An electrically controllable electromechanical inlet valve (2a) which is closed in the currentless state and is held in the closed state by the force of a spring (2b), an outlet valve (5a), and a displacement element (6), the inlet valve is operated in a self-controlling operating mode after a start command is present. In the self-controlling operating mode, the rail pressure is built without knowledge of the phase position of the displacement element. During the self-controlling operating mode, the phase position of the displacement element is determined. After the phase position of the piston or displacement element is determined, the inlet valve is switched over to a non-self-controlling operating mode.