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 Views)
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 (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Command the Horn Relay ON and OFF with the scan tool, the P12 horns should turn ON and OFF when changing between the commanded states.
• If the P12 horns are always ON or always OFF, refer to Horns or Horn Command Malfunction.
• If the sound emitted from the P12 horns are not clear and even, refer to Horn - Poor Tone.
2. Command the P12 horns ON and OFF by pressing and releasing the horn pad. The P12 horns should turn ON with each press of the horn pad.
• If horns are always OFF, refer to Horn Switch Malfunction.
Circuit/System Testing
Horns or Horn Command 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 20 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 underhood fuse block. Disconnect the harness connector at the appropriate P12 horn.
5. Test for less than 1 ohm between the ground circuit terminal B 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 A 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 underhood fuse block.
• 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 underhood fuse block.
8. 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 ohm between the ground circuit terminal B and ground.
• If greater than the specified range, test the ground circuit for high resistance.
3. Disconnect the X1 harness connector at the X50A underhood fuse block.
4. Test for less than 1 ohm between the control circuit terminal 32 at the X50A underhood fuse block and the control circuit terminal A 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 P12 horn.
Horn Switch Malfunction
1. Ignition OFF, disconnect the X2 harness connector at the S33 horn switch.
2. Test for less than 30 ohm between the ground circuit terminal 1 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Disconnect the X1 harness connector at the S33 horn switch.
4. Ignition ON, test for greater than 10V between the signal circuit terminal 1 and ground.
• 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 BCM.
5. 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 appropriate P12 horn.
2. Install a 15 A fused jumper wire between the control terminal A and 12 V. Install a jumper wire between the ground terminal B 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 diagnostic procedure.
* Steering Wheel Horn Contact Replacement (Service and Repair)
* Horn Replacement (Service and Repair)
* Accessory Wiring Junction Block Retainer Replacement (Removal and Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup and programming