This tool monitors the J1708 and J1939 data links and indicates component data activity such as engine controller, transmission controller, brake controller, and IP, cluster, and body controllers. The DLMU unit attaches to the 9-pin off board diagnostic connector located in the cab of the vehicle. PLEASE NOTE: This device connects to a BLACK 9-PIN Mating Connector. It does not connect to a GREEN 9-PIN Mating Connector.