Circuit Description
Each module connected to the class 2 serial data circuit monitors 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. 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, it will monitor for that modules node alive message. Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a 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 U1001-U1254 is set.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC U1016 Lost Communications With Powertrain Control Module (PCM) |
| • | DTC U1026 Lost Communications With Transfer Case Control Module (TCCM) |
| • | DTC U1041 Lost Communications With Electronic Brake Control Module (EBCM) |
| • | DTC U1064 Lost Communications With Body Control Module (BCM) |
| • | DTC U1088 Lost Communications With Sensing and Diagnostic Module (SDM) |
| • | DTC U1096 Lost Communications With Instrument Panel Cluster (IPC) |
| • | DTC U1128 Lost Communications With Radio |
| • | DTC U1136 Lost Communications With Digital Audio Broadcast |
| • | DTC U1151 Lost Communications With OnStar |
Conditions for Running the DTC
| • | Battery Voltage is 9-16 volts. |
| • | DTCs U1300, U1301, or U1305 are not current. |
| • | The vehicle power mode requires serial data communication to occur. |
Conditions for Setting the DTC
A node alive message has not been received from a module with a learned identification number within the last 5 seconds.
Action Taken When the DTC Sets
The module uses a default value for the missing parameter.
Conditions for Clearing the DTC
| • | A current DTC clears when the malfunction is no longer present. |
| • | A history DTC clears when the ignition has been cycled 100 times, without a repeat of the malfunction. |
Diagnostic Aids
The following conditions may cause this DTC to set:
| • | An intermittent open between a module and a star connector |
| • | A poor connection at a module or a star connector |
| • | An intermittent open in a star connector |
| • | An open voltage or ground circuit to a module |
| • | An internal module malfunction |
When more than one Loss of Communication DTC is set in either one module of in several modules, diagnose the DTCs in the following order:
- Current DTCs before history DTCs unless told otherwise in the diagnostic tables.
- The DTC which is reported the most times.
- From the lowest number DTC to the highest number DTC.
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Yes | No | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems | |||||||||||||||||||||||
1 |
Important: Use the control module ID number list in order to determine which module is not communicating. Test the following circuits of the module that is not communicating for an open or a short to ground:
Refer to the following:
Did you find and correct the condition? | Go to Step 6 | Go to Step 2 | ||||||||||||||||||||
2 |
Refer to the following:
Did you find and correct the condition? | Go to Step 6 | Go to Step 3 | ||||||||||||||||||||
3 | Test the class 2 serial data circuits of the module that is not communicating for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 6 | Go to Step 4 | ||||||||||||||||||||
4 | Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits:
Refer to the following:
Did you find and correct the condition? | Go to Step 6 | Go to Step 5 | ||||||||||||||||||||
5 |
Important: Perform the programming or set up procedure for the module, if required. Replace the module that is not communicating. Refer to Control Module References for the applicable replacement procedure. Did you complete the replacement? | Go to Step 6 | -- | ||||||||||||||||||||
Does the scan tool display any DTCs which do not begin with a "U"? | Go to Control Module References for the applicable Diagnostic System Check | Go to Step 7 | |||||||||||||||||||||
7 | Select the Display DTCs function for the modules which had the Loss of Communications DTC set. Does the scan tool display any DTCs which do not begin with a "U"? | Go to Control Module References for the applicable Diagnostic System Check | Go to Step 8 | ||||||||||||||||||||
8 |
Did you complete the action? | Go to Control Module References for the applicable Diagnostic System Check | -- | ||||||||||||||||||||
