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Circuit/System Testing

WARNING: This page is about a different car, the 2008 Pontiac Torrent and 2008 Chevrolet Equinox. However, it is still accessible from the selected car via links, so may be relevant.
  1. Using DTC Descriptors  and Diagnostic Aids  above, determine the module that is not communicating.
  2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
    3. IMPORTANT: Only the high speed GMLAN modules have a serial data communication enable circuit OR an 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, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
  4. 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.
  5. Ignition ON, verify that a test lamp illuminates between all battery positive 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. 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.
  7. Use Data Link References to verify the non-communicating module uses low speed GMLAN serial data.
    • If the module is GMLAN high speed only, replace the module.
  8. Test for less than 1 ohm on the low speed GMLAN serial data circuit between the non-communicating module and the module that displays the DTC.
    • If greater than the specified range, 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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