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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Horn Control Circuit | 1 | 1 | 2 | --
Horn Ground Circuit | -- | 1 | -- | --
Horn Relay Control Circuit | 2 | 1 | -- | --
Horn Switch Ground Circuit | -- | 1 | -- | --
1. Horn inoperative 2. Horn on at all times

### 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.

### Reference Information

#### Schematic Reference

Horn Schematics

#### Connector End View Reference

Horn Connector End Views

#### Description and Operation

Horns System Description and Operation

#### Electrical Information Reference

• | Connector Repairs

• | Wiring Repairs

• | Circuit Testing

• | Testing for Intermittent Conditions and Poor Connections

#### 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 body control module (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. Ignition OFF, disconnect the horn relay. The horn should stop sounding with the relay removed.

⇒ | If the horn continues to sound, repair the short to voltage on the relay switch control circuit.

2. Verify that a test lamp does not illuminate when connected between the horn relay supply voltage circuit and the horn relay control circuit.

⇒ | If the test lamp illuminates, test for a short to ground on the horn relay control circuit. If the circuit/connections test normal, replace the BCM.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Inflatable Restraint Steering Wheel Module Coil Replacement

• | Relay Replacement

• | Control Module References for BCM replacement, setup, and programming