Circuit Description
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 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 five seconds of beginning Class 2 communication, DTC U1000 is set. When more than one critical parameter does not have an identification number associated with it, 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). |
| • | 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 MIL/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 DTCs" command. |
Diagnostic Aids
When a malfunction (such as a blown fuse to a module) occurs while modules are communicating a Lost Communication DTC is set current. When the modules stop communicating (Ignition switch is turned off) the current Lost Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the module which 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
The number(s) below refer to the step number(s) on the diagnostic table.
-
This test determines if the malfunction occurred during an ignition cycle. If it did, then additional information is available to aid in diagnosis.
-
This test determines if any modules on the Class 2 serial data link are not communicating. If all modules are communicating, the DTC may not be valid.
-
This step verifies that the module which does not communicate is powered and will not communicate via the Class 2 serial data link.
-
This test determines if the malfunction is due to the Class 2 serial data circuit or due to a malfunctioning control module.
-
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 it was monitoring.
-
Modules which can communicate indicate the module(s) which cannot communicate. In order to avoid future misdiagnosis, the DTC must be cleared from these modules.
-
This test determines if there are other malfunctions which may have caused DTC U1000 to set.
-
This test determines if DTC U1000 was set due to a malfunction in the module which set the DTC.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Tools Required
| ||||||||
1 | Was the Data Link Connector System Check performed? | -- | Go to Step 2 | |||||
Are there any history DTCs in the range of U1001 to U1199 also present? | -- | Go to Step 3 | Go to Step 4 | |||||
3 | Diagnose the malfunction using the Class 2 Lost Communications With XXX (U1xxx) procedure. Is the procedure complete? | -- | -- | |||||
Are there any modules on the Class 2 serial data link that are not communicating? | -- | Go to Step 5 | Go to Step 16 | |||||
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? | -- | Go to Step 11 | Go to Step 6 | |||||
Is the resistance within the specified range? | 0-5 ohms | Go to Step 10 | Go to Step 7 | |||||
7 |
Is the resistance within the specified range? | 0-5 ohms | Go to Step 9 | Go to Step 8 | ||||
8 | Repair open Class 2 Serial Data CKT. Refer to Wiring Repairs in Wiring Systems. Did you complete the Repair? | -- | Go to Step 11 | -- | ||||
9 |
Did you complete the repair? | -- | Go to Step 11 | -- | ||||
10 |
Is the repair complete? | -- | Go to Step 11 | -- | ||||
Are there any DTCs which do not begin with a U set? | -- | Go to Step 12 | Go to Step 13 | |||||
12 | Diagnose the DTCs as directed by the diagnostic procedures for the particular module. Is the procedure complete? | -- | Go to Step 13 | -- | ||||
Check for DTCs in the module(s) which had U1000 set as a current DTC. Are there any DTCs that do not begin with a U set? | -- | Go to Step 15 | Go to Step 14 | |||||
14 | Clear the DTCs. Is the procedure complete? | -- | -- | |||||
15 | Diagnose the DTCs as directed by the diagnostic procedures for the particular module. Is the procedure complete? | -- | Go to Step 18 | -- | ||||
Are there any other DTCs present in the module which set U1000? | -- | Go to Step 17 | Go to Step 18 | |||||
Diagnose the DTCs as directed by the diagnostic procedures for the particular module. Is the procedure complete? | -- | Go to Step 18 | -- | |||||
18 |
Is DTC U1000 current? | -- | Go to Step 19 | |||||
19 |
Is the repair complete? | -- | -- | |||||
