Battery Drain with odd symptoms SLK 200 1.8 2006

Mike Vybiral

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SLK200/2006/1.8
The alternator was 'leaking' and has been replaced. This reduced the drain to 1.7A when locked. Curiously, when unlocked, after 30s, the drain drops to 0.5A. But, after 20 minutes, it increases to 1.7A. The battery is good and even after 24 hours will just about start the car.
The temporary drop to 0.5A is a mystery. Just wondered if it is sufficient to give anybody a clue as to where to look next?
Thanks,
Mike
 

Uncle Benz

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Mainly Mercedes
Does your alarm siren work and sound normal?
 
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Mike Vybiral

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Yes, siren is annoyingly loud and seems to operate normally.
Thanks,
Mike
 

peternutkins

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c220 cdi estate 2001
What is probably happening is that the ECU is shutting down but something is starting it up again. I had this problem on a C5 some years ago and it turned out to be the radio! Someone had replaced it with an aftermarket one which had the same connectors so you could just plug it in but wasn't compatible with the electronics on the car.

I'm not suggesting that is your problem but it would indicate that something is being switched on that shouldn't be. The way to trace it would be to remove the fuses one at a time until the current drops, it shouldn't be more than about 100 - 200 ma. You should then be able to find out what the fuse does and check it.

Peter
 
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Mike Vybiral

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Many thanks for your advice.
Mike

What is probably happening is that the ECU is shutting down but something is starting it up again. I had this problem on a C5 some years ago and it turned out to be the radio! Someone had replaced it with an aftermarket one which had the same connectors so you could just plug it in but wasn't compatible with the electronics on the car.

I'm not suggesting that is your problem but it would indicate that something is being switched on that shouldn't be. The way to trace it would be to remove the fuses one at a time until the current drops, it shouldn't be more than about 100 - 200 ma. You should then be able to find out what the fuse does and check it.

Peter
or
 
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Mike Vybiral

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SLK200/2006/1.8
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Thanks for all your comments.
Latest is that I found the radio fuse in the front fuse box dropped the battery drain by 0.3A.
None of the fuses in the cabin/dash fuse box made any difference.
The rear fuse box is yet to come. I know where it is but have yet to work out how to get to it. There's quite a fancy retractable rain cover. I can't imagine I need to remove that. I reckon there are some plastic trim retaining fixing somewhere. That's tomorrow!
Thanks again.
Mike
 
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Mike Vybiral

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Continuing my pursuit of the battery drain, today I disconnected one of the three cables attached to the +ve terminal of the battery. See attached pic. This dropped the drain a further 1A. (I presume the other connections are to the starter motor solenoid and pre-fuse box ).
Question: Where does this cable go?
My guess is it goes to the dashboard fuse panel. My reasoning is that on RHD models the dashboard fuse panel is just the other side of the bulkhead from the battery, so why bother to run a cable from the battery over to the 'pre-fuse' box on the RH side of the car and then back to dashboard fuse panel? To corroborate this view, this RHD SLK has a connection missing on the pre-fuse box. Missing that is compared to all the diagrams I've seen. (See pic).
If you have any experience of this issue, please confirm my view ... or put me right!
Many thanks,
Mike
20190122_163234.jpg 20190122_163313.jpg
 


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