WOMS
B code body Medium severity

B1821 Wiper Rear Motor Up Relay Coil Circuit Short To Ground

The OBD2 code B1821 indicates a short circuit to ground in the rear wiper motor up relay coil circuit, which can prevent the rear wiper from functioning properly

Definition

The OBD2 code B1821 indicates a short circuit to ground in the rear wiper motor up relay coil circuit, which can prevent the rear wiper from functioning properly

Common causes

  • Damaged wiring or connectors
  • Short circuit in the relay coil circuit
  • Faulty rear wiper motor
  • Defective relay
  • Corroded or loose connections
  • Water intrusion or moisture in the circuit
  • Faulty body control module (BCM)

Common misdiagnoses

  • Faulty rear wiper motor
  • Damaged wiring or connectors
  • Faulty wiper switch
  • Malfunctioning body control module (BCM)
  • Incorrectly installed or defective relay
  • Grounding issues in the electrical system
  • Short circuits in the wiring harness

Troubleshooting steps

  1. 1. Visual Inspection

    Wiring and Connectors: Inspect the wiring harness and connectors related to the rear wiper motor and relay. Look for any signs of damage, fraying, corrosion, or loose connections

  2. 2. Relay Condition

    Check the rear wiper relay for any physical damage or signs of overheating

  3. 3. Check the Relay

    Test the Relay: Remove the relay and test it using a multimeter. You can also swap it with a similar relay (if available) to see if the problem persists

  4. 4. Relay Socket

    Inspect the relay socket for corrosion or damage

  5. 5. Inspect the Wiper Motor

    Motor Condition: Check the rear wiper motor for any signs of damage or wear. If the motor is faulty, it may cause a short circuit

  6. 6. Ground Connection

    Ensure that the ground connection for the wiper motor is secure and free of corrosion

  7. 7. Check for Shorts

    Continuity Test: Use a multimeter to check for continuity in the wiring between the relay and the wiper motor. Look for any shorts to ground in the circuit

  8. 8. Isolate the Circuit

    Disconnect the wiper motor and relay, then check the wiring harness for shorts to ground

  9. 9. Inspect the Fuse

    Fuse Check: Check the fuse associated with the rear wiper system. If the fuse is blown, it may indicate a short circuit somewhere in the system

  10. 10. Scan for Additional Codes

    Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes that may provide more context to the issue

  11. 11. Repair or Replace Components

    Repair Wiring: If you find damaged wiring or connectors, repair or replace them as necessary

  12. 12. Replace Faulty Components

    If the relay or wiper motor is found to be faulty, replace them

  13. 13. Clear Codes and Test

    Clear the Code: After making repairs, clear the trouble codes using an OBD-II scanner

  14. 14. Test the System

    Operate the rear wiper to ensure it functions correctly and that the code does not return

  15. 15. Consult a Professional

    If the issue persists after performing these steps, it may be best to consult a professional mechanic for further diagnosis and repair. By following these steps, you should be able to identify and resolve the issue related to the B1821 code