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Horns Malfunction

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 Short to Ground Open/High Resistance Short to Voltage Signal Performance
Horn Switch Signal 1 2 2 -
Horn Relay Control B2750 02 B2750 04 B2750 01 -
Horn Control 2 2 1 -
Horn Ground - 2 2 -
1. Horn Always On 2. Horn Inoperative


Circuit/System Description

The body control module (BCM) monitors the horn switch signal circuit, when the horn pad is pressed, the BCM detects the drop in the horn switch signal circuit and provides a ground for the Horn PCB relay within the underhood fuse block. The underhood fuse block will then provide B+ voltage to the horn control circuit, sounding the horns

Diagnostic Aids

A short to ground in the horn relay control circuit or a short to voltage in the horn control circuit will cause the horns to sound continuously until the horns overheat 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 .

• 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

Connector End View Reference

Component Connector End Views

Description and Operation

Horns System Description and Operation

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification


1. Ignition ON, observe the scan tool Horn Switch parameter while pressing and releasing the horn pad. The parameter should change from Inactive to Active.

2. If the value does not change, refer to Horn Switch Malfunction.

3. Command the Horn Relay ON and OFF with the scan tool, the P12 horn should turn ON and OFF when changing between the commanded states.

4. If the P12 horn is always ON or always OFF, refer to Horn Malfunction.

5. If the sound emitted from the P12 horn is not clear and even, refer to Horn - Poor Tone.


Circuit/System Testing


Horn Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the S33 horn switch.

2. Test for less than 5 Ω between the horn switch ground circuit terminal A and ground.

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

4. Ignition ON, verify the scan tool Horn Switch parameter is Inactive.

5. If not the specified value, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the K9 BCM.

6. Fit a 3 A fused jumper wire between the signal circuit terminal B and ground. Verify that the scan tool Horn Switch parameter is Active.

7. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

8. If all circuits test normal, test or replace the S33 horn switch.



Horn Malfunction

1. Ignition OFF, disconnect the X2 harness connector at the X50A underhood fuse block.

2. Connect a test lamp between the control circuit terminal 15 and B+.

3. Ignition ON, command the Horn Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

4. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 BCM.

5. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

6. Ignition OFF, connect the X2 harness connector at the X50A underhood fuse block. Disconnect the harness connector at the P12 horn.

7. Test for less than 5.0 Ω between the ground circuit terminal A and ground

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

9. Connect a test lamp between the control circuit terminal B and ground.

10. Command the Horn Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

11. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the X50A underhood fuse block.

12. 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, test or replace the X50A underhood fuse block.

13. 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 X50A underhood fuse block.

14. If all circuits test normal, test or replace the P12 horn.



Horn - Poor Tone

1. Ignition OFF, disconnect the harness connector at the appropriate P12 horn.

2. Test for less than 1 Ω between the ground circuit terminal A and ground.

3. If greater than the specified range, test the ground circuit for high resistance.

4. Disconnect the X3 harness connector at the X50A underhood fuse block.

5. Test for less than 1 Ω between the control circuit terminal 9 at the X50A underhood fuse block and the control circuit terminal B at the P12 horn.

6. If greater than the specified range, test the control circuit for high resistance.

7. If all circuits test normal, test or replace the P12 horn.


Component Testing


Horn Test

1. Ignition OFF, disconnect the harness connector at the appropriate P12 horn.

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 P12 horn emits a clear and even tone.

3. If the sound emitted is not clear and even, replace the P12 horn.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Steering Wheel Horn Contact Replacement

• Horn Replacement

• Front Compartment Fuse Block Replacement

• Control Module References for BCM replacement, setup, and programming