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Circuit/System Testing

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  1. Ignition OFF, disconnect the C4 harness connector at the underhood fuse block.
  2. Connect a test lamp between the harness connector terminal G1 and battery voltage.
  3. Command the horn ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always OFF, test the horn relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
    • If the test lamp is always ON, test the horn relay control circuit for a short to ground. If the circuit tests normal, replace the BCM.
  4. If all circuits/connectors test normal, replace the underhood fuse block.
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