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Test Description

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table:

  1. 6:  The module which was not communicating due to an open in the GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.
  2. 8:  The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
DTC U2105

Step Action Yes No
1
  1. Turn the ignition OFF.
  2. Test the following circuits of the module that is not communicating for an open or a short to ground.
    • The battery positive circuits
    • The battery voltage output circuits
    • The ignition positive voltage circuits
    • The ignition voltage output circuits
Refer to Data Link Connector (DLC) Schematics  for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.Did you find and correct the condition?		 Go to Step 8  Go to Step 2 
2 Test the ground circuits of the module that is not communicating for an open. Refer to Data Link Connector (DLC) Schematics  for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 8  Go to Step 3 
3 Test the GMLAN serial data circuits of the module that is not communicating for an open. Refer to Data Link Connector (DLC) Schematics  for the applicable schematic. 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 Test the following circuits of the module that is not communicating for poor connections:
  • The battery positive voltage circuits
  • The battery voltage output circuits
  • The ignition positive voltage circuits
  • The ignition voltage output circuits
  • The ground circuits
  • The GMLAN serial data circuits

Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 8  Go to Step 5 
5
IMPORTANT: Perform the module setup procedure if required.
Replace the module that is not communicating. Refer to Control Module References in Body Control Systems.Did you complete the replacement?		 Go to Step 8  -
6 
  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. Select the Display DTCs function for the module which was not communicating.
Does the scan tool display any DTCs which do not begin with a "U"?		 Go to the Control Module References for the applicable Diagnostic System Check Go to Step 7 
7 Use the scan tool in order to clear the DTCs.
Did you complete the action?		 Go to Step 8  -
8  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 the Control Module References for the applicable Diagnostic System Check Go to Step 9 
9
  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?		 System OK -
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