U1151

DTC U1151

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. 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 module's Node Alive message. Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction 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 where xxx is equal to the 3-digit identification number is set.




The control module ID number list provides a method for determining which module is not communicating. A module with a class 2 serial data circuit malfunction or which loses power during the current ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from that failed module. The modules that can communicate will set a DTC indicating the module that can not communicate.

When more than one Loss of Communication DTC is set in either one module or in several modules, diagnose the DTCs in the following order:
1. Current DTCs before history DTCs, unless told otherwise in the diagnostic table
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
- The following diagnostic trouble codes do not have a current status:
- U1300
- U1301
- U1305
- The vehicle power mode 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 5 seconds.

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 the inoperative module and a star connector may cause this code to set.
- A poor connection at the inoperative module or a star connector may cause this code to set.
- An intermittent open in a star connector may cause this code to set.
- An improperly powered module may cause this code to set.

TEST DESCRIPTION

Steps 1-8:

Step 9:

The number below refers to the step number on the diagnostic table.
7. 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.