Today's laws require that specific diagnostic information be made available on all vehicles manufactured on or after 1994 and sold in the United States. This information is typically available to a portable test device (Scan Tool) that is by necessity, external to the vehicle under test. Since this tool is not a part of the vehicle, it's very nature indicates that it should be portable and battery operated. Usually it is connected to the test vehicle's required female J1962 connector. The interface must conform to the standard pin assignments as designated by the appropriate SAE document.