A brake system (1) for a commercial vehicle (100) with a trailer includes a trailer control valve (24), a supply pressure line (46), a control pressure line (44), a valve arrangement for selectively connecting either the supply pressure line (46) or the control pressure line (44) to the trailer control valve (24), and an electronic control unit (10) that is arranged to perform electronic brake control. The valve arrangement is embodied as a structural valve unit (40), that can be switched by the electronic control unit (10) between the switching states connecting a trailer-side pressure line (52) to the control pressure line (44), and connecting the trailer-side pressure line (52) to the supply pressure line (46), and is arranged to subject the trailer-side pressure line (52) to a control pressure in a brake control situation depending on corresponding commands of the electronic control unit (10).