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Circuit/System Testing

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  1. Using the DTC Descriptor and Diagnostic Aids above, 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. IMPORTANT: Only the high speed GMLAN modules have a the serial data communication enable circuit OR the accessory wakeup serial data circuit. Refer to the module schematics to identify which modules have these circuits. If the module that is not communicating 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, repair 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 battery positive voltage circuits and ground.
    • If the test lamp does not illuminate, repair 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 faulty module.
  5. Verify that a test lamp illuminates between all ignition voltage circuits and ground.
    • If the test lamp does not illuminate, repair 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 faulty module.
  6. Test for less than 1 ohm of resistance between the module ground circuits and ground.
    • If greater than 1 ohm, repair the ground circuit for an open.
  7. Use Data Link References to determine if the non-communicating module should use low speed GMLAN serial data.
    • If the module is GMLAN high speed only, replace the module.
  8. Test for less than 1 ohm of resistance in the low speed GMLAN serial data circuit between the non-communicating module and the module that displays the DTC.
    • If greater than 1 ohm of resistance, test the low speed GMLAN serial data circuit for open/high resistance.
  9. If all circuits test normal, replace the module that is not communicating.
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