Battery positive voltage is applied at all times to the horn relay coil and horn relay switch. Pressing the horn switch applies ground to the horn relay control circuit. The body control module (BCM) also may apply ground to the horn relay control circuit. When the horn relay control circuit is grounded, the HORN relay is energized and battery positive voltage is applied to the horn via the horn control circuit. The horn will sound as long as ground is applied to the horn relay control circuit.

A short to ground in the horn relay control circuit or a short to voltage in the horn control circuit will cause the horn to sound continuously until the horn overheats 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:

Schematic Reference

Horn Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Horns System Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

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

⇒	If the horns do 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 are not clear and even, refer to Horn - Poor Tone.

2. Command the Horn ON and OFF with the scan tool. The horns 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, replace the BCM.

Horn Switch Circuit Test

1. Ignition OFF, disconnect the X277 harness connector at the horn switch.
2. Test for less than 1 ohm between the ground circuit terminal 2 and ground.

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

3. Connect the X277 harness connector at the horn switch and disconnect the HORN relay.
4. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal C1 and ground

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

5. Verify that a test lamp illuminates between the B+ circuit terminal E1 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 control circuit terminal C1 for a short to ground. If the circuit tests normal, test or replace the HORN relay.

6. Verify that a test lamp illuminates between the B+ circuit terminal E2 and ground.

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

7. Disconnect the harness connector at the horn assembly.
8. Test for less than 1 ohm between the ground circuit terminal A and ground.

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

9. Connect the harness connector at the horn assembly.
10. Connect a 15A fused jumper wire between the B+ circuit terminal E2 and the control circuit terminal C1. Verify the horns are activated.

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

11. Connect a test lamp between the B+ circuit terminal E1 and the control circuit terminal C2.
12. 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.

13. If all circuits test normal, test or replace the HORN relay

Horn - Poor Tone

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

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

3. Disconnect the HORN relay.
4. Test for less than 1.0 ohm between the control circuit terminal C1 at the HORN relay and the control circuit terminal 1 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 terminal 1 and 12V. Install a jumper wire between the ground terminal 2 and ground. Verify the horns emit 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 between terminals 85 and 86.

⇒	If 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 30A fused jumper wire between relay terminal 85 and 12V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.