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 Switch Signal | B2501 5A | 2 | 2 | --
Horn Control | 2 | 2 | 1 | --
Horn Switch Ground | -- | 2 | 2 | --
Horn Ground | -- | 2 | 2 | --
1. Horn Always On 2. Horn Inoperative

### Circuit/System Description

The right steering wheel control switch monitors the horn switch signal circuit, when the horn pad is pressed, the right steering wheel control switch detects the drop in the horn switch signal circuit and sends a serial data message to the underhood fuse block which commands the horn to sound.

### Diagnostic Aids

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.

### 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 Relay Status parameter while pressing and releasing the horn pad, the parameter should change from On to Off.

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

2. Command the Horn Test with a scan tool, the horn should sound when commanding the horn.

⇒ | 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. Ignition OFF, disconnect the harness connector at the right steering wheel control switch.
2. Ignition ON, verify the scan tool Horn Relay Status parameter is Off.

⇒ | If not the specified value, replace the right steering wheel control switch.

3. Test for infinite resistance between the signal circuit terminal 2 and the low reference circuit terminal 1.

⇒ | If not the specified value, inspect for a sticking horn switch.

4. Test for less than 2 ohms between the signal circuit terminal 2 and the low reference circuit terminal 1 while pressing the horn switch.

⇒ | If greater than the specified range, replace the horn switch.

5. If all circuits test normal, replace the right steering wheel control switch.

#### 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 2 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 1 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, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

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 ground circuit terminal 2 and ground.

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

3. Disconnect the X1 harness connector at the underhood fuse block.
4. Test for less than 1 ohm between the control circuit terminal 32 at the underhood fuse block and the control circuit terminal 1 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 1 and 12V. Install a jumper wire between the ground terminal 2 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.

• | Steering Wheel Horn Switch Replacement

• | Control Module References for underhood fuse block replacement, setup, and programming