Is everybody beside terminator missing the fact that the 5th button is for the passenger seat occupancy mat sensor?
Do you not have it in yours?
What am I missing? I thought your question was what is the 5th button..and not related to the ultrasonic sensor which has it's own space on that console.

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2006 X5 4.8is LeMans Blue / creambeige interior
Prod.date: 2006-06-21