So, this morning I went out to my garage to start up my C32 after it had been sitting for 2 days. After inserting the key into the ignition, it wouldn't move at all.

The dash, the dome and all the lights were out so, I quickly deduced the underlying problem with my key. I learned that when the battery is stone-dead, the ignition switch won't budge.

Now, what would have caused this sudden battery death? My first thought went to the numerous threads, here, about the cursed seat controller modules that hate our car batteries so much that they are out to kill them all. I got the car jumped and ran it for 45 minutes or so (did some banking via the drive up ATM) and re-parked it in the garage for the big test. The car started up right away. In fact, it started up several hours later also. My guess is that the battery is holding a charge and something is draining the battery. Prime suspect: seat controller.

This is where it gets odd. I ran down to Staples for a bit. When I returned to the car to unlock it, I got the usual pogo bounce (still too cheap to get it fixed) on my drivers door and opened it up. The alarm sounded as I noticed all the other doors did not unlock. Repeated pushes on the lock and unlock buttons did not stop the alarm or unlock the other doors. I finally got one unlock to shut the alarm off. I got in and I tried to unlock the doors with the dash switch. No luck. I had to reach across and lift the pin, manually, to let my son in the car. I suddenly remembered that the last time I was driving the car, I had some clients that had tried to lock my car doors when we were driving through a bad part of town. I ended up using the dash switch then but, I don't know if the back seat passenger force the pin down manually.

Short story, long: Has anyone else heard of a possible battery drain from a faulty/forced door lock switch?

Or, could a low voltage battery cause fault with the door locks?

The chicken or the egg?

 

There are many things that can drain your battery in the car.

I had the same unknown battery drain issue and suspected the seat control module. I unplugged them and the battery kept a charge. I took it in to the dealer, when I had still had warranty of course, and they informed me that there are a couple of other places that could cause the battery drain.

Apparently there is a control module that controls the light that has a tendancy to go bad. I believe that the module is located where the lights and the sun roof control is at. The alarm siren can go bad as well, causing a battery drain.

Apparently my problem had to do with the alarm and not the seat control module. They replaced the alarm siren, claiming that that was the problem.

A few months later, I had the alarm coming on on its own. Some times the siren would sound and other times it would not, but every time my fog lights would flash continuously. Well, I learned that the flashing lights would not stop and that would drain my battery. I cannot even turn on my alarm for fear that I will have my battery drained.

I bought a new alarm siren in hopes of solving the problem, but I have not got around to installing it yet.

I do not think you're battery drain is coming from your door locks, but I would try not arming the alarm and see if that cures the problem. Does your alarm siren always sound when it comes on? It could be the siren/alarm causing the problem?

 

I have recently experienced the exact same issue.
Note: ever since I replaced my Recaro bucket seats with the stockers, I have had this re-occurring battery drain. A real PITA.

Please HELP

 

i believe the car puts out a buzz sound if the battery is low. I remember my car gave off a buzz sound and the door locks wouldn't work and i had the open the car with the metal key right before the battery died.

i don't think its the alarm thats draining the battery. The overhead module is known to drain power as well. I believe topgun32 was experiencing it.

You can pull the power from it, I believe by pulling the #9 fuse in the rear sam. When you pull the fuse your overhead lights won't turn on.

I have a small power drain issue on the overhead as well. It only really effects the battery if i dont drive it for week, so i just leave the fuse in.

 

Low battery plays all sorts of havic on the cars...

My two problems when I had the same symptom when I had the C were due to the seat control module as well as the overhead light module.

I would unplug the 3 and do some more testing. If you are near anyone with a STAR that will tell you failed modules as well.

 

Thanks guys.

I have spent some considerable time sitting in the car (my kids are getting a little creeped out by this), listening for anything . I wanted to confirm that the COMAND fan is shutting down. It appears that this may be the most promising lead. After a half an hour, the fan is still humming away.

Has anyone experienced the COMAND system drain? Is there a simple fix, because I sure don't want to buy a new COMAND unit for this car. If I pull a fuse for the system, will I lose my pre-sets?

Karma is a Bi**ch! I was just bragging on how reliable this car has been for me.

 

simplest way is to cut the constant power wire to command and tap it to the cig lighter. That way it will only turn on and off with the position 2 of the ignition.

 

Star is probably the best way to diagnose a problem. Next would be to use a Amp clamp and start pulling fuses you think that might be affected.

 

I left a charger on the battery overnight (on a 2 amp setting) to make sure I can start it this morning.

I left the window down overnight so I could just stick my head in the car without opening the door. Sure enough, as of this morning, the COMAND fan is still whirring away.

Do you have any DIY instructions for the cut over to the Cig lighter?

 

do you keep your headlighs on auto or manual? when i ran into a dead battery i unplugged both seat modules and still lost my recharge on my battery i ran through a new battery new seat modules and found it was the headlight switch.

but GL with the search.

 

With the COMAND fuse pulled, I am now hearing a whirring sound from the overhead console.

Is it possible that 2 things went out at the same time or would the Seat Controllers cause other malfunctions?

Yikes.

 

Overhead control panel, is a common one, as is the comand.

If a control unit is causing a draw 9 out of 10 times, SDS will be of no help, the best method would be...

Your spec should be no more than 50mA or .050 as read on a multimeter. Also everytime you pull a fuse, you need to wait a few minutes for the CAN to stabilize and go back to sleep.

 

If multiple modules are running, could the CAN be staying "awake" instead of going to sleep?

 

Yes! If the CAN is kept awake, it will drain the battery.

 

Low voltage can wreak havoc on electronics. Your electronics are run by software. Good code (software) will exhibit bizarre, undocumented tendencies if the hardware is bad. ANYTHING other than software is hardware. Looking at once peice of normal wear hardware that the code depends on - how old is the battery? If it’s original equipment, and it’s a day over 4 years, then I would replace it. If it's fairly new, I would have someone perform a load test.

 

Well you have a few options.

1. replace both items.

2. pull the fuses and only plug them in when your going to use them

3. Figure out constant + on both items and hook to ignition only power source.

4. Hook a relay to the + on the rear sam for the command and overhead to the ignition only fuse.

I dont know how much you wanna hack up your oem wires or not.

 

I believe ground is brown and black is +. I'll double check but my car is in the shop at the moment.

https://mbworld.org/forums/c-class-w...hter-help.html

 

Are you (or anyone else) believing that an old battery could be causing software issues that could be causing the CAN to not go to sleep?

I'm assuming I should just go replace the battery today and see if that is the easy fix. If not, I will have just spent $100 I'd need to spend soon enough.

I still would like to really know what is the cause here.

 

I was having the exact same issues!! I ended up running a switch to the power wire going to the command and unplugging the overhead console. There is a DIY to remove the trim around the command on here somewhere and from there it is pretty simply to remove the navigation and find the power wire. I ended up mounting the switch inside the ashtray somewhat out of sight. But after unplugging the overhead console, seat modules, and cutting the power to the Navi it would still kill die overnight! These were the determining factors on trading the car in!

 

try this:

sit inside your car, all windows and doors closed. then lock the car using the remote. wait 30 seconds

 

AAARRRRRRGG!

I was hoping for a nice, easy fix. I replaced the battery this afternoon, thinking that the low voltage was playing havoc with the software and causing my gremlins.

Well, no such luck. After a nice clean swap out, a couple of runs around town to shake any mystery bugs from the system, I still have a COMAND and overhead console drain (at the least) some 45 minutes after parking the car.

Everything else in the car seems to be running normally. I am not showing any malfunctions through the dash. I do not have a code reader though.

 

What we need to figure out is what part is causing the battery drain and see if we can come up with a repair. Is it a capacitor, a short, or some sort of diode. Once we figure out what the problem is it should be a simple repair.

All we need is some on savvy enough to check the parts and see about fixing them. I know it can be done, I just don't know who can do it.

 

The ACCURSED Plan-B


SETP-1:Pull half the fuses.

• Still got the accursed drain? GOTO STEP-2.
• Has the accursed drain has stopped? GOTO STEP-3.

STEP-2: Reinstall the fuses you removed in STEP-1, and pull the fuses you left installed in STEP-1.

• Still got the accursed drain? Either you missed a fuse, or the drain is through a non-fused link. Go to STEP-666-Pay-Somebody-to-fix-this-accursed-drain.
• If the drain stopped, go to STEP-3

STEP-3: Smile, there is light at the end of the tunnel.

• Reinstall half of the fuses you have remaining and GOTO STEP-4.

STEP-4: Has the accused drain returned?

• If not, methodically add fuses until you isolate the one fuse that’s making your life miserable.
• If the drain has returned, pull the last set of fuses you installed and install all of the other fuses. NOW Has the drain returned? If yes, either you’ve done something wrong, or multiple fused links lead to the same drain, or this DAMNED DRAIN HAS GONE SATANIC. Logically, it has to be one or more of the fuses you have installed since STEP-2. Pull the fuses you installed in STEP-3. I recommend patience and logically installing the fuses until the damned drain is isolated.

If there is an obvious logic error, forgive me, this is New Years eve.

 

that's some serious logic right there

step 666

 

You are forgiven. And, a Happy New Year to all of you.

I did do a non-scientific removal of fuses and plugs. I seem to have found the culprit. Remember post #1? Always go with your initial hunch. It turned out to be the passenger seat controller module. It's unplugged for now. I'll attempt the $20 fix at a later date.