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Thank you gOrsq, I have been studying the schematic since yesterday and I can see K75 is a double through relay, where the positive signal for the coil comes from 30a and to activate a ground contact should come from pin 10 of the BCM to pin 1 on the K75. Will test all that today to see the results!
K75 does not control the consumers, just the front cigar lighter and the rear power outlet in the trunk. I'm really not sure what MB was trying to do with the dual pole relay. One pole is fed by F11, the other by F61. However, only one output is used. On the early cars, the F61 feed is used to power both the lighter and the outlet. On later cars, the F11 feed powers both. At the very end of production, they went to a single pole relay with power provided by F11. In any case, it is a normally closed relay, so without the BCM, you will still have power to both.
Consumer functions are controlled by CAN B. Non-critical functions require periodic messages from the BCM to function. Without the BCM CAN messages, these consumers will not function. In order for them to work, you ideally would have a system that monitors voltages and sends the appropriate messages. If you want to ignore voltages and just turn on all consumers, you just need a device to inject continuous CAN messages onto the CAN B network. On the Facebook BNS fire group page, there are instructions on how to modify a CAN filter to do this job.
Sorry I stand corrected. I misread the drawing. I had been reading the drawings for the W211 and got it into my head that the consumers were switched in a similar way.
Mike, You are right, K75 does not control consumers. This morning I tested the unit by interrupting and grounding one of the coil poles (Pole 1) and the radio didn't come on, not the roof. By discarding possible feeds, this only leaves the CAN B connections 6 and 7. I need to find how to implement that CAN Filter..! I will look at the Facebook BNS fire group page..! I have measured the voltage on these terminals and are 12 VDC, but wonder if it is a modulated pulse!
gOrsq, before I saw Mike's message, I was going to let you know about my test...indicating the K75 is out of the equation..! Perhaps need to take a good look at the W211 system to see how the consumers are connected in that model!
I am sure that with the help of you guys at one point in time all this "electronic puzzle" will be decoded. This research will bring hopes to all other owners who at one point in time will face the same BCM dilemma.>! I will keep on digging and testing as time permits...my mission is completely bypass the BCM..! I already have the DC to DC charger charging the starter battery when the car is running..!
Gentlemen, CAN messages are more complicated that I really imagined....After educating myself on CAN bus technology, I have learned that CAN messages are very similar to a software instruction similar to those used in the Config files of a computer. The Message has an identifier, which establish the address, a data field which is the main message, and the CRC field which acts as a spell checker to validate the message. So, to really customize a CAN message it is necessary to have the right tools which extract the data and then is analyzed in a PC. One of these devices is a Autopi Mini which plugs into the OBD2 and extracts the data. This is something for a Computer guru! Any around?
The USB-CAN-B in my message above is another tool which in a way would need the OBD2 adapter..!
Below is a sample of CAN messages.!
Tom in your BCM fix you add a 30 fuse. Is that better than a 25 fuse like on the fuse kit that “Mercedes top seals” adds. I’m just trying to understand. Thanks
2000 R170 SLK 320 manual, 2018 E200 E Class Estate, 2016 GLA 250, 1996 R129 320, 2003 R230 500.
If you mean me, I didn't have a BCM repaired there but the EIS, but having found someone who can fix these things when everyone else says they can't I thought I would pass on the word!
TTFN
06-29-2024, 11:08 AM
