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 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 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 Connector End Views By Name
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 P13 horn assembly should turn ON and OFF when changing between the commanded states.
• If the P13 horn assembly is always ON or always OFF, refer to Horns or Horn Command Malfunction.
• If the sound emitted from the P13 horn assembly 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 ohm between the ground circuit terminal A 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 B 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 B 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 harness connector at the P13 horn assembly.
2. Test for less than 5 ohm between the ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance
3. Connect the harness connector at the P13 horn assembly.
4. Connect a 15A fused jumper wire between the horn fuse test point and B+, verify the P13 horn assembly sounds.
• If the P13 horn assembly does not sound, test the control circuit terminal 9 X3 at the X50A underhood fuse block for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the P13 horn assembly.
5. Disconnect the X5 harness connector at the K9 BCM.
6. Test for greater than 10V between the control circuit terminal 19 and ground.
• If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the X50A underhood fuse block.
7. Connect a 3A fused jumper wire between the control circuit terminal 19 and ground, verify the P13 horn assembly sounds.
• If the P13 horn assembly does not sound, test the control circuit for a short to voltage. If the circuit tests normal, replace the X50A underhood fuse block.
8. If all circuits test normal, replace the K9 BCM.
Horn - Poor Tone
1. Ignition OFF, disconnect the harness connector at the P13 horn assembly.
2. Test for less than 5 ohm 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 X50A underhood fuse block.
4. Test for less than 1 ohm between the control circuit terminal 9 at the X50A underhood fuse block and the control circuit terminal B at the P12 horn.
• If greater than the specified range, test the control circuit for high resistance.
5. If all circuits test normal, test or replace the P13 horn assembly.
Component Testing
Horn Test
1. Ignition OFF, disconnect the harness connector at the P13 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 P13 horn assembly emits a clear and even tone.
• If the sound emitted is not clear and even, replace the P13 horn assembly.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Steering Wheel Horn Contact Replacement Service and Repair
* Horn Replacement Service and Repair
* Fuse Block Replacement Fuse Block Replacement
* Control Module References Control Module References for BCM replacement, setup and programming