The GMLAN serial data circuits are controller area network (CAN) high and/or low speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. There are two different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. The GMLAN serial data circuits also communicate directly to the data link connector (DLC). Messages are interpreted by the externally connected CANdi module which acts as a transceiver for the scan tool.

Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules. All the modules on the GMLAN networks, maintain 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.

This diagnostic procedure supports the following DTCs:

The module setting the DTC has attempted to establish communications on the GMLAN circuits for more than 7 times.

This DTC cannot be retrieved with a current status. Diagnosis of a current DTC is accomplished via Scan Tool Does Not Communicate with High Speed GMLAN Device . Refer to Data Link References for the correct procedure for the specific module(s) and the busses they use to communicate.