Checking Pressure Relief Valve In Cap:
WARNING: This page is about a different car, the 2005 BMW 645Ci and 2004 BMW 645Ci. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Coolant residue can cause the pressure relief valve in the cap to stick, therefore repeat the check procedure on the cap 2-3 times.
Screw cap (1) onto special tool 17 0 114.
Build up pressure with special tool 17 0 101 (hand pump);
observe pressure gauge to ascertain when opening pressure is achieved.
Opening pressure of pressure relief valve.