Data Link Communications

DTC U1001-U1254

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 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 a module with a learned identification number within the last 5 seconds.

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

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.