Circuit Description
For a view of the system schematic, refer to Data Link Connector 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. If the malfunction occurs when the modules are not communicating, only U1000 is set.
Test Description
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This test inspects whether the malfunction occurred during an ignition cycle. If the malfunction did, then additional information is available in order to aid in diagnosis.
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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.
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This test inspects for an improper connection to the module preventing class 2 serial communication.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Are any history DTCs in the range of U1001 to U1199 also present? | -- | |||
2 | Diagnose the malfunction using the class 2 Lost Communications With XXX (U1module) procedure. Is the procedure complete? | -- | System OK | -- |
Are there any modules on the class 2 serial data link which are not communicating? | -- | |||
Perform the Diagnostic System Check for the module which does not communicate to ensure that the module is properly powered. Was a repair made when the Diagnostic System Check was performed? | -- | |||
Is the connection good? | -- | |||
Measure the resistance of the class 2 serial data circuit from the connector of the module which does not communicate to the DLC terminal 2. Is the resistance within the specified range? | 0-5ohms | |||
Did you find a problem? | -- | |||
Measure the resistance of the class 2 serial data circuit from the connector of the module which does not communicate to the SP205. Is the resistance in the specified range? | 0-5ohms | |||
9 | Repair or replace the SP205. Refer to Data Link Connector Schematics . Is the repair complete? | -- | -- | |
10 | Replace the module which does not communicate. Refer to the appropriate On-Vehicle Service procedures for the module being replaced in order to ensure a complete repair. Is the repair complete? | -- | -- | |
11 | Repair the open in the class 2 serial data circuit of the module which does not communicate. Is the repair complete? | -- | -- | |
12 | Repair the connection as needed. Is the repair complete? | -- | -- | |
Are there any DTCs which do not begin with a U set? | -- | |||
14 | Diagnose the DTCs as directed by the diagnostic procedures for the particular module. Is the procedure complete? | -- | -- | |
Inspect for DTCs in the module(s) which had U1000 set as a current DTC. Are there any DTCs which do not begin with a U set? | -- | |||
16 | Clear the DTCs. Is the procedure complete? | -- | System OK | -- |
17 | Diagnose the DTCs as directed by the diagnostic procedures for the particular module. Is the procedure complete? | -- | -- | |
Are any other DTCs present in the module which set U1000? | -- | |||
19 | Diagnose the DTCs as directed by the diagnostic procedures for the particular module. Is the procedure complete? | -- | -- | |
Is DTC U1000 current? | -- | System OK | ||
21 | Replace the module which does not communicate. Refer to the appropriate On-Vehicle Service procedures for the module being replaced in order to ensure a complete repair. Is the repair complete? | -- | System OK | -- |
