212 589 00 90 00 Test adapter - WS46.00-P-0101B
WARNING: This page is about a different car, the 2012 Mercedes-Benz C300, 2011 Mercedes-Benz C300, 2010 Mercedes-Benz C300, 2009 Mercedes-Benz C300, and 2008 Mercedes-Benz C300. However, it is still accessible from the selected car via links, so may be relevant.