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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 has overviews of all diagnostic categories.


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 Assembly Control

2

2

1

-

Horn Assembly Ground

-

2

2

-

Horn Switch 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 Printed Circuit Board (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 information on diagnostic tools

Circuit/System Verification


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

2. If the P12 Horn is always ON or always OFF, refer to Horns or Horn Command Malfunction.

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

4. Command the P12 Horn ON and OFF by pressing and releasing the horn pad. The P12 Horn should turn ON and OFF when changing between the commanded states.

5. If horns are always OFF, refer to Horn Switch Malfunction.


Circuit/System Testing


Horns or Horn Command Malfunction

1. Ignition ON, disconnect X2 from the harness connector at the X50A Fuse Block - Underhood.

2. Connect a test lamp between the X2 harness connector control circuit terminal 25 and B+.

3. Ignition ON, command the P12 to Horn 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 Body Control Module.

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 Body Control Module.

6. With the ignition OFF connect X2 harness connector to X50A, body electronic module at P12 horn assembly.

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

10. Ignition ON, command the P12 Horn 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 Fuse Block - Underhood.

12. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the X50A Fuse Block - Underhood.

13. If all circuits test normal, test or replace the P12 Horn assembly.



Horn - Poor Tone

1. Ignition OFF, disconnect the harness connector at the P12 Horn assembly.

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

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

4. Disconnect the X1 harness connector from the X50A Fuse Block - Underhood.

5. Test for less than 1 Ω between the control circuit terminal 17 at the X50A Fuse Block - Underhood and the control circuit terminal 2 at the P12 Horn assembly.

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 assembly.



Horn Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the S33 Horn Switch.

2. Test for less than 30 Ω between the 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, test for greater than 10 V between the signal circuit terminal B and ground.

5. If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module.

6. If all circuits test normal, test or replace the S33 Horn Switch.


Component Testing


Horn Test

1. Ignition OFF, disconnect the harness connector at the P12 Horn assembly.

2. Install a 15 A fused jumper wire between the control terminal 2 and 12 V. Install a jumper wire between the ground terminal 1 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 assembly.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Steering Wheel Horn Switch Replacement

• Horn Replacement

• Underhood Electrical Center or Junction Block Replacement

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