Horns Always On

Horns Always On

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic procedure.
* Diagnostic Procedure Instructions provides and overview of each diagnostic category.

Diagnostic Fault Information






Circuit/System Description

Battery positive voltage is applied at all times to the horn relay coil and horn relay switch. Pressing the horn switch applies ground to the horn relay control circuit. The body control module (BCM) also may apply ground to the horn relay control circuit. When the horn relay control circuit is grounded, the horn relay is energized and battery positive voltage is applied to the horn via the horn control circuit. The horn will sound as long as ground is applied to the horn relay control circuit.

Diagnostic Aids

A sticking horn pad may cause the horn to be ON at all times.

Circuit/System Verification

1. Press the horn pad. The horn relay should click and the horn should sound as long as the horn pad is pressed.
2. Ignition ON. With a scan tool, command the body control module (BCM) Horn Output. The horn relay should click and the horn should sound while commanded ON and stop sounding when commanded OFF.

Circuit/System Testing

1. Ignition OFF, disconnect the horn relay.
2. Verify that a test lamp does not illuminate when connected between the horn control circuit terminal and ground.

• If the test lamp illuminates, test for a short to voltage on the horn control circuit.

3. Verify that a test lamp does not illuminate when connected between the coil side B+ circuit terminal and the coil control circuit.

• If the test lamp illuminates, test for a short to ground on the coil control circuit. It the circuit tests normal, test or replace the BCM.

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

Component Testing

Relay Test
1. Ignition OFF, disconnect the horn relay.
2. Test for less than 200 ohms of resistance 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. Test for less than 2 ohms of resistance between terminals 30 and 87A.

• If greater than the specified range, replace the relay.

5. Install a 10A fused jumper wire between relay terminals 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance 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. Verification Tests

* Inflatable Restraint Steering Wheel Module Coil Replacement
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
* Control Module References for BCM replacement, setup, and programming Programming and Relearning