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
The 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 horn
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 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 Sunshade - Left (DH6)
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 ON, observe the scan tool Horn Switch parameter while pressing and releasing the horn pad. The parameter should change from Inactive to Active.
• If the value does not change, refer to Horn Switch Malfunction.
2. Command the Horn Relay ON and OFF with the scan tool, the horn should turn ON and OFF when changing between the commanded states.
• If the horn is always ON or always OFF, refer to Horns or Horn Command Malfunction.
• If the sound emitted from the 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 10 ohms between the ground circuit terminal 2 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Horn Switch parameter is Inactive.
• If not the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the K9 BCM.
4. Install a 3 A fused jumper wire between the signal circuit terminal 1 and ground, verify the scan tool Horn Switch parameter is Active.
• 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.
5. If all circuits test normal, test or replace the S33 horn switch.
Horns or Horn Command Malfunction
1. Ignition OFF, disconnect the X2 harness connector at the X50A fuse block-underhood.
2. Connect a test lamp between the control circuit terminal 25 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.
• 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.
• 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.
4. Ignition OFF, connect the X2 harness connector at the X50A fuse block-underhood. Disconnect the harness connector at the P12 horn assembly.
5. Test for less than 1 ohms between the ground circuit terminal 1 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
6. Connect a test lamp between the control circuit terminal 2 and ground.
7. 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.
• 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.
• 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, replace the X50A fuse block-underhood.
8. 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 ohms between the ground circuit terminal 1 and ground.
• If greater than the specified range, test the ground circuit for high resistance.
3. Disconnect the X1 harness connector at the X50A fuse block-underhood.
4. Test for less than 1 ohms between the control circuit terminal 17 at the X50A fuse block-underhood and the control circuit terminal 2 at the P12 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 P12 horn assembly.
Component Testing
Horn Test
1. Ignition OFF, disconnect the harness connector at the P12 horn.
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.
• If the sound emitted is not clear and even, replace the P12 horn.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Steering Wheel Horn Contact Replacement Service and Repair
* Front Compartment Fuse Block Replacement Front Compartment Fuse Block Replacement
* Horn Replacement Service and Repair
* Control Module References Control Module References for BCM replacement, programming and setup