GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Rendezvous - FWD 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 DTC U0100-U0299
Table 1: GMLAN High Speed ID

Circuit Description

Modules connected to the GMLAN High Speed 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. 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 High Speed 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 High Speed circuits are shorted to battery voltage, ground or between them, no communication is possible on GMLAN High Speed serial data bus, and a DTC U0073 sets.

GMLAN High Speed ID

Control Module

ID Number

Transmission Control Module (TCM)

0101

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC U0100 Unassigned
    • DTC U0299 Unassigned

Conditions for Running the DTCs
    • The ignition is ON and the engine is running.
    • 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 High Speed 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.

Conditions for Clearing the MIL/DTC

The MIL or DTC clearing depends on DTC type.

    • 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 3 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.

  1. A total loss of communication on the GMLAN high speed serial data link should be diagnosed first.

    2.

  2. 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

1

  1. Install a scan tool.
  2. Start the engine.
  3. Retrieve the DTCs from the engine control module (ECM).

Is DTC U0073 set as current?

Go to DTC U0001

Go to Step 2

2

Important: Use the control module ID number list in order to determine which module is not communicating on GMLAN high speed serial data bus.

  1. Turn ON the ignition, with the engine OFF.
  2. Test the following circuits of the module that is not communicating on GMLAN high speed serial data bus for an open or a short to ground:
    3. • The battery positive voltage input circuits
    • The battery positive voltage output circuits
    • The ignition voltage input circuits
    • The ignition voltage output circuits
    • The switched battery positive voltage circuits

Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Test the ground circuits of the module that is not communicating on GMLAN high speed serial data bus for an open.

Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4

Test the GMLAN high speed serial data circuits of the module that is not communicating on GMLAN high speed 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 GMLAN high speed serial data bus for poor connections and terminal tension at the following circuits:

    • The battery positive voltage input circuits
    • The battery positive voltage output circuits
    • The ignition voltage input circuits
    • The ignition voltage output circuits
    • The switched battery positive voltage supply circuits
    • The ground circuits
    • The GMLAN high speed serial data circuits

Refer to the following:

    •  Control Module References for the applicable schematic
    •  Connector Repairs in Wiring Systems

Go to Step 7

Go to Step 6

6

Important: Perform the programming or setup procedure for the module, if required.

Replace the module that is not communicating on GMLAN high speed serial data bus. Refer to Control Module References for the applicable replacement procedure.

Did you complete the replacement?

Go to Step 7

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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

Go to Step 8

8

  1. Use the scan tool in order to clear the DTCs.
  2. Continue diagnosing or clearing the DTCs until all the modules have been diagnosed and all the DTCs have been cleared.

Did you complete the action?

Go to Control Module References

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