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Test Description

WARNING: This page is about a different car, the 2005 Chevrolet Malibu. 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. 3:  If body control module (BCM) will not power up the vehicle cannot establish the correct power mode. This step tests for the correct power supply conditions for the BCM.
  2. 4:  If DTC U2103 is set as history and you can communicate with the suspect module, the malfunction is an intermittent communication buss, power supply, ground or internal module connection.
  3. 5:  This step tests for the correct power supply conditions of the suspect module or modules.
  4. 6:  This step identifies which of the GMLAN busses the module or modules use for communication. Use the Data Link References  for identifying the correct buss to analyze.
  5. 11:  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.
  6. 20:  The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
DTC U2103

Step Action Yes No
Schematic Reference: Data Link Connector (DLC) Schematics 
Connector End View Reference: Master Electrical Component List in Wiring Systems
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Attempt to communicate with body control module (BCM).
Were you able to communicate with BCM?		 Go to Step 4  Go to Step 3 
3 
  1. Turn the ignition OFF.
  2. Disconnect the harness connectors from the BCM.
  3. Test the following circuits of the BCM harness connector for the indicated condition. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
    • Switched and constant B+ supply circuits, for power
    • Ground circuits, for continuity
    • All communications circuits, for continuity
Did you find and correct the condition?		 Go to Step 9  Go to Step 7 
4  Attempt to communicate with all of the modules on the vehicle.
Were you able to communicate with all of the modules?		 Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems Go to Step 5 
5  Test the following circuits of the modules that do not communicate:
  • Switched B+ supply circuits
  • Constant B+ supply circuits
  • Ground circuits

Did you find and correct the condition?		 Go to Step 9  Go to Step 6 
6 
  1. Refer to Data Link References  to identify the GMLAN buss or busses that the modules use to communicate and make a note.
  2. If more than one module is not communicating, use the data link connector (DLC) schematic to determine which module is closest to the DLC. Start the analysis at that module. Refer to Data Link Connector (DLC) Schematics .
  3. Disconnect the harness connectors from the non-communicating modules.
  4. Test for an open circuit in the appropriate buss between the GMLAN terminals of the disconnected harness connector and the DLC. Use the note from item 1 for buss identification.
Did you find and correct the condition?		 Go to Step 9  Go to Step 7 
7 Inspect for poor connections at the harness connector of the non-communicating module. 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 9  Go to Step 8 
8
IMPORTANT: Perform the module setup procedure, if required.
Replace the non-communicating module. Refer to Control Module References Did you complete the replacement?		 Go to Step 9  -
9
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Retrieve DTCs from the module that was not communicating.
Does the scan tool display any DTCs which do not begin with a "U"?		 Go to the Diagnostic System Check - Vehicle in Vehicle DTC Information Go to Step 10 
10 Use the scan tool in order to clear the DTCs.
Did you complete the action?		 Go to Step 11  -
11  Retrieve DTCs from 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 Diagnostic System Check - Vehicle in Vehicle DTC Information Go to Step 12 
12
  1. Attempt to communicate with all the modules on the vehicle.
  2. Continue diagnosing or clearing the DTCs until all the modules have been diagnosed and all the DTCs have been cleared.
Does DTC U2103 set in any module?		 Go to Step 2  System OK
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