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 Switch Signal | 1 | 2 | 2 | --
Horn Relay Control | B2750 02 | B2750 04 | B2750 01 | --
Horn Control | 2 | 2 | 1 | --
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. The BCM monitors the horn switch signal circuit and when the horn switch is closed the voltage in the horn switch signal circuit drops. The BCM detects the drop in voltage and applies a ground for the relay coil and energizing the relay. The contacts of the switch side of the horn relay closes ailowing voltage to be supplied to the horn control circuit, sounding the horn.

### 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.

• | 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, observe the scan tool Horn parameter while pressing and releasing the horn pad. The parameter should change from Inactive to Active.

⇒ | If the value does not change, refer to Horn Switch Malfunction.

2. Command the Horn Relay Test ON and OFF with the scan tool. The horn should turn ON and OFF when changing between the commanded states.

⇒ | If the P12 horn does not turn ON and OFF when changing between the commanded states, refer to Horn Malfunction.

⇒ | If the sound emitted from the P12 horn is not clear and even, refer to Horn - Poor Tone.

### Circuit/System Testing

#### Horn Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the S33 horn switch.
2. Ignition ON, verify the scan tool Horn parameter is Inactive.

⇒ | If not the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the K9 BCM.

3. Install a 3A fused jumper wire between the signal circuit terminal 1 and ground, verify the scan tool Horn parameter is Active.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

4. If all circuits test normal, test or replace the S33 horn switch.

#### Horn Malfunction

1. Ignition OFF, disconnect the KR3 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 85 and ground.

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

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. Ignition OFF, disconnect the X1 harness connector at the P12 horn.
6. 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.

7. Connect the harness connector at the P12 horn.
8. Ignition ON, connect a 15A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the P12 horn is activated.

⇒ | If the P12 horn does not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the P12 horn.

9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. Command the Horn Relay 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 K9 BCM.

⇒ | 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 K9 BCM.

11. If all circuits test normal, test or replace the KR3 HORN relay.

#### Horn - Poor Tone

1. Ignition OFF, disconnect the X1 harness connector at the P12 horn.
2. 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 a high resistance.

3. Disconnect the KR3 HORN relay.
4. Test for less than 1 ohm between the control circuit terminal 87 and the control circuit terminal 2 at the P12 horn.

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

5. If all circuits test normal, test or replace the P12 horn.

### Component Testing

#### Horn Test

1. Ignition OFF, disconnect the harness connector at the P12 horn.
2. Install a 15A fused jumper wire between the control terminal 2 and 12V. Install a jumper wire between the ground terminal 1 and ground. Verify the P12 horn emits a clear and even tone.

⇒ | If the sound emitted is not clear and even, replace the P12 horn.

#### Relay Test

1. Ignition OFF, disconnect the KR3 HORN relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒ | If not within the specified range, replace the KR3 HORN 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 KR3 HORN 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 KR3 HORN relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Horn Replacement

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