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Discussion Starter #1
I have been experiencing a weird issue with battery drain. I know my way around the electronics for the most part, but this is pretty strange.

If i were to leave the main relay plugged in, the m5 would have an empty battery by morning. After a jump or recharge of the battery, i can start and run the car. Once I turn the car off and remove the key, there is a faint audible buzz coming from under the intake manifold (assuming icv). I believe this is causing the drain. The usual buzzing in the cabin happens but soon turns off. I know this be be normal (have 525 and had 535i) but the icv would still be on. I traced to the main relay within the DME box; if i unplug, the icv would stop and there is no more drain.

Trying to troubleshoot:
  • Plugging the relay back in, i hear the abs relays click and the buzzing of the icv.
  • Removing fuses results in icv still energized.
  • Removing abs relays results in icv still energized.
  • Disconnecting the DME (not the best way) results in main relay / icv disengaged.
  • There is no issue starting the car in this state.
  • If relay is unplugged with many hrs in between (car sitting for a while), plugging the relay back in results in no main relay / icv energized and no clicking of the abs relays. I can then proceed to stick the key in to start as normal.
Has anyone experienced this? Does anyone know what may cause the main relay to remain excited once the key is removed but, given enough time, will dissipate? I havent had too much time to track down this issue but plan to try pulling all the fuses out with relays and trying again.

This seems like a great community. I just acquired this 1991 M5 which is one of my dream cars. Ive had e28s, e30s, e34s, e60, e70, and boosted several of those plus built the engine controller modded ms. I plan on doing to my first ///M.
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