DTC U1064: Lost Communications With Body Multiple Control System: Notes
Class II serial data is a 0 to 7 volt variable pulse width message scheme (logic 0's and logic l's) used to communicate information between modules and for communication to an off-board Scan tool. Contained in each module memory is a list of serial data messages and default actions taken by the module if one of the important messages is not received. One of the most important messages is the State Of Health (SOH) message used to inform each module that other modules on the Class II link are functioning correctly.
Each module on the Class II link must first "learn" all modules connected to the Class II link every time the ignition is turned On. Each message that a module sends out on the link contains a source identifier used to identify where the information came from. Once a module receives information, it will store the attached controller ID. If this same information is not received later in the ignition cycle, lost communications with a specific controller DTC will set. DTC U1064 sets when a controller does not receive specific information from the BCM after it had already learned its source ID in that ignition cycle.