U1000 - Class 2 Communication Malfunction

DTC U1000 Class 2 Communication Malfunction (Part 1 Of 2):

DTC U1000 Class 2 Communication Malfunction (Part 2 Of 2):

CIRCUIT DESCRIPTION
For a view of the system schematic, refer to Data Link Connector (DLC) Schematics.

Modules connected to the class 2 serial data link monitor the link 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. When a module does not associate an identification number with at least 1 critical parameter within about five seconds of beginning class 2 communication, DTC U1000 is set. When more than 1 critical parameter does not have an identification number associated with the critical parameter. U1000 will only be reported once.

CONDITIONS FOR SETTING THE DTC
^ Voltage supplied to the module is in the normal operating voltage range (approximately 9-16 volts).
^ DTC U1301 is not current.
^ At least 1 critical operating parameter has not been associated with an identification number.
^ The above conditions are all met simultaneously for the first 5 seconds after beginning Class 2 communication.

ACTION TAKEN WHEN THE DTC SETS
^ The module uses a default value for the missing parameter.
^ DTC U1000 is set by the module.

CONDITIONS FOR CLEARING THE DTC
^ A current U1000 will clear when all the critical operating parameters for the module have been associated with an identification number or at the end of the current ignition cycle.
^ A history U1000 will clear upon receipt of a scan tool (clear DTCs) command.

DIAGNOSTIC AIDS
When a malfunction (such as a blown fuse to a module) occurs while the modules are communicating a Lost Communication DTC is set current. When the modules stop communicating (ignition switch is turned to OFF), the current Lost Communication DTC clears but the history DTC remains. When the modules begin to communicate again, the module with the blown fuse will not be learned by the other modules so U1000 is set current by the other modules. It the malfunction occurs when the modules are not communicating, only U1000 is set.

TEST DESCRIPTION
1. This test inspects whether the malfunction occurred during an ignition cycle. It the malfunction did, then additional information is available in order to aid in diagnosis.
3. This test determines whether any modules on the class 2 serial data link are not communicating. If all modules are communicating, the DTC may not be valid.
4. This step verifies that the module which does not communicate is powered and will not communicate via the class 2 serial data link.
5. This test inspects for an improper connection to the module preventing class 2 serial communication.
6. This test determines whether the malfunction is due to the class 2 serial data circuit or due to a malfunctioning control module.
7. This test inspects for an improper connection to SP205 preventing class 2 serial communication.
8. This test determines whether the malfunction is due to the class 2 serial data circuit or due to a malfunction in splice pack SP205.
13. The module which did not communicate due to a class 2 serial data circuit malfunction may have set the Lost Communication DTCs for those modules that the module was monitoring.
15. Since the modules which can communicate indicate the module which cannot communicate, it is necessary to clear the DTC from these modules to avoid future misdiagnosis.
18. This test inspects for other malfunctions which may have caused DTC U1000 to set.
20. This test determines whether DTC U1000 was set due to malfunction in the module which set the DTC.