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Ian Smith

Electrical issue with drivers door master switch

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Hi, i hope you all will be able to help me, i have a 2000 e39 m5 which is an amazing car except for one annoying issue. On the drivers door there is the master switch which enables the driver to operate all the windows, adjust the mirrors and fold the mirrors, the problem i have is that mine isn't working as it should. So basically i can operate the drivers door window only not the other 3, i can only adjust the drivers door mirror not passenger one, i can fold the drivers door mirror not the passenger one and i cannot lock the drivers door with the remote only manually with the key. I have replaced the wiring loom within the door with a brand new loom from BMW, i have replaced the switch assembly with one from a breakers and i have replaced the lock actuator with one from a breakers but it is still not working correctly. Can anyone help point me in the right direction please?  

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I had similar symptoms. I also found that the seat memory switch would not make the seats adjust. I eventually found the cause to be a break in the P-bus between the driver's door module and the GM. The P-bus is a 0.35 mm2 (~22 AWG) wire, blue with red stripe.


In my case the wire break was inside the tubular boot/snorkel between the door and A-post. However, I found signs of old corrosion in the A-post plug and a kludge of a repair on the P-bus which probably stressed the wire causing it to flex and break as the door was opened and closed over time. I've never seen reports of failure in this joint in the 7 years I've been following with E39 forums; it's an unusual problem. Unlike wire breaks in the trunk (boot, to you) lid wiring in the boot/snorkel.


As a first step, I'd check continuity on the P-bus between the door module and the GM since those two ends are the easiest to get access. Assuming a failure is found, have a look at the A-post connector. 


BTW, the standard practice recommendation would be to remove the door for access to the A-post connector. If you have patience and correct tools, you can separate this connector with the door wide open. By correct tools I mean L-shaped keys or short 1/4 drive bits to remove the two bolts holding the connector to the A-post. I vaguely recall Torx but sorry I'm not sure of that; it may be socket head hex (allen). Definitely not phillips or conventional hex head. Once the connector is free, you'll find a typical lever lock to separate the two halves on the back, car side, of the connector.




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