There are 2 data lines that can be accessed with a scan tool. The serial data line UART (CKT 800) allows the scan tool (when connected) and the following systems to communicate via the serial data:

The serial data line class 2 (CKT 1807) allows a scan tool to directly access the powertrain control module to read emissions related information. A scan tool can gain access to both data lines through the data link connector (DLC). Then, systems operations can be monitored or controlled for diagnostic purposes.