U1000

Circuit Description
The link for serial data communications during normal vehicle operation is monitored by the modules connected to the Class 2 serial data link. Operating information and commands are exchanged among the modules. The identification number of the module that sent the message for the State of Health monitoring (Node Alive messages) is recorded when a module receives a message for a critical operating parameter. A critical operating parameter is one that (when not received) requires that the module use a default value for that parameter. DTC U1000 is set when a module does not associate an identification number with at least one critical parameter within about 5 seconds of beginning Class 2 communication. U1000 will only be reported once when more than one critical parameter does not have an identification number associated with the parameter.

Conditions for Setting the DTC
- The voltage is supplied to the module in the normal operating voltage range of approximately 9-16 Volts.
- DTC U1301 is not current when setting the DTC.
- At least one 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 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 DTC's command.

Diagnostic Aids
The DTC is set current when a malfunction occurs while modules are communicating a lost communication. A malfunction may include a blown fuse to a module. The current lost communication DTC is cleared. The history DTC remains under the following conditions:
- The modules stop communicating.
- The ignition is turned to the OFF position.

The module with the blown fuse will not be learned by the other modules. DTC U1000 is set current by the other modules once the modules begin to communicate again. Only DTC U1000 is set if the malfunction occurs when the modules are not communicating. Refer to intermittent and poor connections.

Steps 1 - 4:

Steps 5 - 7:

Steps 8 - 13:

Steps 14 - 20:

Steps 21 - 23:

Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
1. This test checks whether the malfunction occurred during an ignition cycle. If the malfunction occurred during an ignition cycle, 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 checks 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.w
7. This test checks for an improper connection to SP201 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 SP201.
13. The module which did not communicate due to a Class 2 serial data circuit malfunction may have set lost communication DTCs for those modules that were being monitored.
15. Since the modules which can communicate indicate the module which cannot communicate, you will need to clear the DTC from these modules in order to avoid future misdiagnosis.
18. This test checks for other malfunctions which may have caused DTC U1000 to set.
20. This test determines if DTC U1000 was set due to a malfunction in the module that set the DTC.