Systems, methods, and devices for fault detection and tolerance in a downhole tool string are provided. If a fault is detected in an electrical path between tools of downhole tool string, one or more switches of a fault detection and tolerance circuit may be kept open to isolate the fault in an electrical path between tools of downhole tool string. If a fault is not detected, one or more switches of a fault detection and tolerance circuit may be closed to enable the transmission of signals on the electrical path. In some embodiments of fault detection and tolerance circuits, an additional one or more switches may be kept open to isolate the fault in electronics of the tool.