Perform the Diagnostic System Check - Vehicle.

The GMLAN serial data circuits are controller area network (CAN) 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. On this vehicle there are 2 totally different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. Refer to Data Link Communications Description and Operation for the complete description of these buses. The GMLAN serial data circuits also communicate directly to the DLC connector. 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. If the TEC value exceeds 255, the controller removes itself from the network and DTC U2100 will result.

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