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Old 11-11-2010, 10:30 PM   #1
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w203 battery drain - as usual...

Hi all,

So I've got the common battery drain problem. Had a read of all the posts related to this issue and decided to find out where mine is coming from.

Connected the car up to a multimeter and had a 1amp drain.
Disconnected fuses one by one and found that:

Disconnected fuse 64 and current draw dropped to 0.15amp
same with fuse 45
and same again with fuse 47.

So I need help on trying to identify what these fuses connect to and how to identify the problem areas?!

Thanks for the help chaps.
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Old 11-11-2010, 10:41 PM   #2
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I actually have this too.. Could you please point to some reading material? how do you connect the meter for instance?

I had my drain diagnosed in MB with star machine few years ago. They said that this is happening somewhere in the central can with all the wires. So the finding the actual problem and fixing it might take unknown number of hours..

Considering 100 + VAT per hour I thought we are talking 1000-2000 of money...

Are you saying it can be done DIY simply by getting through each electric loop trying to isolate one particular wire?


Found some links here. battery keeps going flat

Last edited by maxima; 11-11-2010 at 10:58 PM.
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Old 12-11-2010, 06:51 AM   #3
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Quote:
Originally Posted by darthmal View Post
Hi all,

So I've got the common battery drain problem. Had a read of all the posts related to this issue and decided to find out where mine is coming from.

Connected the car up to a multimeter and had a 1amp drain.
Disconnected fuses one by one and found that:

Disconnected fuse 64 and current draw dropped to 0.15amp
same with fuse 45
and same again with fuse 47.

So I need help on trying to identify what these fuses connect to and how to identify the problem areas?!

Thanks for the help chaps.
Did you wait long enough after switching ignition off and before reading the current drain figures, allowing the car to go to full sleep first?

Fuse #45 should be for the SRS system, fuse #47 would be for the cigarette lighter and glove compartment illumination, #64 is for the radio/Comand.
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Old 12-11-2010, 07:05 AM   #4
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If you have memory seats it could be those. My issues were diagnosed as COMAND by one garage but correctly as seat controller by MB.

COMAND drain can be resolved by a software upgrade - if applicable.

If you search my thread "COMAND causing battery drain" you will see lots of good answers.
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Old 12-11-2010, 07:08 AM   #5
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I had the same problem ..after all the the tests it was resolved by fitting a new battery.

Job Done !!!
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Old 12-11-2010, 02:26 PM   #6
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Quote:
Originally Posted by maxima View Post
I actually have this too.. Could you please point to some reading material? how do you connect the meter for instance?

I had my drain diagnosed in MB with star machine few years ago. They said that this is happening somewhere in the central can with all the wires. So the finding the actual problem and fixing it might take unknown number of hours..

Considering 100 + VAT per hour I thought we are talking 1000-2000 of money...

Are you saying it can be done DIY simply by getting through each electric loop trying to isolate one particular wire?


Found some links here. battery keeps going flat
In order to measure quiescent current you need to disconnect the negative battery terminal. Select multimeter DC amps high range 0-20 and connect multimeter leads one to negative battery terminal and the other to the disconnected terminal clamp. Now decrease multimeter DC amps range until you get a reading, should be around 30 to 40mA on the 0-200mA range. If you get a negative reading reverse the multimeter leads.

Take care when disconnecting/reconnecting battery, you can damage the rear sam also you may need to reset windows and traction control afterwards.

My guess is that if you have excessive battery drain the culprit will turn out to be a memory seat control unit (PM me for a workaround) or Comand 2 (try firmware upgrade).
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Old 12-11-2010, 10:28 PM   #7
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Thank you Stan. Mine has neither command nor memory seats.

I read about the most common issues but doesnt seem to fit.

I think I have something more plane. I think somehow rain is getting inside some cavity with the wiring as it seems to be worse in wet weather.

Yes I recently had a lot of fun with disconnecting battery (lost information on service and had my keyfob rejected) so I am not risking on doing it again to measure current...

Not now at least But thanks for the offer.
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Old 15-11-2010, 12:25 AM   #8
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Thanks for the help guys.

Well I waited about half hour, not sure if that was long enough?

As far as Im aware, COMAND is the double din unit? I've just got a standard cd/radio unit in mine so Im assuming it cant be the comand?

Also, the memory seats, Ive got electriconically adjustable seats (except the moving forward/back thing) I doubt these are memory seats?

Ive just had a new mattery fitted so I hope thats not the problem!!

I was thinking, is there some sorta link between the three 3 fuses? as Im assuming theres a common system that is disabled when removing those 3 fuses as the drop in current drain is the same each time?
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Old 15-11-2010, 08:26 PM   #9
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Other culprits known to cause excessive battery drain are the boot light (not going off-faulty switch) and the Overhead Control Panel (interior lights control/sunroof/temp sensor).
Remember always to remove key from ignition when connecting/disconnecting battery terminals and/or ammeter to measure current drain.

darthmal, did you take necessary precautions when connecting new battery. If not I would check your rear SAM for correct operation.
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Old 15-11-2010, 08:27 PM   #10
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hi
the link is after switch off the system keeps some circuits alive up to a few minutes.the seat controller shuts this down and when faulty it keeps everything alive. 1 amp hour over 3 days easy to kill your battery.this is the most common fault and normally is the drivers seat. another comon battery drain is diodes in alternator shorting and keeps field coils alive untill batery dead.

good luck

Abby
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Old 15-11-2010, 10:03 PM   #11
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The seats you describe are called 'part-electric seats' and are not memory seats.
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Old 20-02-2011, 12:29 PM   #12
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Just thought Id update on the solution I found that worked.

I removed fuse #64 and the battery has stopped going flat. Didnt drive it for 2 weeks and came back to hear it fire up first time. Before, the battery would be dead within 2 days.

So far theres been no ill effects of removing that fuse. I dont have Comand fitted, just have a radio and it still works fine.
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Old 20-02-2011, 03:02 PM   #13
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There must be something else connected to the fuse 64 circuit, otherwise it wouldn't be drawing current.
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Old 20-02-2011, 04:22 PM   #14
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Thanks guys, my battery drains too, thinking of a star diagnosis as I'm unsure I could DIY this. Anyone experience same with E220 cabrio 124?
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Old 14-04-2011, 02:42 PM   #15
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I also have a problem with my W203 battery going flat after a few days. I do not have the command unit so I will try removing fuse 64 to see if this helps.
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