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Circuit/System Testing

WARNING: This page is about a different car, the 2007 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.

Horn Switch Circuit Test 

  1. Disconnect the harness connector C2 at the underhood fuse block.
  2. Connect a test lamp between the control circuit terminal 26 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.
  4. Ignition OFF, connect the harness connector at the underhood fuse block. Disconnect the harness connector at the horn assembly.
  5. Verify that a test lamp does not illuminate between the control circuit terminal 9 and ground.
    • If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.
  6. If all circuits test normal, test or replace the underhood fuse block.

Horn - Poor Tone 

  1. Ignition OFF, disconnect the harness connector at the horn assembly.
  2. Test for less than 1.0 ohm of resistance between the horn assembly ground circuit terminal A and ground.
    • If greater than the specified range, test the ground circuit for a high resistance.
  3. Disconnect the harness connector C1 at the underhood fuse block.
  4. Test for less than 1.0 ohm of resistance between the control circuit terminal 9 at the underhood fuse block and the control circuit terminal B at the horn assembly.
    • If greater than the specified range, test the control circuit for a high resistance.
  5. If all circuits test normal, test or replace the horn assembly.
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