WARNING: This page is about a different car, the 2013 BMW X5 M, 2012 BMW X5 M, 2011 BMW X5 M, and 2010 BMW X5 M. However, it is still accessible from the selected car via links, so may be relevant.
0491385 170001 Adapter MW
NOTE:
(Adapter) For checking the pressure relief valve in the radiator cap / Series: all except E28 [Discontinued]