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 Relay Control | 1 | 2 | B2750 00 | --
Horn Control | 2 | 2 | 1 | --
Horn Switch Ground | -- | 2 | 2 | --
Horn Ground | -- | 2 | 2 | --
1. Horn Always On 2. Horn Inoperative

### Circuit/System Description

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 horns. The body control module (BCM) may also apply ground to the horn relay control circuit as described above. The horns sound as long as ground is applied to the horn relay control circuit.

### Diagnostic Aids

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:

• | Debris or water in the horn assembly.

• | Proper horn mounting hardware torque. Refer to Fastener Tightening Specifications.

• | Debris in the joint where the horns attach to the vehicle.

• | Debris in direct contact with the horn

• | Vehicle components vibrating while the horn is sounding

### 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 Verification

1. Ignition OFF, connect a test lamp between the HORN fuse test point and ground.
2. Press and release the horn switch. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | If the test lamp does not illuminate or remains illuminated at all times, refer to Horn Switch Circuit Test.

3. Ignition ON, command the horn 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 does not illuminate, test the control circuit terminal 18 at the BCM for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Connect a 15A fused jumper wire between the horn fused test point and B+. The horn should sound and emit a clear and even tone.

⇒ | If the horn does not sound, refer to Horn Circuit Test.

⇒ | If the sound emitted is not clear and even, refer to Horn - Poor Tone.

### Circuit/System Testing

#### Horn Switch Circuit Test

1. Disconnect the X2 harness connector at the underhood fuse block.
2. Connect a test lamp between B+ and the control circuit terminal 27.
3. 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 or a sticking horn switch. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp is always OFF, test the control circuit for a short to voltage, an open high resistance, or a horn switch which is not closing.

4. Ignition OFF, connect the X2 harness connector at the underhood fuse block. Disconnect the harness connector at the horn.
5. Verify that a test lamp does not illuminate between the control circuit terminal B and ground.

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.

6. If all circuits test normal, replace the underhood fuse block.

#### Horn Circuit Test

1. Ignition OFF, disconnect the harness connector at the horn.
2. 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 and open/high resistance.

3. Connect a test lamp between the control circuit terminal B and ground.
4. 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 voltage. If the circuit tests normal, replace the underhood fuse block.

⇒ | If the test lamp is always OFF and the HORN fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

⇒ | If the test lamp is always OFF and the HORN fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the horn.

5. If all circuit test normal, test or replace the horn.

#### Horn - Poor Tone

1. Ignition OFF, disconnect the harness connector at the horn.
2. Test for less than 1 ohm 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 X3 harness connector at the underhood fuse block.
4. Test for less than 1 ohm between the control circuit terminal 7 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.

### Component Testing

#### Horn

1. Ignition OFF, disconnect the harness connector at the horn.
2. Install a 15A fused jumper wire between the control terminal B and 12 volts. Install a jumper wire between the ground 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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Underhood Electrical Center or Junction Block Replacement

• | Horn Replacement

• | Steering Wheel Inflatable Restraint Module Replacement

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