Circuit Description
For a full 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 (Node Alive messages). A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, the module will monitor for that module's Node Alive message. Each module on the class 2 serial data link which is powered and performing functions that require detection of communications malfunction is required to send a Node Alive message every 2 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx (where xxx is equal to the 3 digit identification number) is set.
Conditions for Setting the DTC
| • | Voltage supplied to the module is in the normal operating voltage range (approximately 9-16 volts). |
| • | DTC 1301 is not current. |
| • | A message from a learned identification number has not been detected for the past 5 seconds. |
Conditions for Clearing the DTC
| • | A current DTC U1xxx (where xxx is equal to the 3 digit identification number) will clear when a Node Alive message from the failed identification number is detected on the class 2 serial data link or at the end of the current ignition cycle. |
| • | A history DTC U1xxx will clear upon receipt of a scan tool Clear DTCs command. |
Diagnostic Aids
The control module identification number list provides a method for determining which module is not communicating. The diagnostic procedure assumes that all modules are powered. A module with an internal class 2 circuit malfunction or which loses power during the current ignition cycle would have a Lost Communication DTC set by the other modules. Use the control module identification number in order to determine which module is not communicating and the Lost Communication with XXX diagnostic table in order to diagnose the malfunction. The control module identification numbers are as follows:
Component | Identification Number |
|---|---|
Electronic Brake Module (EBCM) | 041 |
Automatic Transfer Case (ATC) Control Module | 026 |
Instrument Cluster (IPC) | None |
Body Control Module (BCM) | 016 |
Vehicle Control Module (VCM) | 016 |
The EBCM may set Class 2 Lost Communication DTCs when the BCM or the powertrain control module (PCM)/VCM is being reprogrammed. After reprogramming, test for DTCs in the ECCM. When only DTCs which begin with a U are set with a history status, clear the DTCs. Otherwise, diagnose the malfunction using the appropriate diagnostic table.
Test Description
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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 | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Perform the Diagnostic System Check for the module which does not communicate in order to ensure that the module is properly powered. Refer to the following for the appropriate Diagnostic System Check:
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 data link connector terminal 2. Is the resistance within the specified range? | 0-5ohms | |||||||||||||||
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 SP205. Refer to Data Link Connector Schematics . Is the resistance within the specified range? | 0-5ohms | |||||||||||||||
6 | Repair or replace the SP205. Refer to Data Link Connector Schematics . Is the repair complete? | -- | -- | |||||||||||||
7 | 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? | -- | -- | |||||||||||||
8 | Repair the open in the Class 2 serial data circuit of the module which does not communicate. Is the repair complete? | -- | -- | |||||||||||||
9 | Repair the connection as needed. Is the repair complete? | -- | -- | |||||||||||||
Are there any DTCs which do not begin with a U set? | -- | |||||||||||||||
11 | Clear the DTCs. Is the procedure complete? | -- | -- | |||||||||||||
Inspect for DTCs in each module which had the Class 2 Lost Communication DTCs set as a current DTC. Are there any DTCs which do not begin with a U set? | -- | |||||||||||||||
13 | Clear the DTCs. Is the procedure complete? | -- | System OK | -- | ||||||||||||
14 | Diagnose the DTCs as directed by the diagnostic procedures for the particular module. Is the procedure complete? | -- | -- |
