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Discussion Starter #1
I would welcome some information on this feature if anyone could help.
1994 UK C class 250D.
Battery goes flat after a week.
Current drawn from the battery with everything switched off is 160 Ma, which
is not inconsiderable
after a few days.
Tried removing fuses to locate which part of the car is drawing this
current.
Finally arrived at the rear fusebox, close to the battery, withdrawing fuse
9 (7.5 amp)
reduces the current drawn to around 10Ma which is what I would expect, clock
, radio memory etc.
In the cover of this rear fusebox fuse 9 is designated as the fuse for the
Convenience Feature Control Unit.
No amount of Googling seems to be able to find out what this unit does,
permanently removing the fuse
doesn't seem to remove any of the cars features.
If anyone has come across this Convenience Feature Control Unit before I
would very much welcome their input.
Many Thanks
Regards
Dave
 

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1994 C280
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5 Posts
I have the same problem as you, so I pull up this thread again!

My "Control unit relay convenience feature"-relay is pulling about 123 mA!
IR-system is pulling 4 mA, antenna 5 mA, radio 1 mA, and then I have about 50 mA which I could not find the source to. Total 181 mA is draining when everything should be pretty off.

My main problem is that I have to low charging voltage for the Norwegian winter. After a day or to with below -10 C I have to charge the batteri. Common problem with this model in Norway.

I have 14,5 V at the alternator, but only 13,7 V at the battery. And with only 13,7 V to charge, the battery will of course go dead! And given some time destroyed! All voltages is stable at different loads and different rpm's.

So what do I do? I am right now installing a new fat cable in parallell from the alternator to the batteri. Then I expect to lose only 0.1 V in the cable giving the batteri ca 14,4 V which shuold be OK during the Norwegian winter.

But, what is the "Control unit relay convenience feature"-relay doing? It is engaged when the fuse is in, and pulls ca 123mA. Is this normal?

Regards,
Morten W
Norway
 

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1995 C220 elegance auto.
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146 Posts
Found it!! This controlunit is mounted in the boot/trunk behind the battery and allows you to close all the windows and sunroof by holding the IR or key in the lock position for about 5 seconds when locking the car,I think it also has other functions depending on the spec. of the car. If it is constantly draining current there is possibly a relay stuck shut.
Hope this helps, George.
 

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1994 C280
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A-ha!
And maybe this is why I am not able to close the windows and sunroof with the IR-key?
I'm out checking the relay...

Thanks you very much! You are genius!

Regards,
Morten W.
 

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1994 C280
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Hello again!
Well, the relay is always engaged in mine car to. Then there is either something wrong with the relay or with something controlling the relay. And here stopps my knowledge...
Then Dave and I have the same problem.
Any inputs?
 

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1995 C220 elegance auto.
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146 Posts
At least you've found the reason for your power drain and can pull the fuse to allow you to use the car. I think I used this locking feature about twice in the three years I have owned my C220 so i don't suppose you'll miss it in the meantime while you investigate further.
George.
 
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