A control system for adjusting functional elements of consecutive printing units of a multi-color, sheet-fed, rotary printing machine during its changeover from a first or face printing mode of operation to the first and second or back-up printing mode of operation. The system includes a first control circuit fed with data signals and clock pulse signals for controlling functional elements of a first printing unit, and a second control circuit for controlling functional elements of the subsequent printing unit. An auxiliary control circuit is arranged between the two control circuits and cooperates with a timing pulse adjuster which in turn is controlled by timing pulses from a timing pulse generator, from a sheet-control device and from a machine stop detecting device. The auxiliary control circuit is controlled by comparison pulses from the timing pulse generator and from a signal delivered by a switching unit activated simultaneously with the changeover from the first printing to the first and second printing mode of operation of the printing machine.