krsone579

Hey guys....

So I have a bad battery drain, typically overnight. Fuses #3, 6, 9, 29, 31, 33, 34, 41, and 42 are drawing power after the car attempts to sleep! 33 and 34 I am not too worried about as they seem to be the power seat control module, so I assume I can rewire them to ACC on only or something similar that can be found on here.

3 - navigation/TPMS/
6 - AGW
9 - Overhead control panel control unit
29 - Steering column module/ EIS control unit
31 - Upper control panel control unit
41 - Central Gateway Control Unit
42 - ME-SFI/ Driver side SAM control unit

They also seem to cycle on and off. #29 and #41 are the highest draw at .11

So I am thinking it has to do with the radio/AGW/Headunit perhaps being bad?

Any way to definitively test units one by one or does anyone have any insight or ideas?

Thanks in advance!

Plutoe

Faulty SAM

krsone579

Thanks for the reply! Is there only one SAM? Where at? How sure are you or is this just commonly what causes it? Just wondering before I attack and replace things.

Can I unplug the SAM and test for draw etc?

krsone579

So I have done this draw test before and still cannot get the draws to go away. So I did it again slowly last night and still the same result which im not understanding. Pulling every fuse one by one in the trunk, drivers side dash, and under the hood and the only ones that made a change were...

Fuses #
21
22
29
33
34
41
55
64

All of these affected the draw by around .1AMP each. Originally car bounces between .40 - 1.55 Amp draw. With all of these fuses pulled it was still bouncing between .13 - .76

What is causing the readings to continuously bounce up and down and why didnt any single fuse cause that to stop or cause a major drop??

Thanks in advance.

bbirdwell

Current draw of 1.2 to 2.5 amps is caused by a digital module not allowing the CANBUS to go to sleep; all modules stay awake. Current draw of 80 mA to 1.2 amps is caused by a faulty module failing to shut off. Sleep mode should be ~40mA current. You have a bad module. Like Plutoe stated, sounds like a bad SAM, otherwise pulling the fuse would have disconnected the bad module.

For the first, pull fuses/relays one at a time and then reinsert. For the second, start pulling fuses until it quits. Multimeter with positive to battery positive, negative to BCM chassis ground, current capacity ~20A as the windows can pull that much current if activated and blow your multimeter. Put it on a diagnostic system and let the diagnostic system tell you what is wrong.

krsone579

So it took removing (unbolting) F78, F79, and F81 on F33 block to get the drain down to .04-.05 amps. It’s fluctuating. Is this just due to inaccuracies in my cheap meter or the car natural fluctuations or is this some underlying issue that’s waking other things up and multiplying the issue? Otherwise it looks like drivers and rear SAM and interior fuse box (F34) are all affected!?

bbirdwell

Caveat: I'm using fuse diagrams for the 2006 model year W211. Unknown if the 2008 model year used different assignments.

I don't know if you are using this process but here it is:
-Trunk lid open,switch wedged closed position (trunk light off).
-Multimeter tied between positive post and BCM ground point on chassis.
-Key out of ignition. If keyless-go, key shielded and/or outside transmission range to the car.
-Monitor multimeter; waiting maximum of six minutes the bus should go to sleep although it can take as long as 30 minutes for minimum activity.

I find it unlikely both SAMs failed plus a module hanging off of the interior fuse block. What is interesting is you pulled the fuse to the front SAM (F78) and when you pulled the power to the interior fuse block F34, you also killed another source of power to the front SAM (F42 in the interior fuse block). The front SAM is powered by both F78 and F81. The rear SAM is powered by F79.

Put it on a diagnostic system and see what it pulls out of error memory.

krsone579

Any good scanners or systems or recommendations for scanning it at home, since a paid diagnoses at a shop will have to be done a multiple of times and Id prefer to have a way to do it myself if possible. Whats a good cost effective model or unit etc or what have people had success with?

krsone579

I was using that process although with my multimeter tied in series between the negative post and negative cable itself. I am wondering if this issue is causing the rear door to be dead or if that is causing the drain or if its unrelated. Previous owner attributed the door not working to some sort of water related mishap ( ) but didnt have much information. Of course that could lead to anything....

krsone579

I assume this came off due to moving the cables/battery etc and wore off..... What is it exactly for? Also I have the connector apart but cannot seem to get the pins out completely to re-solder the wires on.

konigstiger

I understand wiring broke off connector was any damage caused to receptacle permanently attached to battery cable. If so, https://www.ebay.com/p/MERCEDES-211-...OEM/1228580436

krsone579

Thank you... just the wires broke off and cannot seem to be reattached. Can I just wire them into the clamp or terminal connection since its all ground? Or can I buy just the connector part and not the whole cable too? Thanks again

LexBrett2

Hey Guys,
Thanks for this thread it is really useful.. I just replaced my battery and have had some unexpected low voltage issues. It sounds like I just need to check that these wires connected to the negative battery terminal are firmly connected?

krsone579

I found this under the passenger footwell area. I removed it and measured drain... 40-60 mA, within spec but still fluctuating a bit.... I am hoping this may be the issue instead of just interrupting the power supply to the problematic part, by removing this board. Attempted to clean up the board but it looked to be a goner... havent tested drain yet with it back in there cleaned up either, I will later tonight. Inexpensive replacement part comes in later this week, hopefully no programming required... Any thoughts?

krsone579

To close up the issue.... that Body control module board with corrosion was the issue. I ordered a replacement off of ebay used for just $30 and everything is back to normal. No more drain outside of spec. Very pleased. Now the only issue is the rear drivers side door seems to have no power. I tried checking the harness but cant seem to see much....any thoughts?