OBD II regulations require that all vehicle manufacturers establish a common communications system called Class II data. Each bit of information in Class II data can have one or two lengths, long or short. This feature allows a Scan Tool to access communication data from any make or model vehicle sold with Class II data capability.
This feature allows vehicle wiring to carry multiple signals over a single wire. Messages carried on Class II data streams can be prioritized. If two messages attempt to establish communication on the data line at the same time, only the message with the higher priority will continue. The message with the lower priority must wait.