The present document describes the Diameter-based V4 interface between the V2X Control Function and the Home Subscriber Server (HSS) defined for V2X services. This specification defines the Diameter application for V4 reference point between the V2X Control Function and the HSS. The interactions between the V2X Control Function and the HSS are specified. The stage 2 description for V2X service features in EPS is specified in 3GPP TS 23.285 [2].