Data Link Communications
DTC U1040CIRCUIT 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 3 digit identification number is set.
CONDITIONS FOR RUNNING THE DTC
- The following DTCs do not have a current status:
- B1327
- B1328
- U1300
- U1301
- U1305
- The vehicle power mode requires serial data communication to occur.
CONDITIONS FOR SETTING THE DTC
A node alive message has not been received from an unidentified module within the last 5 seconds after establishing 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
Step 1:
Steps 2-4:
Steps 5-8:
The number below refers to the step number on the diagnostic table.
6. 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.