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 B+ | 2 | 2 | -- | --
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 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 Malfunction.

⇒ | 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 horns do not turn ON and OFF when changing between the commanded states, refer to Command Malfunction.

### Circuit/System Testing

#### Horn Malfunction

1. Ignition OFF, disconnect the X2 harness connector at the horn switch.
2. Ignition ON, test for less than 1 ohm between the ground circuit terminal 1 and ground.

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

3. Ignition OFF, connect the 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 87 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 85 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 87 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 30 and ground.

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

7. Ignition OFF, disconnect the harness connector at the appropriate horn.
8. Test for less than 5 ohms 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.
10. Ignition ON, connect a 15A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. 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 horns.

11. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
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 appropriate horn.
2. Test for less than 5 ohms 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 HORN relay.
4. Test for less than 1 ohm between the control circuit terminal 87 and the control circuit terminal B at the horn.

⇒ | If greater than the specified range, test the control circuit for high resistance.

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

#### Command Malfunction

1. Ignition OFF, disconnect the HORN relay.
2. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
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 is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp is always OFF, test circuit the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

### Component Testing

#### Horn Test

1. Ignition OFF, disconnect the harness connector at the appropriate 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.

#### 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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Horn Replacement

• | Steering Wheel Horn Switch Replacement

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