• | 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. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Horn Relay Control | 1 | 2 | 2 | -- |
Horn Control | 2 | 2 | 1 | -- |
Horn Switch Ground | -- | 2 | 2 | -- |
Horn Ground | -- | 2 | 2 | -- |
1. Horn Always On 2. Horn Inoperative |
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.
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. |
Horns System Description and Operation
⇒ | If the test lamp does not illuminate or remains illuminated at all times, refer to Horn Switch Circuit Test. |
⇒ | If the test lamp does not illuminate, test the control circuit terminal 18 at the BCM harness connector C5 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
⇒ | 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. |
⇒ | If greater than the specified range, test the ground circuit for and open/high resistance. |
⇒ | If the test lamp is always ON, test the control circuit for a short to ground or a sticking horn pad/switch. If the circuit tests normal, replace the BCM. |
⇒ | If the test lamp is always OFF, test the control circuit for a short to voltage, an open high resistance, or a horn switch which is not closing. |
⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block. |
⇒ | If greater than the specified range, test the ground circuit for and open/high resistance. |
⇒ | 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 and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the underhood fuse block. |
⇒ | If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the horn. |
⇒ | If greater than the specified range, test the ground circuit for a high resistance. |
⇒ | If greater than the specified range, test the control circuit for a high resistance. |
⇒ | If the sound emitted is not clear and even, test or replace the horn. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for BCM replacement, setup and programming |