WARNING: This page is about a different car, the 2013 BMW 550i GT, 2012 BMW 550i GT, 2011 BMW 550i GT, and 2010 BMW 550i GT. However, it is still accessible from the selected car via links, so may be relevant.
Press in lock (1) before installing quick-release coupling.
Push on hose.
Quick-release couplings must clearly snap audibly into place.