Okay, so update to my problem.

Twice now I have had to use the three-button iDrive reset on the car (eject-eject-mute) to get iDrive to start working again. From my perspective, it seems like it does this every time the car is started. Seems to me like the problem goes deeper than simply a problem with the Sirius interface, and maybe deeper down into iDrive itself. Anyone have similar experiences with this? Should I still deal with the tedium of trying to reprogram my Sirius, or is there something else that I should try to troubleshoot?

And just to verify that the problem wasn't a low charge/low voltage state with the battery, I had the battery on a battery tender after identifying that the battery charge was low, when I returned from my trip. The battery itself has been installed in the car for less than 18 months, and I replaced my alternator at the same time. Battery terminals and the power and grounding cables are clean and corrosion-free.

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2007 BMW X5 4.8i - Sport Package, Wife's Car

2001 BMW 325i - My Car.

2005 Ford Excursion Limited 4x4, 6.0 Powerstroke Diesel. My first "grown up" car.