may just give you an error code. Worth a shot. Or find a garage that has a scanning tool.

Yes the MOST can be disconnected. You will need a connector to bypass all modules, or the ones you dont use. Your Nav, Phone, Amp, Teleaid are all inter looped on the MOST system.

 

Thanks. But since none of them are being used, they can all be removed or disconnected. Because now the Nav, Phone, and Amp are all Alpine, and the Teleaid is cancelled because it kept going off in my garage a few years ago and I had them discontinue it. If they are connected to any kind of power, I'd like to end that. BTW, where IS the MOST located?

The battery has been checked in the last several days. It's fine.

 

Read this.

https://us.autologic.com/news/merced...-bus-diagnosis

 

I've already read this article.
I don't want to fix the MOST system or diagnose which components need to be replaced. I want to disable it because ALL the components in it are no longer usable as the Alpine head unit has replaced all of its functions.
But thanks for trying to help.

 

This type of battery drain can always be found if the correct methods and experienced tech are looking for it. The car has lots of control modules and all have to go to sleep before it is actually put into sleep mode. Any faultly control module can be causing the drain. While the MOST system can be the issue, without testing and confirmation it is just a wild *** guess. Find the right shop and get it properly diagnosed. You will save time and money in the long run. Note: these type of issues is what puts these otherwise very nice older high end cars in the salvage yards. To own one of these cars you should either know how to maintain it yourself or have a very capable repair shop that can successfully deal with whatever issue comes up. Not guessing and not throwing parts at it to see it that resolves an issue. The shop you should be looking for and need now is the exception but well worth finding and remaining loyal to.

 

From your lips to....!

I've been hunting and have already had 2 specialty shops, including one which had a certified Mercedes technician, take it. Couldn't find the problem. Each had it for well over a month without being able to find the answer. As for the dealers, I do not trust any of the local Mercedes dealers. Most are now owned by Open Road, as are the local BMW dealers. I've spent hours and hours trying to trace the drain myself with no luck, and, basically, haven't been willing to trust this car to be reliable since before the Pandemic. At some point, as much as I love this car, enough is enough. It's just a car.
At some point the book value of the car, sadly, makes it not worth it. I'm sort of near the end. IF the DCM module fixes the problem of the driver's side window, mirrors, seat adjuster, seat heater/cooler and power door locks, I MAY ask a dealer to spend 2 hours solely on finding the leak, and nothing else. If they can't, we will have to trade it.

 

with my E63, i had to leave my car with my Mercedes Indy 3 separate times for a few days to a week. their 2 employee's combined have something like 45 years of dealership technician experience. with their diagnosis, the first 2 sessions they found nothing. the 3rd session, they were able to catch the MOST network not going to sleep. they said the issue was random and finally identified that central gateway i believe was faulty. ordered a new one from mercedes in germany which took 2 weeks as these are not stocked and need to be coded at the factory. replaced this unit and haven't had any issues since. previously, had intermittent issues over the past 6 months which progressively got worse. the power draw was tiny, and very hard to replicate. sometimes would not appear for months. the only way they were able to was to try many different things over multiple sessions.

 

Tin whiskers, I tell you. Damn lead free solder.

 

Is the Central Gateway the same thing as the heart of the MOST network? I just picked up the car last week and today the battery tester said it had (by eyeball) maybe 1/8th of a full charge--if that much.

 

In a simplistic explanation the Central Gateway (N93) is a hub of multiple computer networks within the car. The car has multiple communication networks working along each other. Individual controllers are part of those networks and are small simple computers that are all connected through the networks by cables. There is constant communication going on while the network is awake. One of the networks in the car is the Audio Gateway (N93/1). The MOST system is part of the Audio Gateway. I hope that helps.

 

That does help. Can I pick your brain further and ask if that N93/1 can be disconnected and where it's located? The entire Audio Gateway is no longer relevant to the car. There's nothing it serves now, AFAIK.

 

The MB systems are completed integrated so you may not be able to simply disconnect it and not have issues resulting. See attacehd for the N93/1 location.

 

Which box is the N93/1? The upper looks like a power amplifier.

I already have issues leading me to want to get rid of the car.

BTW, the Driver DCM module I got off eBay seems to work perfectly but I still don't have power door locks or remote trunk opening.