E-Class (W211) 2003-2009

Battery drain issue on my w211

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Old 03-22-2022, 03:29 PM
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W211 E320CDI 2004r Sedan
Battery drain issue on my w211

Dear all,

I have some robiłem with battery drain in my w211 E320CDI Sedan model from the year of prodction 2004.

I replaced my battery last year. This year I have noticed the issue with additional battery for SBC. The condition of battery was weaker and weekanr so I decided to regenerate the alternator with voltage regulator replacement, and replaced the small battery. Now both of batteries are charging, but after few days of wehicle stop main is going to discharge. I have noticed on the testing device, the charging current is on -3.1Amps level and I have been checking all of the fuses one by one to check which of them has the current flow by voltage drop on them (small value in mV visible if any carruent is flowing by them). I have found some of them, but the take out of them has changed nothing. Maybe the front SAM on the driver side has two of the fuses, where the take out decreased the current by 0.3Amps. Rest of them has changed the current by 0.1A max.

I have read the faults, and the only rear SAM have me some feedback
This 9029 made me worry cause it means the element is broken or the cable has short circuit or breake.

What does it mean?

​​​​​Do I have to replace the rear SAM? I can't find any information about this 9029 fault.

Thank you in advance any advices.
Old 03-22-2022, 05:40 PM
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2004 E500 wagon
A simple thing to check is to unhook all cables to your battery control module. In my case, it was the 2 wire plug going into the module that was the main source of the drain. The other major one I found was the passenger seat control module under the seat, but that was a minor drain as compared to the battery control module.

Last edited by amosfella; 03-22-2022 at 05:42 PM.
Old 03-23-2022, 12:48 AM
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Originally Posted by amosfella
A simple thing to check is to unhook all cables to your battery control module. In my case, it was the 2 wire plug going into the module that was the main source of the drain. The other major one I found was the passenger seat control module under the seat, but that was a minor drain as compared to the battery control module.
Thank you for that quick response 😃

I would like to understand, how did you found it was the 2nd wire plug? Did you found the insulation demage on it?
Old 03-23-2022, 12:52 AM
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Originally Posted by pablo89
Thank you for that quick response 😃

I would like to understand, how did you found it was the 2nd wire plug? Did you found the insulation demage on it?
No. It was that inside the battery control module from that plug. It wasn't from the negative cables from the battery to the frame. Updated the battery control module, and most was well.
Old 03-23-2022, 12:56 AM
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Originally Posted by amosfella
No. It was that inside the battery control module from that plug. It wasn't from the negative cables from the battery to the frame. Updated the battery control module, and most was well.
So you replaced the module and it starts to work? 😐 Holy sh*tty electronics 😁. I will try to check it today.
Old 03-23-2022, 12:29 PM
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That's not BCM

Originally Posted by pablo89
So you replaced the module and it starts to work? 😐 Holy sh*tty electronics 😁. I will try to check it today.
​​​​​​
​​​​​​Next day of the reaserches and new observation. When I measured the current by multimeter it's 0.44Amp. on the diagnostic tool it was 3Amps, but the measurement has to be wrong.
BCM unplugging doesn't change anything. 25Amps fuse on the driver side front SAM, which decreased the measurement yesterday by 0.3Amp doesn't change anything.

What else then de rear SAM can take the current? It's 0.44Amp it's a lot.

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