Method of manufacturing containers by blow-molding in a mold starting from a plastic blank, involving, when manufacturing a container: —a step of introducing a blank into a mold; —at least a step of placing the inside of the blank in communication with at least one fluid circuit by an solenoid valve associated with the circuit; —at a predetermined moment, referred to as the solenoid valve opening pulse (TEV1; . . . ; TEV4), sending a command to open to the solenoid valve which has a theoretical opening delay (Dt1; . . . ; Dt4), the method including steps involving: —calculating the actual opening delay (De1; . . . ; De4) of the solenoid valve; —calculating a difference (Δt1; . . . ; Δt4) between the actual opening delay (De1; . . . ; De4) and the theoretical opening delay (Dt1; . . . ; Dt4); and—if the calculated difference is greater than a maximum permissible difference, emitting notification that a maximum permissible difference has been exceed.