Vehicle control system and abnormality diagnosis method

An abnormality diagnosis method for a vehicle control system including a master electronic control unit configured to output first time information serving as a reference, a plurality of slave electronic control units connected to the master electronic control unit via a network, and an abnormality diagnosis unit, the master electronic control unit and the slave electronic control units being configured to control a vehicle in cooperation, the abnormality diagnosis unit being configured to determine whether a synchronization abnormality has occurred between the first time information and second time information that is time information in each of the slave electronic control units, the abnormality diagnosis method comprising:

• a step of causing the master electronic control unit and each of the slave electronic control units to transmit and receive signals to acquire a first time that is the first time information when the master electronic control unit transmits a first signal to the slave electronic control unit, a second time that is the second time information when the slave electronic control unit receives the first signal, a third time that is the second time information when the slave electronic control unit transmits a second signal to the master electronic control unit in response to reception of the first signal, a fourth time that is the first time information when the master electronic control unit receives the second signal, a fifth time that is the first time information when the master electronic control unit transmits a third signal to the slave electronic control unit in response to reception of the second signal, and a sixth time that is the second time information when the slave electronic control unit receives the third signal;
• a step of calculating, by the slave electronic control unit, a delay time of transmission between the master electronic control unit and the slave electronic control unit based on the third time, the fourth time, the fifth time, and the sixth time;
• a step of determining, by the abnormality diagnosis unit, whether a periodic deviation that is a deviation between a clock period in the master electronic control unit and a clock period in the slave electronic control unit is present based on a processing period in the master electronic control unit that is a difference obtained by subtracting the previously acquired first time from the current first time, and a processing period in the slave electronic control unit that is a difference obtained by subtracting the previously acquired second time from the current second time;
• a step of determining, by the abnormality diagnosis unit, whether an offset deviation is present based on the first time and a difference obtained by subtracting the delay time from the second time when determination is made that the periodic deviation is not present;
• and
• a step of determining, by the abnormality diagnosis unit, that the synchronization abnormality has occurred when determination is made that the periodic deviation is present or that the offset deviation is present.