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Circuit/System Testing

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  1. Ignition OFF, disconnect the necessary harness connector of the module that is not communicating.
  2. Test for less than 1 ohm between the module ground circuits and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
    3. IMPORTANT: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit, and the BCM is the output for these circuits. Refer to the module schematics to identify which modules have these circuits. If the module that is not communicating is the BCM or does not have one of these circuits, proceed to step 4.
  3. Ignition ON, verify that a test lamp illuminates between the serial data communication enable circuit OR the accessory wakeup 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.
  4. Ignition ON, verify that a test lamp illuminates between all B+ circuits and ground.
    • If the test lamp does not illuminate, test the 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 module.
  5. Verify that a test lamp illuminates between all ignition voltage circuits and ground.
    • If the test lamp does not illuminate, test the 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 module.
  6. Test for less than 1 ohm on the GMLAN serial data circuits between the non-communicating module and the module that displays the DTC.
    • If greater than the specified range, test the serial data circuit for open/high resistance.
  7. If all circuits test normal, replace the module that is not communicating.
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