Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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 horn. The body control module (BCM) may also apply ground to the horn relay control circuit as described above. The horn will 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 horn is not clear and even, refer to Horn - Poor Tone.

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

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

Horn Switch Circuit Test

1. Disconnect the HORN relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit and ground.

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

3. Verify that a test lamp illuminates between the relay coil B+ circuit and ground.

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

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

5. Disconnect the harness connector at the horn.
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.
8. Connect a 15A fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the horn is activated.

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

9. Connect a test lamp between the relay coil B+ circuit and the relay coil control circuit.
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 relay coil 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 relay coil 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 relay coil B+ circuit and the relay coil control circuit.
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 relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the relay coil 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.
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 F6 at the underhood fuse block and the control circuit terminal B at the horn.

⇒	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.

Horn

1. Ignition OFF, disconnect the harness connector at the horn.
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.

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.