Chevy and GMC Duramax Diesel Forum banner
  • Hey Everyone! Vote for the Site Favourite ROTM winner for the year of 2021 HERE!
1 - 1 of 1 Posts

·
Registered
Joined
·
4,708 Posts
Maybe a little help on your horn:
Horns Malfunction

Diagnostic Instructions



  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
  • Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information






Circuit/System Description

Battery positive voltage is applied at all times to the horn relay coil and horn relay switch. Pressing the horn switch applies ground to the horn relay control circuit. The body control module (BCM) also may apply ground to the horn relay control circuit. When the horn relay control circuit is grounded, the horn relay is energized and battery positive voltage is applied to the horn via the horn control circuit. The horn will sound as long as ground is applied to the horn relay control circuit.

Diagnostic Aids

If diagnosing a Horn - Poor Tone condition, inspect the following:


  • Debris or water in the horn assembly.
  • Proper horn mounting hardware torque. Refer to Fastener Tightening Specifications.
  • Debris in the joint where the horns attach to the vehicle.
Circuit/System Verification



  1. Ignition OFF, connect a test lamp between the HORN fuse test point and ground.
  2. Press and release the horn switch. The test lamp should turn ON and OFF when changing between the commanded states.

    • If the test lamp does not illuminate or remains illuminated at all times, refer to Horn Switch Circuit Test.

  1. Ignition ON, 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 does not illuminate, test the control circuit terminal 18 at the BCM for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

  1. Connect a 10A fused jumper wire between the HORN fused test point and B+. The horns should sound and emit a clear and even tone.

    • If the horn does not sound, refer to Horn Circuit Test.
    • If the sound emitted is not clear and even, refer to Horn - Poor Tone.
Circuit/System Testing

Horn Switch Circuit Test



  1. Ignition OFF, disconnect the harness connector at the horn switch.
  2. Test for less than 1 ohm between the ground circuit terminal B and ground.

    • If greater than the specified range, test the ground circuit for and open/high resistance.

  1. Connect the harness connector at the horn switch.
  2. Disconnect the X4 harness connector at the underhood fuse block.
  3. Connect a test lamp between B+ and the control circuit terminal G1.
  4. 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.

  1. Ignition OFF, connect the harness connector at the underhood fuse block. Disconnect the harness connector at the appropriate horn.
  2. Verify that a test lamp does not illuminate between the control circuit terminal B 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.

  1. If all circuits test normal, replace the underhood fuse block.
Horn Circuit Test



  1. Ignition OFF, disconnect the harness connector at the appropriate horn.
  2. Test for less than 1 ohm between the ground circuit terminal A and ground.

    • If greater than the specified range, test the ground circuit for and open/high resistance.

  1. Connect a test lamp between the control circuit terminal B and ground.
  2. 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 voltage. If the circuit tests normal, replace the underhood fuse block.
    • If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
    • If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the horn.

  1. If all circuit test normal, test or replace the horn.
 
1 - 1 of 1 Posts
Top