Intermittent bus faults
WARNING: This page is about a different car, the 2003 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
The ECM and TCM continuously check that all the control modules from which they receive information are communicating correctly. In the event of an intermittent fault in bus communication with one of these systems, DTCs will be generated in the ECM and TCM. The reason for the fault may be the bus leads or that the control module in question lacks power.