HELP - W208 Battery Issue

[Veritas]

Hi I have a 2000 (W) MB CLK230 Convertible (W208). Sometimes, 2-3 times a week (!!), the electric windows and hood don't function unless I do to the boot/trunk and turn the red plastic key attached near the positive terminal on the battery once, wait and then turn it back again. That makes everything fine, but I then have to reset the stereo code each time. Any one know what's going out and how I can stop having to do this? PS: The battery is the correct size and less than six months old. Thanks in advance!

 

[ivan1983]

Can you post a picture, sounds like you might have a battery isolator attached which may have a dodgy connection

 

[markjay]

Firstly, a new battery can still fail.

Then, there may be an issue with a rogue electric consumer that drains the battery overnight.

And, there could be an issue with the battery charging system - poly belt, alternator or voltage regulator etc. Is the car driven often?

And last, there could be a loose or corroded battery connection or earth connection.

I would start by getting the battery tested with a load tester (auto electricians have them), preferably at the same place where you bought the new battery and have it investigated under warranty.

 

[andy27168]

Hi
As Ivan said that red plastic key isolator does not sound like it should be there, and was probably installed to deal with the issue you are having now.
The issue you are having sounds like a possible control unit (roof?) or SAM fault, which effectively is the guts of the front fuse box.
What else doesn't work? Horn indicators lights, heated screen etc.
If it is limited to the windows and roof then I would be looking at the roof ECU, if there are other issues eg horn, hazards, indicators, heated rear screen, seats, lights etc at the same time then I suspect the SAM unit.
We are guessing at the minute really needs to see if there are any fault codes, though replacing the SAM with a second hand one from Ebay would probably be cheaper than a diagnostic (if a good one can be found).

 

[andy27168]

Hi
Quick look on ebay, brings up a few

mercedes clk convertible sam unit for sale | eBay

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[Bert_W164]

It could well be an issue with a SAM, unfortunately you and I are a great distance apart otherwise I would have checked your car for codes. Hopefully someone with a scanner next to you may visit this thread.

its worth ruling out the obvious things first, the list @markjay has written, if you have a multimeter you can check the voltage of the charge system while engine is off and on, and with load to rule out alternator, battery, voltage regulator, bad connections, if all that checks out then really you need to check the control units to see what's really happening.