For 1990-2009 cars

### Diagnostic Instructions

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

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit/System Description

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.

### Diagnostic Aids

• | Inspect for any debris or water in the horn assembly.

• | Test the horn mounting hardware for proper torque. Refer to Fastener Tightening Specifications .

• | Inspect for debris in the joint where the horns attach to the vehicle.

### Reference Information

#### Schematic Reference

Horn Schematics

#### Connector End View Reference

Horn Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. Press the horn switch. The horn relay should click and the horn should sound as long as the horn switch is pressed.
2. Turn ON the ignition. With a scan tool, command the BCM Horn Output. The horn relay should click and the horn should sound while commanded ON and stop sounding when commanded OFF.

### Circuit/System Testing

1. Verify the horn mounting hardware is tightened to the proper torque. Refer to Fastener Tightening Specifications .

⇒ | If the mounting hardware is not tightened to the proper torque, retorque the fastener to spec.

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

⇒ | If greater than 1.0 ohm, test the ground circuit for a high resistance.

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

### Component Testing

Install a 15-amp fused jumper wire between the control terminal B and 12 volts. Momentarily install a jumper wire between the ground terminal A and ground. The horn should emit a clear and even tone.

⇒ | If the horn does not emit and clear and even tone, replace the horn assembly.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Horn Replacement