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I have tried to find similar topic through the forum, but I didnt.
I am facing a problem with my w211 e270. I am facing battery discharging problem and I still can't found the problem root.
However, couple of days before, i took off my rear battery's negative clamp for night time, because I needed to make sure that I could start my car in the morning (because of battery discharge). When I came in the morning and put on the negative battery clamp back and sit in the car, I have "BRAKE DEFFECTIVE" red sign on my dashboard and it's beeping a lot.
Nothing helps so far and it keeps showing the message and making this annoying sound.
I know that both batteries are good, and that my SBC already changed into the good one. Nothing wrong with brake system either. it has to be something else.
the question: what could caused this failure with red message after battery disconnection? have anyone faced similar sitaution and where to look for the problem?
You need to hunt down your current leak first, batteries are not good if drained... have you checked what voltages are now? could also be an isolator relay issue connected to current draw but here some info about current draw only...
from WIS:
An average value of 60 mA should not be exceeded (standard value < 40 mA).
Cause of fault 1:If the readings are between 1.2 and 2.5 A, a control unit is usually responsible for keeping the "Bus" awake.
In the event of readings between 80 and 180 mA, a control unit usually does not switch off, thereby resulting in an increased quiescent current consumption.
Separate the control units from the rear SAM
control unit with fuse and relay module
(N10/2) one after another. After each
measurement, reinsert individual fuse and
continue with next
In the event of cause of fault 1:
Wait 6 minutes in each case, repeat
measurement until "bus" goes to sleep.
When the fuse for the component causing
the problem is removed, the no-load current decreases immediately.
Remove fuses singly one after another and
localize defective control unit
In the event of cause of fault 2
Disconnect control units from the CAN voltage distributers
As an alternative to the fuses, it is also
possible to disconnect the control units from the bus.
AR54.10-P-1030-08T
see
Wiring diagram for interior CAN bus PE00.19-P-2300DA
(X30/4)
Wiring diagram for interior CAN bus PE00.19-P-2300DB
(X30/7)
Wiring diagram for interior CAN bus PE00.19-P-2300DC
(X30/6)
Then faulty regulator of alternator may drain battery too!
Well, I have tried to find where the leak appears. When my car is at sleep mode it shows value of ~130 - 140 mA, which is a lot more than 40mA as the best case.
By taking each fuse from all 3 places (hood, panel side, boot) nothing changes.
It does make a change when I take off additional cabel from positive terminal (*** in the picture), then the value becomes good.
At first it seemed that it is Battery control unit fault. I took it to the electronics fixer and he noticed that one of capacitors do not keep the load. Therefore he changed capacitor into the good one and now the control unit should be okay. But unfortunatelly it gave no change regarding battery draining. So it needs to find out what other modules, units are connected through this cabel.
Alternator works good. No drain appears concerning alternator - checked. Also when I yield a load to alternator it evens the charging voltage.
But then still there no answer about "BRAKE deffective" message which appeared because of battery disconnection for ~12 hours.
Have you tried to disconnect can control units like described in those WIS document I referred? Voltage regulator fault you can test by disconnecting alternator and measure drain...
If system has drained also front battery, it will give you an error message. On the other hand grounding problem may cause the same, check connectors of the SBC, ground lead between chassis and engine block, all battery leads, front pre-fuse box (passenger footwell).
Edit: if isolator relay of aux battery is not working, current drain may have drawn aux battery voltage down, what are voltages of you batteries now?
I checked the alternator in the way you mentioned, but I just wrote that I made some extra test of alternator operating quality.
Well I guess I will need to check voltage distributors. Also, I forgot to mention that before "brake defective" messaged I always had message : Malfunction electrical consumers off" but the all the convenient equipment works fine. I guessthis message is very associated with the battery drain.
The auxiliary battery is new and the fuse has a circuit, so I guess it is okay too. I tested also the K57/2 relay with diagnostic computer and it works (connecting and closing the circuit). This battery drain is bothering me for already 6 months, therefore I had to change batteries into new ones.. Car was inspected several times by MB specialists, but nothing found so far.
EDIT: I will try with can control units, since all other ways has been tried. But I am afraid it will help only to find the leak, but not the asnwer to the brake fault message
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