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'09 CLS 550, '72 MG Midget
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115 Posts
Discussion Starter #1
I got the car in November, 2-1/2 years old with 6k miles on it. So, about a month after I got it I was surprised, but not terribly so, that the battery was dead. I figured must be it was just not real well charged and it had been sitting for two-three days when it happened.

However, it has now happened a total of four or five times. The last two times was within the last week, when it had been started in the AM, driven for 10-15 minutes and then parked for 1-2 hours.

A jump starts it easily.

I'm guessing that something is not properly shutting off, but I may be thinking that because I had a similar problem with my E320 which turned out to be a cabin fan regulator issue.

I drive the car "every" day - once in a while I may not drive it one day, but basically all the time. It's my only vehicle, and I work a regular job...

I mentioned it to the dealer when I was in having a software update and they basically said it was because I don't drive it enough. This was in the winter and they didn't believe me that I drive it every day in Vermont in the winter. That plus it only had like 8k miles on it then and was almost 3 years old apparently gave them that perception. I could MAYBE see it, if it happened after sitting for a couple days, but 1-2 hours?

There are no add-ons except the dealer installed remote starter.

Any ideas of where to look? The nearest dealer is almost 2 hours away so I don't just run there without a good reason.
 

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Premium Member
2004 CLK 240 Coupe
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11,377 Posts
This is definitely a fault - but the real solution can take many hours of fuse pulling and checking ALL fuse paths with an ammeter across the fuse terminals. As you said, some circuits are on all the time, eg ATA, clock, etc.

Do you have a fuse map? There are fuses in the following places:

1) N10/2 Rear SAM & relay box, fuses f1 to f20. (5 used)
2) N10/1 Front SAM & relay box, fuses f43 to f67.
3) F34 Interior fusebox, fuses f21 to f34.

4) F32 Front Prefuse box, fuses f68 to f77. (9 used)
5) F33 Rear Prefuse box, fuses f78 to f91. (10 used)

I would restrict my investigation to the 2 Prefuse boxes, where only 19 fuses need to be checked.

Apart from that - do you have COMAND with satnav? I had a battery drain problem that was 'cured' by not leaving the Navigation CD/DVD in place after switch off. It worked for me!
 

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Premium Member
1985 190E2.6(junked), 1995c220, 2000CLK430(totaled), 2001C240, 2009 CLS
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421 Posts
The 09 doesn't have a nav CD, it's stored on HDD. There is a fuse location diagram ( map, Keyhole is refering to) inside the small compartment( where the fuses are located) by the dash, drivers side it is covered when door is closed, open door pop open little panel between top and bottom of dash.
 

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'09 CLS 550, '72 MG Midget
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115 Posts
Discussion Starter #4
I'm not an electrical engineer, though I do have a basic understanding of electricity...

So what would be the procedure for trying to trace this out? I'm guessing, after the car is shut off, check and see if any of the paths are drawing power? But it's definitely not consistent (although it may be becoming more prevalent), so are you suggesting I run these checks every time I shut it off? Just not sure I get it...

thanks.
 

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Premium Member
2004 CLK 240 Coupe
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11,377 Posts
I'm not an electrical engineer, though I do have a basic understanding of electricity...
That's good enough - especially if you have (and know how to use) a mutimeter. I use a cheap digital type.

Before I would start a battery drain investigation I would make absolutely sure that the battery itself is not faulty. I know it is quite new, but some just fail early in life, and do not hold a charge. The cells can have internal short circuits, and then intermittently fail. So you need a full load check on your existing battery before you go further. If that is OK, you can proceed.

So what would be the procedure for trying to trace this out? I'm guessing, after the car is shut off, check and see if any of the paths are drawing power? But it's definitely not consistent (although it may be becoming more prevalent)
If it fails (when you have the time available to play) switch off the ignition and open up both Prefuse boxes, (front & rear). Be aware that the 12v dc battery supply (known as circuit 30) to the Prefuse boxes is UNSWITCHED, so the battery voltage will be present there with the ignition OFF. So do not short this to the chassis!

Now remove each fuse (one at a time) and prepare to measure any current that would flow via the removed fuse. First, get the probes into the right meter sockets (DC current), and also the right way around, ie. red to circuit 30, then place them onto the fuse sockets and take an initial measurement. If there is the slightest indication of current flow, reduce the meter range gradually, down to the milliamp scale - and re-test the current flow. Make a note of the current measured in all the Prefuse positions. I have noted from the WIS drawings that only 10 fuses are used in Prefuse box F33 (rear), and 7 used in Prefuse box F32 (front) - so this should not take all day.

Let us know your findings...and we will try to tie this up with the associated 'consumer' being protected by the Prefuse. Then we can go forward from there.

Any circuit draining over 20mA must be considered as suspect.
..., so are you suggesting I run these checks every time I shut it off? Just not sure I get it...
No - you will just have to make a stab at the problem when you find time. Checkout the front Prefuse box first, and then later check the rear..:thumbsup:
 

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'09 CLS 550, '72 MG Midget
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115 Posts
Discussion Starter #7
Before I would start a battery drain investigation I would make absolutely sure that the battery itself is not faulty. I know it is quite new, but some just fail early in life, and do not hold a charge. The cells can have internal short circuits, and then intermittently fail. So you need a full load check on your existing battery before you go further. If that is OK, you can proceed.
Well it looks like it may be the battery. An initial test showed it would not hold a charge very well. The guy I took it to (my brother-in-law and ex-business partner who is an Interstate battery dealer) is going to do a high amperage long term charge as he said that often does the trick, and then do an individual cell test. If that doesn't work out we'll replace the battery and hope that takes care of it.

Thanks for the advice!
 

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'09 CLS 550, '72 MG Midget
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115 Posts
Discussion Starter #8
So, one cell was apparently dead. The battery is completely sealed, but once charging he could feel that one was cold. After about an hour of charging it started warming up and after 5 hours it was as hot as the rest. So far it's been fine so I will assume it was the battery, but since it was intermittent early on I guess I won't know for sure until time goes by. Thanks again.
 
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