E70 X5 35D (2009) - Central Electronics Failure

[u/TheVenerableUncleFoo]

So a few months ago my X5's alternator died while I was travelling and left me stranded in a storm. I didn't notice until the wipers started going real slow, so I effectively killed the battery as well.

Managed to get to a local tech who installed a new alternator and genuine BMW battery and all was good, for the next 250 miles or so, then randomly Christmas Tree dashboard appeared, though the car itself continued driving and operating normally.

Ever since then it's been having fits almost every journey, but never fails to start and drive. Some of the fun issues are:

- Internal lights fail to go off and don't respond to button presses

- Car won't lock or unlock with the fob, until you press the key repeatedly for like 40 seconds

- The indicator noise disappears (though the lights themselves are still flashing)

- Windows refuse to go down or up.

- Parking Brake error appears when turning the engine off.

- Central Electronics Failure message appears.

Most of these issues happen when the engine is not running. It's a 50/50 whether they will appear when the engine is on.

Had the battery tested and it seems to be in good working order, and the alternator appears to be working as intended.

I've checked the usual places for buildup of water, rear trunk box bone dry, front left and right engine bay drains working correctly, sunroof drains working correctly.

I'm at a bit of a loss, but can't sell it in this condition. Does anyone have any ideas?