the invention provides a bus driver failure detection system which facilitates detection of a failure of a bus driver from which data are sent out to a bus . the bus driver failure detection system includes a plurality of bus drivers for sending out signals to a single bus , at least one receiver connected to the bus , and an impedance control circuit for controlling the bus so that , upon testing , the bus does not exhibit a high impedance state . the impedance control circuit may be constructed as a circuit which holds a value of the bus in response to a test signal .