GMLAN serial data circuit is CAN serial data bus, which is used to communicate information between each control module. Keep the normal data transmission speed high enough to ensure real time response as required. This vehicle is equipped with two different GMLAN serial data circuits, those are High Speed Dual-Circuited and Low Speed Single-Circuited. GMLAN serial data circuits are also communicating with Data Link Connector (DLC) directly. The information is interpreted by CANdi module which is connected outside and is equal to a scan tool receiver.

Each module connected to the GMLAN serial data circuit monitors the communication during normal vehicle operation, operating information is exchanged among modules during this procedure. Each module on GMLAN network supports a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages.

The module that sets DTC attempts to establish communication on GMLAN circuit more than 5 times or 5 seconds