The present invention is directed toward a cellular phone that connects to an existing vehicle data link to perform the functions of an off-board device, such as a scan tool, for displaying diagnostic information relating to vehicles. In addition, the cellular phone connects to a starter/charger system and/or a battery to perform the functions of a starter/charger/battery testing device. Such a device allows a user to connect the cellular phone to a data link connector located in a vehicle, download software to either an adaptor or the cellular phone, retrieve information relating to diagnostic tests on the vehicle and view the results on the cellular phone display, and/or communicate the results to another person or device.