The invention concerns an electronic parking brake system (2), comprising an air supply (4), a check valve (6), connected to the air supply, an electro-pneumatic control unit (8), at least one park brake actuator (10), a relay valve (12), comprising a first port (12a) connected to the check valve, a second port (12b) connected to the electro-pneumatic control unit, a third port (12c) connected to the park brake actuator and a fourth port (12d) which is in communication with the atmosphere, and an electrically actuated valve (14), which is controlled by the electro-pneumatic control unit (8) and which includes a first orifice (14a) connected to a compressed air line (16) extending between the check valve and the air supply, a second orifice (14b), a third orifice (14c) connected to the electro-pneumatic control unit (8), and preferably a vent orifice. The second orifice (14b) is connected to another compressed air line (18) extending between the check valve (6) and the first port (12a) of the relay valve (12).