| Table 1: | GMLAN ID |
Circuit Description
Modules connected to the GMLAN 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 GMLAN 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 not communicating.
If any of the GMLAN circuits are shorted to battery voltage, ground or between them, no communication is possible on GMLAN serial data bus, and a DTC U0073 sets.
Control Module | ID Number |
|---|---|
Engine Control Module (ECM) | 0100 |
Glow Plug Control Module | 0106 |
Transmission Control Module (TCM) | 0101 |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC U01XX through U02XX Lost Communication With XX Module
Conditions for Running the DTCs
| • | DTC U0073 is not set. |
| • | The ignition switch is ON. |
| • | The module supply voltage is in the normal operating range of 9-16 volts. |
Conditions for Setting the DTC
A receiving module did not detect the GMLAN serial data supervised periodic message from a transmitting module.
Action Taken When the DTC Sets
| • | The module uses a default value for the missing parameter. |
| • | The malfunction indicator lamp (MIL) will illuminate on the second consecutive ignition cycle that the diagnostic runs and fails, for the type B DTCs. For a detailed description about DTCs types refer to Diagnostic Trouble Code (DTC) Type Definitions for the 6.6L (LLY) engine. |
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 for the 6.6L (LLY) engine. For information about DTC type refer to Diagnostic Trouble Code (DTC) Types for the 6.6L (LLY) engine.
| • | 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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
A total loss of communication on GMLAN serial data link should be diagnosed first.
-
The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
Step | Action | Yes | No | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Computer/Integrating Systems Connector End Views | |||||||||||||||||||
Is DTC U0073 set as current? | Go to DTC U0073 | Go to Step 2 | |||||||||||||||||
2 |
Important: Use the control module ID number list in order to determine which module is not communicating on GMLAN serial data bus.
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 GMLAN serial data circuits of the module that is not communicating on GMLAN serial data bus for an open. Refer to Circuit Testing and Wiring Repairs . 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 GMLAN 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 GMLAN 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 Communications DTC set. Does the scan tool display any DTCs which do not begin with a "U"? | Go to Step 8 | |||||||||||||||||
Did you complete the action? | -- | ||||||||||||||||||
