For several months I have been having some bizarre electrical problems in my w210. It actually started several years ago with one of my power windows (i don't remember which one) quit working. Shortly after that window quit working all the others would quit working. After hours of diagnostics a indy mechanic told me that my rear passenger window motor was shorting out all the rest. He disconnected the motor and I haven't had a problem since. Most recently my front passenger window quit working, and shortly after it stops my other windows will quit working as well. I can disconnect my battery for an extended time and it seems to reset the problem, but it always comes back. Most recently I was attempting to unlock my car with the key fob and it would not unlock so I had to use the metal key. As soon as I opened the door the alarm went off, the hazard lights were flashing, and the tow light was on. I started the engine but the alarm would not shut off and my hazards continued to flash and none of my power windows would work. I had to drive home from the grocery store with all this chaos going on. I disconnected the battery overnight, and this morning I reconnected the battery and immediately the alarm started going off again? Ideas please?

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2006 E320CDI- current dd
1999 E300TD - retired
Wilmington, NC USA

https://www.youtube.com/watch?v=zChaQHHaeJU

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CENSORED due to not family friendly words

Your mechanic was mostly right: these things are all clients on a network called the CANBUS. Problems on one cause communication issues with the rest. Google Canbus if you want to know more - there's a pdf that explains it better.

But, to troubleshoot, you can disconnect the connections one at a time, do a battery reset, and see if the problem recurs. They all connect here: Where is the CAN bus connector X30 on a W210?

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Prost!

This sounds like a Door Control Module (DCM) problem. The best way to diagnose the problem would be to run a quick test using SDS. The faulty DCM probably won't show up on the quick test. FWIW, the mechanic disconnected the DCM, not the window motor. That's why the problem disappeared.