Horns Malfunction
Horns Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions 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 the horn relay switch. Pressing the horn switch applies ground through the switch contacts and the horn relay control circuit to the coil side of the relay, energizing the relay. Battery voltage is then applied through the switch side of the relay, the HORN fuse, and the horn control circuit to the horns. The body control module (BCM) may also apply ground to the horn relay control circuit as described above. The horns sound as long as ground is applied to the horn relay control circuit.
Diagnostic Aids
OnStar(R) RemoteLink(TM) applications or "apps" downloads are available to owners of certain mobile devices. Unwanted or inadvertent horn activations have been associated with these applications to which the customer may be unaware. Contact the GM Technical Assistance Center regarding information on a remedy for this situation.
A short to ground in the horn relay control circuit or a short to voltage in the horn control circuit will cause the horn to sound continuously until the horn overheats and become inoperative.
Rotate the steering wheel while pressing the horn pad to identify intermittent and poor connections within the steering column.
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 Specifications.
* Debris in the joint where the horns attach to the vehicle.
* Debris in direct contact with the horn
* Vehicle components vibrating while the horn is sounding
Reference Information
Schematic Reference
Horn Schematics Electrical Diagrams
Connector End View Reference
Component Connector End Views A/C Compressor Clutch
Description and Operation
Horns System Description and Operation Description and Operation
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
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.
3. Connect a 15 A fused jumper wire between the horn fuse test point and B+. The horns should sound and emit a clear and even tone.
• If the horns do 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 ohms between the ground circuit terminal B and ground.
• If greater than the specified range, test the ground circuit for and open/high resistance.
3. Connect the harness connector at the horn switch.
4. Disconnect the X2 harness connector at the underhood fuse block.
5. Connect a test lamp between B+ and the control circuit terminal K3.
6. 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.
7. Ignition OFF, connect the X2 harness connector at the underhood fuse block. Disconnect the harness connector at the horn assembly.
8. 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.
9. If all circuits test normal, replace the underhood fuse block.
Horn Circuit Test
1. Ignition OFF, disconnect the harness connector at the horn assembly.
2. Test for less than 1 ohms between the ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for and open/high resistance.
3. Connect a test lamp between the control circuit terminal B and ground.
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 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 assembly.
5. If all circuit test normal, test or replace the horn assembly.
Horn - Poor Tone
1. Ignition OFF, disconnect the harness connector at the horn assembly.
2. Test for less than 1 ohms between the ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for high resistance.
3. Disconnect the X3 harness connector at the underhood fuse block.
4. Test for less than 1 ohms between the control circuit terminal J3 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 high resistance.
5. If all circuits test normal, test or replace the horn assembly.
Component Testing
Horn
1. Ignition OFF, disconnect the harness connector at the horn assembly.
2. Install a 15 A fused jumper wire between the control terminal B and 12 V. Install a jumper wire between the ground terminal A and ground. Verify the horn emits a clear and even tone.
• If the sound emitted is not clear and even, replace the horn assembly.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Horn Replacement Service and Repair
* Steering Wheel Horn Switch Replacement Service and Repair
* Instrument Panel Electrical Center or Junction Block Replacement - Right Side (Impala) Instrument Panel Electrical Center or Junction Block Replacement - Right Side (Impala)
* Control Module References Control Module References for BCM replacement, programming and setup