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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 320 (Horns System) >> Diagnostic Information and Procedures >> Horns Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2022 Cadillac CT5. However, it is still accessible from the selected car via links, so may be relevant.

Test 1

  1. Ignition/Vehicle - Off
  2. Disconnect the electrical connector: X1 @ X50A Engine Wiring Harness Junction Block
  3. Connect a 15 A fused jumper wire between control circuit terminal F2 and B+.
  4. Verify the P12A Horn - High Note and P12B Horn-Low Note are Active are Active.
    • If the P12A Horn - High Note and P12B Horn-Low Note are always off and the 15 A fuse is OK. 
    1. Ignition/vehicle OFF, disconnect the harness connector at the P12A Horn - High Note and P12B Horn-Low Note.
    2. Test circuit 29 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found.
    3. Replace the P12A Horn - High Note or P12B Horn-Low Note for an internal fault.
    • If the P12A Horn - High Note and P12B Horn-Low Note are always off and the 15 A fuse is open. 
    1. Ignition/vehicle OFF, disconnect the harness connector at the P12A Horn - High Note and P12B Horn-Low Note.
    2. Test circuit 29 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found.
    3. Replace the P12A Horn - High Note or P12B Horn-Low Note for an internal fault.
    • Go to next step: If the P12A Horn - High Note and P12B Horn-Low Note are Active. 
  5. Connect the electrical connector: X1 @ X50A Engine Wiring Harness Junction Block
  6. Disconnect the electrical connector: X5 @ K9 Body Control Module
  7. Ignition - On / Vehicle - In Service Mode
  8. Connect a 3 A fused jumper wire between control circuit terminal 11 and B+.
  9. Verify the P12A Horn - High Note and P12B Horn-Low Note are Active.
    • If the P12A Horn - High Note and P12B Horn-Low Note are always off and the 3 A fuse is OK. 
    1. Ignition/vehicle OFF, disconnect the harness connector at the X50A Engine Wiring Harness Junction Block.
    2. Test circuit 28 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit or ground connection.
      • Go to next step: If an open/high resistance is not found.
    3. Test circuit 28 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found.
    4. Replace the X50A Engine Wiring Harness Junction Block for an internal fault.
    • If the P12A Horn - High Note and P12B Horn-Low Note are always off and the 3 A fuse is open. 
    1. Ignition/vehicle OFF, disconnect the harness connector at the X50A Engine Wiring Harness Junction Block.
    2. Test circuit 28 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found.
    3. Replace X50A Engine Wiring Harness Junction Block for an internal fault.
    • Go to next step: If the P12A Horn - High Note and P12B Horn-Low Note are Active. 
  10. Replace the K9 Body Control Module.

Test 2

  1. Ignition/Vehicle & All vehicle systems - Off
  2. Disconnect the electrical connector: P12A Horn - High Note or P12B Horn - Low Note
  3. Verify a test lamp illuminates between ground circuit terminal 1 and B+.
    • If the test lamp does not illuminate 
    1. Repair the open/high resistance on circuit 550 or the ground connection.
    • Go to next step: If the test lamp illuminates 
  4. Disconnect the electrical connector: X1 @ X50A Engine Wiring Harness Junction Block
  5. Test for less than 1 ohms between the test points: Control circuit terminal 2 @ Component harness & Control circuit terminal F2 @ Fuse/Junction Block Harness
    • If 1 ohms or greater 
    • Repair the open/high resistance in the circuit.
    • Go to next step: If less than 1 ohms 
  6. Test or replace the component: P12A Horn - High Note or P12B Horn - Low Note

Test 3

  1. Ignition/vehicle OFF, disconnect the connector at the S33 Steering Wheel Horn Contact.
  2. Verify a test lamp illuminates between ground circuit terminal 1 and B+.
    • If the test lamp does not illuminate 
    1. Repair the open/high resistance on circuit 1351 or the ground connection.
    • Go to next step: If the test lamp illuminates 
  3. Ignition/vehicle On.
  4. Verify the P12A Horn - High Note & P12B Horn - Low Note are not Active
    • If Active 
    1. Test the circuit 3287 for a short to ground
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found.
    2. Replace the K9 Body Control Module.
    • Go to next step: If Inactive 
  5. Momentarily install a 3 A fused jumper wire between the signal circuit terminal 2 and ground.
  6. Verify the P12A Horn - High Note & P12B Horn - Low Note are Active
    • If the components do not sound and the 3 A fuse is OK 
    1. Test the circuit 3287 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found.
    2. Replace the K9 Body Control Module.
    • If the components do not sound and the 3 A fuse is open 
    1. Test the circuit 3287 for a short to voltage.
      • If a short to voltage is found, repair the fault on the circuit.
      • Go to next step: If a short to voltage is not found.
    2. Replace the K9 Body Control Module.
    • Go to next step: If the components produces a sound 
  7. Test or replace the S33 Steering Wheel Horn Contact.
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