A diagnostic tool for a vehicle configured to automatically identify different communication protocols used by Electronic Control Units (ECUs) on-board the vehicle. The diagnostic tool includes a connector connectable to a data port of the vehicle; a data processor and a data storage device configured to store a list of different communication protocols. The data processor automatically initiates communications with the ECUs on-board the vehicle using a first communication protocol and if the data processor receives a response comporting to the first communication protocol, the data processor determines that at least one ECU on-board the vehicle is using the first communication protocol. Additionally, the data processor automatically initiates communications with the ECUs on-board the vehicle using a second communication protocol and if the data processor receives a response comporting to the second communication protocol, the data processor determines that at least one ECU on-board the vehicle is using the second communication protocol.