Data Link Communications

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, the module records and identification number of the transmitting module for the purpose State of Health monitoring (Node Alive messages). A critical operating parameter is one which, when not received, requires that the 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
^ U1300
^ U1301
^ U1305
^ The vehicle power mode (ignition switch position) requires serial data communication to occur.

CONDITIONS FOR SETTING THE DTC
A message from a learned identification number has not been detected for the past five seconds.

CONDITIONS FOR CLEARING THE DTC
^ A current DTC will clear when a Node Alive message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.
^ A history DTC will clear upon receipt of a scan tool Clear DTCs command.

DIAGNOSTIC AIDS
When multiple Loss of Communication DTCs are set concurrently, the cause is likely to be two opens in 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 1-5:

Steps 6-10:

The numbers below refer to the step numbers on the diagnostic table.
4. The following modules have a single wire connection to the class 2 serial data circuit. An open in the single wire will prevent communications.
^ Audio Amplifier
^ Cellular Telephone Module W/UV8
^ Driver Door Module (DDM)
^ Driver Door Switch Assembly (DDSA)
^ Electronic Suspension Control (ESC)
^ Front Passenger Door Module (FPDM)
^ HVAC Control Module - Auxiliary
^ Left Middle Door Module (LMDM) W/V4U
^ Left Rear Door Module (LRDM)
^ Memory Seat Module (MSM)
^ Navigation Data Processor W/UY4
^ Radio W/UY4
^ Rear Integration Module (RIM)
^ Remote Control Door Lock Receiver (RCDLR)
^ Right Middle Door Module (RMDM) W/V4U
^ Right Rear Door Module (RRDM)
^ Steering Column Module W/N37
^ Theft Deterrent Control Module
^ Vehicle Interface Unit (VIU) W/UE1
^ Window Switch - Front Passenger W/armored car
7. The module which was not communicating due to an open in the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.

"For the description of RPO Code(s) shown in this article or any of the images therein, refer to the RPO Code List found at the Vehicle/Application and ID." RPO Codes