Battery drain

Tiny
SEYMOURGKS
  • MEMBER
  • 2002 MERCEDES BENZ CLK230
  • 2.3L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 37,000 MILES
From fully charged the battery voltage drops daily by a percentage of a volt. By day five it is down to just below 11 volts but on day six it is flat and reading 2.94 volts.
I have traced the drain to fuse 7 under the bonnet. When this is removed the drain stops.
This fuse controls the wing mirrors, rear windows and internal boot release.
I have unplugged the wing mirrors in the door panels but still have the drain.
I am now stumped as I cannot work out what is draining the battery.
The battery and alternator have been tested with no faults found.
Can you help me please?
Thursday, November 22nd, 2018 AT 10:28 AM

6 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,320 POSTS
Hi and thanks for using 2CarPros.

Have you tried disconnecting the rear windows and the boot to see if the draw stops?

Let me know. Also, let me know if by accident you transposed the numbers for the model. I know of a CLK320 and a SLK230.

Let me know.

Joe
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Thursday, November 22nd, 2018 AT 7:15 PM
Tiny
SEYMOURGKS
  • MEMBER
  • 3 POSTS
It is a CLK 230 Kompressor.
I cannot disconnect the boot electrics as from the boot lid a bundle of wires go down into the boot but just carry on without a plug that I can undo.
I tried pulling the fuses that applied to the boot with fuse 7 still connected but the drain carried on.
I also do not know where to disconnect the rear windows.
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Friday, November 23rd, 2018 AT 1:50 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,320 POSTS
Welcome back:

First, every schematic I found shows power to the trunk, mirrors, and windows on separate circuits. See picture 5 for fuse 7 allocation that I have. Powers back up relay.

The one place I found that the rear windows and boot release come together is in the left front door control module. I attached a portion of the schematic for you to see. However, that is not powered by fuse 7.

Lets try this. Under the dash, remove fuses 22 and 33. These supply power to the rear windows. See picture 2. If the draw stops, then we have to look at the draw coming from the door windows. Also, check pins 3 and 4 at both sides window door control module. Make sure there is no damage where they attach. See pictures 3 and 4. Also, check grounds located in area indicated in schematic.

As far as the fold in mirrors and power to the mirrors, fuse 21 powers the left and 22 powers the right. The fuses are under the left side of the dash. Power is supplied to the left front door control module and the right door module. See pictures 6 and 7.

The last component, the boot, is powered via fuse 21, which is tied with the window switch. See picture 8.

Let me know if any of this makes sense to you. Also, please tell me where you are finding fuse 7.

Thanks,
Joe
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Friday, November 23rd, 2018 AT 3:44 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,014 POSTS
I would bet money that what is listed as the items that fuse powers is not complete. The problem is that Mercedes did not sell the data on the CLK230 to the aftermarket information sites even though they did sell them here. They show the C230 and the SLK230 but not the CLK230. Plus there may also be an issue if this is a UK vehicle as they have a bad habit of building them different than the US spec versions.
However, you are on the correct track, to make it easier to test you can put a test light in the circuit and then just watch it as you unplug the various items. Another thing would be to put an amp meter in place of the fuse. If you have one that can handle the load! Now move/adjust the various items and watch the amp draw. The item or items causing the draw will not increase the draw as much as the circuits that are acting correctly.
If you have a shop that works on them they may be able to get you the correct wiring diagram based on the chassis number.
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Friday, November 23rd, 2018 AT 4:02 PM
Tiny
SEYMOURGKS
  • MEMBER
  • 3 POSTS
The car was built in Holland.
Having spent months trying to resolve this issue and talking to many experts I took drastic action yesterday.
I removed fuse 7 and incorporating an online fuse I fitted a switch on the dash so that when parked this circuit can be turned off.
Previously when fuse 7 was removed the battery stayed good for two months.
Much better than five to six days.
Perhaps one day the fault will become obvious and can then be repaired properly.
Regards,
Graham Seymour
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Saturday, November 24th, 2018 AT 12:39 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,014 POSTS
Well that is one method. Should work. I sent a note to a friend of mine who works on Mercedes in England. He may be able to get me the correct schematic for it. Mercedes does this same thing with many models, they will hold back information to make it so you have to go to a dealer. Sort of ridiculous once the vehicle is out of warranty or is an export but it is what they do.
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Saturday, November 24th, 2018 AT 12:46 AM

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