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Home >> GMC >> 2002 >> Jimmy 2D Utility, Part Time, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 1083 (Data Link Communication System) >> Diagnostic Information and Procedures >> DTC U1000 and U1255: Class 2 Data Link Malfunction/Lost Communications >> Test Description

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. 1:  A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
  2. 2:  The modules which are not communicating are the likely cause of U1000 or U1255 being set. The following modules communicate on the class 2 serial data circuit:
    • BCM
    • EBCM
    • ECM
    • HUD
    • HVAC Control Module (CJ2)
    • IPC
    • MSM (A43)
    • PCM
    • Radio
    • SDM
    • TCM
    • Theft Deterrent Control Module
    • VIU (UG1)
    • Devices on the Auxiliary Power Drop Connector
  3. 5:  The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
  4. 6:  The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
  5. 7:  The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
  6. 11:  The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
  7. 13:  If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
  8. 14:  The module which set U1000 or U1255 is the likely cause of the malfunction.
DTC U1000 and U1255

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 record any DTCs in the range of U1001-U1254 with a history status? Go to DTC U1001-U1254  Go to Step 2 
2 
  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to communicate with each module on the class 2 serial data circuit. If using a Tech 2, obtain this information using the class 2 Message Monitor feature.
  3. Record all of the modules communicating on the class 2 serial data circuit.
  4. Compare the list of modules which are communicating to the list given.
Do any modules on the class 2 serial data circuit not communicate?		 Go to Step 3  Go to Step 13 
3 Test the battery positive voltage circuits and the ignition voltage circuits of the module that is not communicating for an open or short to ground. Refer to Control Module References in Body Control System for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 9  Go to Step 4 
4
  1. Turn OFF the ignition.
  2. Test the ground circuits of the module that is not communicating for an open. Refer to Control Module References in Body Control System for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 9  Go to Step 5 
5 
  1. Disconnect the star connector.
  2. Inspect for poor connection at the star connector. 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 6 
6  Test the class 2 serial data circuit of the module that is not communicating for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 9  Go to Step 7 
7  Inspect for poor connections at the battery positive voltage circuits, the ignition voltage circuits, the ground circuits, and the class 2 serial data circuit of the module that is not communicating. 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 Replace the module which is not communicating. Refer to Control Module References in Body Control System for the appropriate repair instructions.
Did you complete the replacement?		 Go to Step 11  -
9
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Select the Display DTCs function for the module which was not communicating.
Does the scan tool display and DTCs which do not begin with a "U"?		 Go to Control Module References in Body Control System for the applicable Diagnostic System Check 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  Select the Display DTCs function for the modules which had U1000 or U1255 set as a current DTC.
Does the scan tool display DTCs which do not begin with a "U"?		 Go to Control Module References in Body Control System for the applicable Diagnostic System Check Go to Step 12 
12 Use the scan tool in order to clear the DTCs.
Did you complete the action?		 System OK -
13  Did you record any other DTCs for the modules which had U1000 or U1255 set as a current DTC? Go to Control Module References in Body Control System for the applicable Diagnostic System Check Go to Step 14 
14 
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Use the scan tool in order to clear the DTCs.
  4. Turn OFF the ignition for at least 5 seconds.
  5. Turn ON the ignition, with the engine OFF.
  6. Select the Display DTCs function.
Does the scan tool display U1000 or U1255 set as a current DTC?		 Go to Step 15  Go to Diagnostic Aids
15 Replace the module which had U1000 or U1255 set as a current DTC. Refer to Control Module References in Body Control System for the appropriate repair instructions.
Did you complete the replacement?		 System OK -
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