A redundancy control system and method of transmitting computational data are provided, for detection of transmission errors and failure diagnosis, including generating first computational data and generating first generated data using a first generation algorithm for error detection; generating second computational data and generating second generated data using a second generation algorithm for error detection; comparing the first/second computational data; transmitting transmission data including coincident computational data and the first/second generated data; generating, in the receiving device, computational data and third/fourth generated data from preset first/second generation algorithms; and comparing the first/third generated data and the first/third generated data, and detecting the presence or absence of an error in the received computational data.