U1129

CIRCUIT DESCRIPTION
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for 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 for that modules node alive message. Each module on the class 2 serial data circuit is required to send a Node Alive message every 2 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1XXX. XXX is equal to the 3 digit identification number of the module.







The control module ID number list provides a method for determining which module is not communicating. A module with an internal class 2 serial data circuit malfunction or which loses power during the current ignition cycle would have a lost communication DTC set by other modules. Use the control module ID number list in order to determine which module is not communicating and the lost communications with XXX diagnostic table in order to diagnose the malfunction. When no message is detected from a learned identification number for 5 seconds, a DTC U1XXX is set.

When more than one loss of communication DTC is set in a single module or among multiple modules, diagnose the DTCs in the following order:
1. Current DTCs before history DTCs except as specified in the diagnostic tables.
2. The DTC which is reported the most times.
3. From the lowest number DTC to the highest number DTC.

CONDITIONS FOR RUNNING THE DTC
- Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
- DTCs U1300, U1301 or U1305 do not have a current status.
- 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.

ACTION TAKEN WHEN THE DTC SETS
The module uses a default value for the missing parameter.

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
- An intermittent open between a module and a star connector may cause this DTC to set.
- A poor connection at a module or a star connector may cause this DTC to set.
- An intermittent open in a star connector may cause this DTC to set.
- An open voltage or ground circuit to a module may cause this DTC to set.
- An internal module malfunction may cause this DTC to set.

TEST DESCRIPTION

Steps 1-2:

Steps 3-5:

Steps 6-8:

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.