WARNING: This page is about a different car, the 2005 BMW 745i, 2004 BMW 745i, 2003 BMW 745i, and 2002 BMW 745i. However, it is still accessible from the selected car via links, so may be relevant.
Open cap on coolant expansion tank.
Fit special tool 17 0 002/17 0 005.
Fig 1: Identifying Pressure Gauge
Courtesy of BMW OF NORTH AMERICA, INC.
Build up gauge pressure of 1.5 bar, wait approx. 2 minutes.
Cooling system is leak-free if pressure drop is max. 0.1 bar.