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
Battery positive voltage is applied at all times to the horn relay coil and the horn relay switch. Pressing the horn switch applies ground through the switch contacts and the horn relay control circuit to the coil side of the relay, energizing the relay. Battery voltage is then applied through the switch side of the relay, the horn circuit fuse, and the horn control circuit to the horns. The horns sound as long as ground is applied to the horn relay control circuit.
Diagnostic Aids
OnStar(R) RemoteLink(TM) applications or "apps" downloads are available to owners of certain mobile devices. Unwanted or inadvertent horn activations have been associated with these applications to which the customer may be unaware. Contact the GM Technical Assistance Center regarding information on a remedy for this situation.
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 Fuel Pump and Level Sensor Assembly
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.
2. Verify the scan tool Horn Switch parameter changes between Active and Inactive when pressing and releasing the horn pad.
• If the parameter does not change
Refer to Circuit/System Testing - Horn Switch Malfunction.
• If the parameter changes
3. Verify the P12A Horn-High Note and the P12B Horn-Low Note turns ON and OFF and emit a clear and even tone when commanding the Horn Relay On and OFF with a scan tool.
• If the P12A Horn-High Note and the P12B Horn-Low Note do not turn ON and OFF
Refer to Circuit/System Testing - Horns or Horn Command Malfunction.
• If a single P12 Horn does not turn ON and OFF
Refer to Circuit/System Testing - Single Horn Malfunction.
• If the sound emitted is not clear and even
Refer to Circuit/System Testing - Single Horn Malfunction.
• If the P12A Horn-High Note and the P12B Horn-Low Note turn ON and OFF and emit a even and clear tone
4. All OK.
Circuit/System Testing
Horn Switch Malfunction
1. Ignition OFF and all vehicle systems OFF, disconnect the X1 and X2 harness connectors at the S33 Horn Switch. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the ground circuit terminal A X2 and ground.
• If 10 ohms or greater
1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
3. Ignition ON.
4. Verify the scan tool Horn Switch parameter is Inactive.
• If not Inactive
1. Ignition OFF, disconnect the harness connector at the K9 Body Control Module.
2. Test for infinite resistance between the signal circuit terminal 1 X1 and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the K9 Body Control Module.
• If Inactive
5. Install a 3 A fused jumper wire between the signal circuit terminal 1 X1 and the ground circuit terminal A X2.
6. Verify the scan tool Horn Switch parameter is Active.
• If not Active
1. Ignition OFF, disconnect the harness connector at the K9 Body Control Module, ignition ON.
2. Test for less than 1 V between the signal circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V
3. Test for less than 2 ohms in the signal circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K9 Body Control Module.
• If Active
7. 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+, ignition ON.
3. Verify the test lamp turns ON and OFF when commanding the Horn Relay On and Off with a scan tool.
• If the test lamp is always OFF
1. Ignition OFF, disconnect the harness connector at the K9 Body Control Module, ignition ON.
2. Test for less than 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V
3. Ignition OFF.
4. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K9 Body Control Module.
• If the test lamp is always ON
1. Ignition OFF, disconnect the harness connector at the K9 Body Control Module.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the K9 Body Control Module.
• If the test lamp turns ON and OFF
4. Ignition OFF, connect the X2 harness connector at the X50A Fuse Block-Underhood. Disconnect the harness connector at the P12A Horn-High Note and the P12B Horn-Low Note.
5. Connect a test lamp between the control circuit terminal 2 and ground.
6. Verify the test lamp turns ON and OFF when commanding the Horn Relay On and Off with a scan tool.
• If the test lamp is always OFF and the circuit fuse is good
1. Ignition OFF, disconnect the harness connector at the X50A Fuse Block-Underhood.
2. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the X50A Fuse Block-Underhood.
• If the test lamp is always OFF and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, test or replace the P12 Horn.
• If the test lamp is always ON
1. Ignition OFF, disconnect the harness connector at the X50A Fuse Block-Underhood, ignition ON.
2. Test for less than 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the X50A Fuse Block-Underhood.
• If the test lamp turns ON and OFF
7. Test or replace the P12A Horn-High Note and the P12B Horn-Low Note.
Horn - Poor Tone
1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the appropriate P12 Horn. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the ground circuit terminal 1 and ground.
• If 10 ohms or greater
1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the high resistance in the circuit.
• If less than 2 ohms, repair high resistance in the ground connection.
• If less than 10 ohms
3. Ignition OFF, disconnect the X1 harness connector at the X50A Fuse Block-Underhood.
4. Test for less than 2 ohms between the P12 Horn control circuit terminal 2 and the X50A Fuse Block-Underhood control circuit terminal 11 X1.
• If 2 ohms or greater
Repair the high resistance in the control circuit.
• If less than 2 ohms
5. 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 2 and 12 V. Install a jumper wire between the ground terminal 1 and ground.
3. Verify the P12 horn turns ON and OFF
• If the P12 Horn does not turn ON and OFF
Replace the P12 horn.
• If the P12 Horn turns ON and OFF
4. All OK
Horn Switch
1. Ignition OFF, disconnect the X1 and X2 harness connectors at the S33 Horn Switch.
2. Test for infinite resistance between the signal terminal 1 X1 and the ground terminal A X2 with the switch in the open position.
• If less than infinite resistance
Replace the S33 Horn Switch.
• If infinite resistance
3. Test for less than 3 ohms between the signal terminal 1 X1 and the ground terminal A X2 with the switch in the closed position.
• If 3 ohms or greater
Replace the S33 Horn Switch.
• If less than 3 ohms
4. All OK
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair
* Steering Wheel Horn Contact Replacement Service and Repair
* Horn Replacement Service and Repair
* Front Compartment Fuse Block Replacement Front Compartment Fuse Block Replacement
* Control Module References Control Module References for BCM replacement, programming and setup