| Table 1: | GMLAN ID |
Circuit Description
Modules connected to the controller area network (CAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about messages exchanged on the serial data circuits. The supervised and periodic messages are used by the receiving module as an availability indicator from the transmitter module. Each message contains the identification number of the transmitting module. When a message indicates availability of the transmitting module is not received, the receiving module sets a DTC Uxxxx; where xxxx is equal to the 4-digit transmitter module identification number.
The control module ID number list below provides a method for determining which module is not communicating. A module with a CAN serial data circuits malfunction, or which loses power during the current ignition cycle, will set a Loss of Communication DTC by other modules requiring information from the failed module. The modules able to communicate will set a DTC Uxxxx indicating the module is not communicating.
If any of the CAN circuits are shorted to battery voltage, ground or between them, no communication is possible on the CAN serial data bus, and the engine control module (ECM) sets a U2104 or U2100.
Control Module | ID Number |
|---|---|
Engine Control Module (ECM) | 2105 |
Transmission Control Module (TCM) | 2106 |
Electronic Brake Control Module (EBCM) | 2108 |
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC U2105 Lost Communications With Engine Control System |
| • | DTC U2106 Lost Communications With Transmission Control System |
| • | DTC U2108 Lost Communications With ABS/TCS Control System |
Conditions for Running the DTCs
| • | The ignition is in the RUN position. |
| • | The module supply voltage is in the normal operating range of 9-16 volts. |
Conditions for Setting the DTC
| • | A receiving module for the past 125 milliseconds did not detect the CAN serial data bus message from a transmitting module. |
| • | DTC U2100 is not present. |
| • | DTC B1365 is not present. |
Action Taken When the DTC Sets
The module uses a default value for the missing parameter.
Conditions for Clearing the MIL/DTC
The malfunction indicator lamp (MIL) or DTC clearing depends on DTC type. For a detailed description about DTCs types, refer to Diagnostic Trouble Code (DTC) Type Definitions in Engine Controls - 6.6L (LLY). For information about DTC types, refer to Diagnostic Trouble Code (DTC) Types in Engine Controls - 6.6L (LLY).
| • | DTC Type C |
| - | A current DTC and MIL clear when the malfunction is no longer present. |
| - | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction. |
| • | DTC Type B |
| - | A current DTC clears when the malfunction is no longer present. |
| - | The MIL clears after three ignition cycles when the malfunction is no longer present. |
| - | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction. |
Diagnostic Aids
| • | A poor connection at the inoperative module may cause this code to set. |
| • | An improperly powered module may cause this code to set. |
| • | A code may self-extinguish when messages from the missing module are received. |
Step | Action | Yes | No | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Computer/Integrating Systems Connector End Views | |||||||||||||||||||||||
1 |
Is DTC U2100 or U2104 set as current? | Go to DTC U2100 | Go to Step 2 | ||||||||||||||||||||
2 |
Important: Use the control module ID number list in order to determine which module is not communicating on controller area network (CAN) serial data bus. Test the following circuits of the module that is not communicating on CAN serial data bus for an open or a short to ground:
Refer to the following:
Did you find and correct the condition? | Go to Step 7 | Go to Step 3 | ||||||||||||||||||||
3 |
Refer to the following:
Did you find and correct the condition? | Go to Step 7 | Go to Step 4 | ||||||||||||||||||||
4 | Test the CAN serial data circuits of the module that is not communicating on CAN serial data bus for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 7 | Go to Step 5 | ||||||||||||||||||||
5 | Inspect the harness connectors of the module that is not communicating on CAN serial data bus for poor connections and terminal tension at the following circuits:
Refer to the following:
| Go to Step 7 | Go to Step 6 | ||||||||||||||||||||
6 | Replace the module that is not communicating on CAN serial data bus. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 7 | -- | ||||||||||||||||||||
7 | Select the display DTCs function for the modules which had the loss of communication DTC set. Does the scan tool display any DTCs which do not begin with a U? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | Go to Step 8 | ||||||||||||||||||||
8 |
Did you complete the action? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | -- | ||||||||||||||||||||
