If anyone is interested, here is a ScannerDanner video where he is troubleshooting a Module communication problem on an 05 Cobalt. You can pick up some interesting info on how the GMLAN communicates plus see why a lot of these issues are not as simple as some people would like the answers to be when trouble shooting some of our problems.
Troubleshooting a Bad TCM - CAN and Sensor Ground Circuit Problems - YouTube
This is a bad TCM module, but the same theory would apply to other modules.
Troubleshooting a Bad TCM - CAN and Sensor Ground Circuit Problems - YouTube
This is a bad TCM module, but the same theory would apply to other modules.