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
--- | --- | --- | --- | ---
Relay Coil B+ | 1 | 1 | -- | --
Relay Switch B+ | 1 | 1 | -- | --
Relay Control | 2 | 1 | -- | --
Horn Control | 1 | 1 | 2 | --
Horn Switch Ground | -- | 1 | -- | --
Horn Ground | -- | 1 | -- | --
1. Horn Inoperative 2. Horn Always On

### Circuit/System Description

The horn is controlled by the horn relay through a high side drive control circuit. When the relay is energized battery voltage will be supplied to the horn through the horn control circuit. The horn relay is controlled by the horn switch through a low side drive control circuit. Battery voltage is supplied to the relay coil at all times and when the horn switch is pressed the relay control circuit is grounded and the relay will be energized.

### Reference Information

#### Schematic Reference

Horn Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Horns System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the horn relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

3. Verify that a test lamp illuminates between the B+ circuit terminal 86 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 horn control circuit terminal 87 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 30 and ground.

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

5. Disconnect the harness connector at the horn.
6. Test for less than 10 ohms between the horn ground circuit terminal 1 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 B+ circuit terminal 30 and the horn control circuit terminal 87. Verify the horn is activated.

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

9. Disconnect the harness connector at the horn switch.
10. Test for less than 10 ohms between the switch ground circuit terminal and ground

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

11. Connect the harness connector at the horn switch.
12. Connect a test lamp between the B+ circuit terminal 86 and the relay control circuit terminal 85.
13. 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. If the circuit tests normal, replace the 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, replace the horn switch.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Horn Replacement