A control system enables a considerable decrease in electric power consumption
of backup power, leading to effective prevention of a dead battery, while data
in each control unit which need be maintained even after power is turned off is
properly maintained. An ECU has a first transmitter to transmit data which need
be maintained to an ECU for storage when a change in position of an IGSW connected
to a battery to the off position is detected, and a power supply cutoff circuit
to cut off the power supply to the other ECUs after the completion of the transmission
of data to the ECU for storage by the first transmitter, wherein the ECU for storage
has a first storage controller to store the data transmitted from the other ECUs
in RAM, and a power switching circuit to detect the change of the IGSW to the off
position and switch the power of the ECU for storage to the backup power.
