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Circuit/System Testing

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the X4 harness connector at the underhood fuse block.
  2. Connect a test lamp between the control circuit terminal G1 and B+.
  3. Press and release the horn switch. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to ground or a sticking horn switch. If the circuit tests normal, replace the BCM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage, an open high resistance, or a horn switch which is not closing. If the circuit tests normal, replace the BCM.
  4. If all circuits test normal, replace the underhood fuse block.
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