What I would do is I would try to sort of let iDrive reboot itself by turning everything off, locking, maybe even push in the fob and pull it out, etc and come back again.

One time, my iDrive would just turn off after i turn the engine off (it's supposed to keep playing music, and electronics should stay on until you get out and lock the doors) I unplugged my iPod, I turned everything off and locked it- the next day, iDrive came back to normal.

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2007 4.8i Space Grey, 20", black nevada interior
All options with no 3rd row, rear entertainment,
handling pkg.