WOMS
B code body Medium severity

B1218 Horn Relay Coil Circuit Short to Vbatt

The OBD2 code B1218 indicates a short circuit in the horn relay coil circuit to the battery voltage (Vbatt), suggesting that the circuit is receiving power continuously, which may prevent the horn from functioning...

Definition

The OBD2 code B1218 indicates a short circuit in the horn relay coil circuit to the battery voltage (Vbatt), suggesting that the circuit is receiving power continuously, which may prevent the horn from functioning properly

Common causes

  • Shorted horn relay coil
  • Damaged wiring or connectors
  • Faulty horn relay
  • Corroded terminals
  • Grounding issues
  • Malfunctioning body control module (BCM)

Common misdiagnoses

  • Faulty horn switch
  • Shorted wiring harness
  • Defective horn
  • Malfunctioning body control module (BCM)
  • Incorrectly installed aftermarket accessories
  • Grounding issues
  • Faulty relay socket or connections

Troubleshooting steps

  1. 1. Verify the Code

    Use an OBD-II scanner to confirm the presence of the B1218 code. Clear the code and see if it returns after a short drive

  2. 2. Inspect the Horn Relay

    Locate the horn relay in the fuse box or relay panel. Check for any visible signs of damage, corrosion, or burnt contacts. If necessary, replace the relay with a known good one to see if the issue persists

  3. 3. Check the Wiring

    Inspect the wiring and connectors associated with the horn relay and the horn itself. Look for frayed wires, shorts, or damaged insulation that could cause a short circuit to battery voltage (Vbatt)

  4. 4. Test the Relay Circuit

    Using a multimeter, test the relay circuit for continuity and proper voltage. Check the voltage at the relay terminals when the horn is activated. Ensure that the relay is receiving the correct voltage and that the ground side is functioning properly

  5. 5. Inspect the Horn

    Check the horn itself for any issues. A malfunctioning horn can sometimes cause a short circuit. Test the horn directly by applying battery voltage to see if it operates correctly

  6. 6. Check for Ground Issues

    Ensure that the ground connections for the horn and relay are secure and free of corrosion. A poor ground can lead to erratic behavior and false codes

  7. 7. Look for Short Circuits

    Use a multimeter to check for shorts between the horn relay circuit and the battery voltage. Disconnect the relay and check for continuity between the relay terminals and ground

  8. 8. Examine the Body Control Module (BCM)

    If all other components check out, the issue may lie within the BCM or the wiring harness leading to it. Inspect for any faults or damage

  9. 9. Consult Wiring Diagrams

    Refer to the vehicle’s wiring diagrams to understand the circuit layout and identify any other components that may be involved in the horn relay circuit

  10. 10. Perform a System Reset

    After repairs, clear the code and perform a system reset. Monitor the system to see if the code returns. If you are unable to resolve the issue after these steps, it may be advisable to consult a professional mechanic or technician for further diagnosis