This high bandwidth differential PCI fault insertion card is designed to simulate common faults on high speed two wire communication interfaces such as Ethernet. This card supports 4 or 8-channels of two wire serial connections and can be used for simulating faults on Ethernet, AFDX, BroadR-Reach, 100BaseT and 1000BaseT interfaces. Any wire can be set to an open circuit, shorts can be applied across the wire pair, or to the adjacent pair. Fault connections can be made to one of four external signals via two fault buses, typically simulating connections to a supply voltage or ground. Each fault bus is capable of carrying 2A allowing multiple channels to be connected to the same fault condition. Additionally, each fault bus features a changeover relay to allow the user to connect alternative fault conditions to the fault buses.