Data Link Communications System

CIRCUIT DESCRIPTION




During normal vehicle operation modules connected to the class 2 serial data circuit monitor the class 2 serial data circuit for serial data communications. Operating information and commands are exchanged among the modules. When a module receives a critical operating parameter message, the module records and learns the identification number of the transmitting module for the purpose State of Health monitoring. A critical operating parameter is one which, when not received, requires that the receiving module use a default value for that parameter. Once an identification number is learned by a module, it will monitor the class 2 serial data circuit for that module's Node Alive message. Each module on the class 2 serial data circuit is required to send a Node Alive message every 2 seconds. If no message is detected from a learned identification number for 5 seconds, a DTC U1XXX, where XXX is equal to the three digit identification number is set.

CONDITIONS FOR RUNNING THE DTC
^ The following diagnostic trouble codes do not have a current status:
- B1327
- B1328
- B1982
- B1983
- U1300
- U1301
- U1305
^ The vehicle power mode requires serial data communication to occur.

CONDITIONS FOR SETTING THE DTC
At least one critical operating parameter has not been associated with an identification number within about 5 seconds after beginning class 2 serial data communication.

CONDITIONS FOR CLEARING THE DTC
^ A current DTC clears when the malfunction is no longer present.
^ A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DIAGNOSTIC AIDS
When multiple Loss of Communication DTCs are set concurrently, the cause is likely to be 2 opens in the ring portion of the class 2 serial data circuit. Use the Control Module ID Number list in order to determine which modules are not communicating. Use the class 2 serial data circuit schematic in order to determine the location of the opens.

TEST DESCRIPTION

Steps 1-4:

Steps 5-10:

The number below refers to the step number on the diagnostic table.
8. The module which was not communicating on the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.