1) Quick-connect coupling with ID marking: Assembly
WARNING: This page is about a different car, the 2012 BMW 328i, 2011 BMW 328i, 2010 BMW 328i, and 2009 BMW 328i. However, it is still accessible from the selected car via links, so may be relevant.
Markings (K) on coupling (1) and pipe (4) must be flush.
Push quick-connect coupling (1) onto pipe (4) until a "click" can clearly be heard.
To check that quick-connect coupling (1) has been installed correctly, pull it back forcefully.