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Circuit/System Testing

IMPORTANT: If more than one module is not communicating use Data Communication Schematics  to determine which module is closest to the DLC. Start diagnostics with that module.
Terminal and connector identifiers will be different depending on the individual module being tested. Use Schematic Reference and Connector End View Reference to determine which connector and terminal to access.
  1. Using the DTC Descriptor and Diagnostic Aids, determine the module that is not communicating that should be tested.
  2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
  3. Test for less than 2 ohms between the module ground circuits and ground.
    • If greater than specified range, test the ground circuit for an open/high resistance.
    4. IMPORTANT: Only the high speed GMLAN modules have a wired serial data wake up circuit. Refer to the module schematics to identify which modules have a wake up circuit. If the module that is not communicating does not have a serial data wake up circuit, proceed to step 5.
  4. Ignition ON, verify that a test lamp illuminates between the high speed GMLAN serial data wake up circuit OR the accessory wake up serial data circuit and ground.
    • If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
  5. Ignition ON, verify that a test lamp illuminates between all B+ circuits and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the appropriate module.
  6. Verify that a test lamp illuminates between all ignition voltage circuits and ground.
    • If the test lamp does not illuminate, test the ignition voltage circuits for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the appropriate module.
  7. Test for less than 1 ohm in the GMLAN serial data circuits between the non-communicating module and the module that displays the DTC.
    • If greater than specified range, test the GMLAN serial data circuits for open/high resistance.
  8. If all circuits test normal, replace the module that is not communicating.
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