Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | 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 | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Horn Control Circuit | 1 | 1 | 2 | -- |
Horn Relay Control Circuit | B2750, 2 | 1 | B2750, 1 | -- |
Horn Switch Ground Circuit | -- | 1 | 1 | -- |
Horn Ground Circuit | -- | 1 | 1 | -- |
1. Horn inoperative 2. Horn on at all times | ||||
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.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Horns System Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
- Press the horn pad. The horn relay should click and the horn should sound as long as the horn pad is pressed.
- 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
- Ignition OFF, disconnect the horn relay.
- Verify that a test lamp does not illuminate when connected between the horn control circuit terminal and ground.
- Verify that a test lamp does not illuminate when connected between the coil side B+ circuit terminal and the coil control circuit.
- If all circuits test normal, test or replace the horn relay.
| ⇒ | If the test lamp illuminates, test for a short to voltage on the horn 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. |
Component Testing
Relay Test
- Ignition OFF, disconnect the horn relay.
- Test for less than 200 ohms of resistance between terminals 85 and 86.
- Test for infinite resistance between the following terminals:
- Test for less than 2 ohms of resistance between terminals 30 and 87A.
- 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 not within the specified range, replace the relay. |
| • | 30 and 86 |
| • | 30 and 87 |
| • | 30 and 85 |
| • | 85 and 87 |
| ⇒ | If not the specified value, replace the relay. |
| ⇒ | If greater than the specified range, replace the relay. |
| ⇒ | If greater than the specified range, replace the relay. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
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 Control Circuit | 1 | 1 | 2 | -- |
Horn Ground Circuit | -- | 1 | -- | -- |
Horn Relay Control Circuit | 2 | 1 | -- | -- |
Horn Switch Ground Circuit | -- | 1 | -- | -- |
1. Horn inoperative 2. Horn on at all times | ||||
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.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Horns System Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
- Press the horn switch. The horn relay should click and the horn should sound as long as the horn switch is pressed.
- Turn ON the ignition. 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
- Ignition OFF, disconnect the horn relay. The horn should stop sounding with the relay removed.
- Verify that a test lamp does not illuminate when connected between the horn relay supply voltage circuit and the horn relay control circuit.
- If all circuits test normal, test or replace the horn relay.
| ⇒ | If the horn continues to sound, repair the short to voltage on the relay switch control circuit. |
| ⇒ | If the test lamp illuminates, test for a short to ground on the horn relay control circuit. If the circuit/connections test normal, replace the BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
