U0100

DTC U0100-U0299

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.





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

Step 1 - Step 7:

Step 8:

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.
8. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.