See also:

Functional readiness of the airbagsystem
When the ignition is switch on, the warning lamp in the instrument cluster lights up briefly and thereby indicates the operational readiness of the entire airbag system and the belt tensioner. ...

Tire inflation pressures X5 xDrive50i with three rows of seats
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Checking the coolant level
1. Do not open the hood until the engine has cooled down. 2. Turn the expansion tank cap counterclockwise slightly to allow any accumulated pressure to escape; then continue turning to open. ...