Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC U1000: Class 2 Data LinkDTC U1255: Loss of Class 2 Communication
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|
Battery Positive Voltage Circuits | U0100-U0299 | U0100-U0299 | -- |
Ignition Voltage Circuits | U0100-U0299 | U0100-U0299 | -- |
Module Ground Circuits | -- | U0100-U0299 | -- |
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 (SOH) monitoring. 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 one critical parameter within about 5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. If more than one critical parameter does not have an identification number association, the DTC will only be reported once.
Conditions for Running the DTC
| • | Voltage supplied to the module is in the normal operating voltage range of 9-16 volts. |
| • | Diagnostic trouble codes U1300, U1301, and U1305 do not have a current status. |
| • | The module operation or the vehicle power mode requires serial data communication to occur. |
Conditions for Setting the DTC
At least one critical operating parameter has not been associated with an identification number within about 5 seconds after beginning 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 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 DTC U1000 will clear after 50 ignition switch ON/OFF cycles with no repeat of the failure. |
Diagnostic Aids
If a malfunction such as an open fuse to a module occurs while serial data communication is active, a Lost Communication DTC for the specific module is set as a current DTC in other modules. When all serial data communication becomes inactive, the current Lost Communication DTC is cleared, but the history DTC remains. When serial data communication resumes, the module with the open fuse will not be learned by the other modules, so DTC U1000 or U1255 is set as current by the other modules. A lost communication DTC for a specific module set as history along with a DTC U1000 or U1255 will identify the likely module with the loss of communication.
In the event of a malfunction occurrence while serial data communication is inactive, DTC U1000 or U1255 is set without a loss of communication DTC for the specific module.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for Scan Tool Information
Circuit/System Verification
Verify that no DTC within the range of U1001-U1254 exists as current or history in any module.
Important: If the U1001-U1254 DTC is set in history it may still not be communicating.
| ⇒ | If any DTC within the range of U1001-U1254 does exist, refer to Diagnostic Trouble Code (DTC) List - Vehicle. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for module replacement, setup, and programming |
