W203 battery drain : how to investigate

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AirScrew

New Member
Joined
Sep 9, 2013
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3
Car
C220 Cdi Sport
Hi All,

I have a recent and serious drain problem. 13.2 to 11.8 overnight. ie locked and left as normal.
Meaning basic but minimal systems and services should be running in the background.
But something abnormal is draining the battery.
Its a new battery, so disconnected and charging now.

I know can check the 'static' amps drain with a meter.
I posted a week ago, investigating a COMAND related problem.
And an elec auto specialist showed and proved that the COMAND was draining the battery, over 1A infact, in 'locked mode'.

So the COMAND fuse was and is pulled, and at that time the parasitic drain was down below 0.1A.

BUT. I still have a drain on the new battery, as above.
So its not the COMAND.
And something else is kicking in.

So, can any of you good people advise on other likely (ie known) electrical culprits for this scenario.
I dont want to laboriously pull every fuse in turn.
So any suggestions on where to start looking would be very valuable.

Thanks.
J.
 
Comand taking 1 amp still gives you 4 days. Overnight you will drain approx 10Ahrs, that's not overly serious on a 100AHr (or so) battery.

I would want to confirm the 'new' battery is good.

The issue is testing what isn't sleeping, or waking up ,while locked. I'm keen to hear others views on how this could be done.

Testing current draw at fuses can be done by measuring the volt drop at the 2 exposed conductors at each fuse. In truth I challenged the success of this when it was described but tried it myself and had to agree that it seems to be feasible.

This might explain.
 
The cdi has an electrically powered block heater,? It was the culprit on my 203 270cdi. It goes short circuit and flattens the battery. Solution was to disconnect the fatter cable. AFAIK there is no fuse to this unit..
 
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The cdi has an electrically powered block heater,? It was the culprit on my 203 270cdi. It goes short circuit and flattens the battery. Solution was to disconnect the fatter cable. AFAIK there is no fuse to this unit..
Is that the heater designed to give warm air on cold morning starts, below 8 degrees?
I would expect there is a 'stat somewhere to test??
 
No, on the C class it just helps warm the engine coolant, bit like a kettle element. Draws a lot of current.
IIRC there is a setting in the cluster menu somewhere to enable/disable the heater but if it goes short circuit (the usual failure mode) this won't do anything.
The short is usually on the power side (inside the heater) not the thin control wire.
 

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I've been chasing a drain on my w203 also and unfortunately the only real reliable way of narrowing it down is by testing the fuses for a draw.

In my research. Common areas are alarm ( seems to be related to fuse 8 in boot) interior dome lights and light ( fuse 9 in the boot) seats memory ones and heated ones can also be common culprits ( not sure of the number at the top of my head) have heard of the diesel heater also but mines not a diesel so didn't look for it .

Good luck let me know how you get on, ps make sure you follow a procedure for putting the car to sleep and also sometimes if your pulling fuses it sometimes re awakens thing so may have to wait again briefly for it go down
 

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