An electronically controlled pneumatic (ECP) overlay control valve can selective switch between a conventional pneumatic mode and an ECP mode. In ECP mode, the overlay control valve shunts the brake cylinder pressure of the pneumatic control valve which allows a relay valve to build or exhaust pressure in the brake cylinder in response to an electronically controlled apply/release circuit. In conventional pneumatic mode, the overlay control valve disconnects the relay valve and allows a conventional pneumatic control valve to control the pressurization and exhausting of the brake cylinder.