Horns Malfunction RPO LS4

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 fuse, and the horn control circuit to the horns. The body control module (BCM) may also apply ground to the horn relay control circuit as described above. The horns sound as long as ground is applied to the horn relay control circuit.

If diagnosing a Horn - Poor Tone condition, inspect the following:

Schematic Reference

Horn Schematics

Connector End View Reference

Horn Connector End Views

Description and Operation

Horns System Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition OFF, connect a test lamp between the HORN fuse test point and ground.
2. Press and release the horn switch. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp does not illuminate or remains illuminated at all times, refer to Horn Switch Circuit Test.

3. Ignition ON, command the horn 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 does not illuminate, test the control circuit terminal 4 at the BCM for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Connect a 15A fused jumper wire between the horn fused test point and B+. The horn should sound and emit a clear and even tone.

⇒	If the horn does not sound, refer to Horn Circuit Test.

⇒	If the sound emitted is not clear and even, refer to Horn - Poor Tone.

Horn Switch Circuit Test

1. Disconnect the harness connector C2 at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal K3 and B+.
3. Press and release the horn switch. 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 or a sticking horn switch. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage, an open high resistance, or a horn switch which is not closing.

4. Ignition OFF, connect the harness connector at the underhood fuse block. Disconnect the harness connector at the horn assembly.
5. Verify that a test lamp does not illuminate between the control circuit terminal J3 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.

6. If all circuits test normal, test or replace the underhood fuse block.

Horn Circuit Test

1. Ignition OFF, disconnect the harness connector at the horn assembly.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal A and ground.

⇒	If greater than the specified range, test the ground circuit for and open/high resistance.

3. Connect a test lamp between the control circuit terminal B and ground.
4. Press and release the horn switch. 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 underhood fuse block.

⇒	If the test lamp is always OFF and the HORN fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the underhood fuse block.

⇒	If the test lamp is always OFF and the HORN fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the horn assembly.

5. If all circuit test normal, test or replace the horn assembly.

Horn - Poor Tone

1. Ignition OFF, disconnect the harness connector at the horn assembly.
2. Test for less than 1.0 ohm of resistance between the horn assembly ground circuit terminal A and ground.

⇒	If greater than the specified range, test the ground circuit for a high resistance.

3. Disconnect the harness connector C3 at the underhood fuse block.
4. Test for less than 1.0 ohm of resistance between the control circuit terminal J3 at the underhood fuse block and the control circuit terminal B at the horn assembly.

⇒	If greater than the specified range, test the control circuit for a high resistance.

5. If all circuits test normal, test or replace the horn assembly.

Horn

1. Ignition OFF, disconnect the harness connector at the horn assembly.
2. Install a 15A fused jumper wire between the control circuit terminal B and 12 volts. Install a jumper wire between the ground circuit terminal A and ground. Verify the horn emits a clear and even tone.

⇒	If the sound emitted is not clear and even, replace the horn assembly.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Horns Malfunction RPO L26/L32

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 fuse, and the horn control circuit to the horns. The body control module (BCM) may also apply ground to the horn relay control circuit as described above. The horns sound as long as ground is applied to the horn relay control circuit.

If diagnosing a Horn - Poor Tone condition, inspect the following:

Schematic Reference

Horn Schematics

Connector End View Reference

Horn Connector End Views

Description and Operation

Horns System Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, press and release the steering wheel horn pad. The horn should sound and emit a clear and even tone only when the horn pad is pressed.

⇒	If the horn does not sound when the horn pad is pressed or continues sounding after the horn pad is released, refer to Horn Switch Circuit Test.

⇒	If the sound emitted from the horns is not clear and even, refer to Horn - Poor Tone.

2. Command the horns ON and OFF with the scan tool. The horns should turn ON and OFF when changing between the commanded states.

⇒	If the horns do not turn ON and OFF when changing between the commanded states, refer to Horn Circuit Test.

Horn Switch Circuit Test

1. Ignition OFF, disconnect the HORN relay.
2. Ignition ON, verify that a test lamp does not illuminate between the output circuit terminal M8 and ground.

⇒	If the test lamp illuminates, test the output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal K8 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the output circuit for a short to ground. If the circuit tests normal, test or replace the horn relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal K7 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Ignition OFF, disconnect the harness connector at the horn assembly.
6. Test for less than 1.0 ohm of resistance between the horn ground circuit terminal A and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the horn assembly.
8. Ignition ON, connect a 15A fused jumper wire between the B+ circuit terminal K7 and the output circuit terminal M8. Verify the horns are activated.

⇒	If the horn does not activate, test the output circuit for an open/high resistance. If the circuit tests normal, test or replace the horn assembly.

9. Connect a test lamp between the B+ circuit terminal K8 and the control circuit terminal M7.
10. Press and release the steering wheel horn pad. 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, inspect for a sticking horn switch.

⇒	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, inspect for an open horn switch.

11. If all circuits test normal, test or replace the horn relay.

Horn Circuit Test

1. Ignition OFF, disconnect the horn relay.
2. Connect a test lamp between the B+ circuit terminal K8 and the control circuit terminal M7.
3. Ignition ON, command the horn 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 BCM.

⇒	If the test lamp is always OFF, test circuit the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

Horn - Poor Tone

1. Ignition OFF, disconnect the harness connector at the horn assembly.
2. Test for less than 1.0 ohm of resistance between the horn ground circuit terminal A and ground.

⇒	If greater than the specified range, test the ground circuit for a high resistance.

3. Disconnect the harness connector C3 at the underhood fuse block.
4. Test for less than 1.0 ohm of resistance between the control circuit terminal A2 at the underhood fuse block and the control circuit terminal B at the horn assembly.

⇒	If greater than the specified range, test the control circuit for a high resistance.

5. If all circuits test normal, test or replace the horn assembly.

Horn Test

1. Ignition OFF, disconnect the harness connector at the horn assembly.
2. Install a 15A fused jumper wire between the control circuit terminal B and 12 volts.
3. Install a jumper wire between the ground circuit terminal A and ground. Verify the horn emits a clear and even tone.

⇒	If the sound emitted is not clear and even, replace the horn assembly.

Relay Test

1. Ignition OFF, disconnect the HORN relay.
2. Test for 60-180 ohms of resistance between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.