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 provides system voltage to 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 fuse, and the horn control circuit to the horns. The body control module (BCM) may also apply system voltage to the horn relay control circuit as described above. The horns sound as long as ground is applied to the horn relay control circuit.
The BCM provides the pedestrian alert signal circuit with a 12V signal, when the pedestrian friendly alert switch, located on the end of the turn signal/multifunction stalk, is pressed, the signal is pulled low. The BCM will detect the voltage drop in the signal circuit and if the vehicle is in Drive (D), it will command an 8 cycle horn chirp burst.
Diagnostic Aids
OnStar(C) 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 Hybrid/EV Battery Pack X1
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. Vehicle in Service Mode.
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 horns 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 horns do not turn ON and OFF
Refer to Circuit/System Testing - Horns or Horn Command Malfunction.
• If the sound emitted is not clear and even
Refer to Circuit/System Testing - Horn - Poor Tone.
• If the horns turn ON and OFF and emit a even and clear tone
4. Verify the scan tool Pedestrian Friendly Alert Switch parameter changes between Inactive and Active when pressing the pedestrian friendly alert switch.
• If the parameter does not change
Refer to Circuit/System Testing - Pedestrian Friendly Alert Switch Malfunction.
• If the parameter changes
5. All OK.
Circuit/System Testing
Horn Switch Malfunction
1. Vehicle 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 1 and ground.
• If 10 ohms or greater
1. Vehicle 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. Vehicle in Service Mode.
4. Verify the scan tool Horn Switch parameter is Inactive.
• If not Inactive
1. Vehicle OFF, disconnect the harness connector at the K9 body control module.
2. Test for infinite resistance between the signal circuit terminal 1 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 and the ground circuit terminal 1.
6. Verify the scan tool Horn Switch parameter is Active.
• If not Active
1. Vehicle OFF, disconnect the harness connector at the K9 body control module, Vehicle in Service Mode.
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. Vehicle OFF, disconnect the KR3 horn relay, Vehicle in Service Mode.
2. Verify a test lamp illuminates between the B+ circuit terminal 2 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Vehicle OFF.
2. Test for less than 2 ohms in the B+ circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Vehicle OFF.
2. Test for infinite resistance between the B+ circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance,
3. Disconnect the harness connectors at the P12L horn-left and the P12R horn-right
4. Test for infinite resistance between the control circuit terminal 4 and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If greater than infinite resistance, test or replace the KR3 horn relay.
• If the test lamp illuminates
3. Connect a test lamp between the B+ circuit terminal 2 and the control circuit terminal 5.
4. 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. Vehicle OFF, disconnect the harness connector at the K9 body control module, Vehicle in Service Mode.
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. Vehicle 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. Vehicle 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
5. Verify a test lamp does not illuminate between the control circuit terminal 4 and ground.
• If the test lamp illuminates
Repair the short to voltage on the circuit.
• If the test lamp does not illuminate
6. Vehicle in Service Mode, connect a 15 A fused jumper wire between the B+ circuit terminal 2 and the control circuit terminal 4.
7. Verify the P12L horn-left and the P12R horn-right are activated.
• If the P12L horn-left and the P12R horn-right do not activate
1. Vehicle OFF.
2. Test for less than 2 ohms in the control circuit terminal 4 end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, test or replace the P12L horn-left and the P12R horn-right.
• If the P12L horn-left and the P12R horn-right activates
8. Test or replace the KR3 horn relay.
Horn - Poor Tone
1. Vehicle 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. Vehicle 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. Vehicle OFF, disconnect the KR3 horn relay.
4. Test for less than 2 ohms between the P12 horn control circuit terminal 2 and the KR3 horn relay control circuit terminal 4.
• 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.
Pedestrian Friendly Alert Switch Malfunction
1. Vehicle OFF, disconnect the harness connector at the S78 turn signal/multifunction 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 6 and ground.
• If 10 ohms or greater
1. Vehicle 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. Vehicle in Service Mode.
4. Verify the scan tool Pedestrian Friendly Alert Switch parameter is Inactive
• If not Inactive
1. Vehicle OFF, disconnect the harness connector at the K9 body control module.
2. Test for infinite resistance between the signal circuit terminal 6 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 3 and the ground circuit terminal 6.
6. Verify the scan tool Pedestrian Friendly Alert Switch parameter is Active.
• If not Active
1. Vehicle OFF, disconnect the harness connector at the K9 body control module, Vehicle in Service Mode.
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 S78 turn signal/multifunction switch.
Component Testing
Horn Test
1. Vehicle 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. Vehicle OFF, disconnect the X1 and X2 harness connectors at the S33 horn switch.
2. Test for infinite resistance between the signal terminal 1 and the ground terminal 1 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 and the ground terminal 1 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
Turn Signal/Multifunction Switch Test
1. Vehicle OFF, disconnect the harness connector at the S78 turn signal/multifunction switch.
2. Test for infinite resistance between the signal terminal 3 and the ground terminal 6 with the switch in the open position.
• If less than infinite resistance
Replace the S78 turn signal/multifunction switch.
• If infinite resistance
3. Test for less than 3 ohms between the signal terminal 3 and the ground terminal 6 with the switch in the closed position.
• If 3 ohms or greater
Replace the S78 turn signal/multifunction switch.
• If less than 3 ohms
4. All OK
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)
* Steering Wheel Horn Contact Replacement Service and Repair
* Horn Replacement Service and Repair
* Turn Signal Multifunction Switch Replacement Turn Signal Multifunction Switch Replacement
* Control Module References Programming and Relearning for BCM replacement, programming and setup