B1821 – Wiper Rear Motor Up Relay Coil Circuit Short To Ground

The ODBII 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.

The severity of ODBII code B1821 is moderate.

Common Causes For: B1820 Wiper Rear Motor Up Relay Coil Circuit Short To Battery

• 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 misdiagnosis for B1821 Wiper Rear Motor Up Relay Coil Circuit Short To Ground

• 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

Common Troubleshooting Steps

The OBD-II code B1821 indicates a problem with the rear wiper motor up relay coil circuit, specifically a short to ground. Here are some common troubleshooting steps to diagnose and resolve this issue:

• 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.
• **Relay Condition: Check the rear wiper relay for any physical damage or signs of overheating.
• 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.
• **Relay Socket: Inspect the relay socket for corrosion or damage.
• 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.
• **Ground Connection: Ensure that the ground connection for the wiper motor is secure and free of corrosion.
• 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.
• **Isolate the Circuit: Disconnect the wiper motor and relay, then check the wiring harness for shorts to ground.
• 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.
• 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.
• Repair or Replace Components: **Repair Wiring: If you find damaged wiring or connectors, repair or replace them as necessary.
• **Replace Faulty Components: If the relay or wiper motor is found to be faulty, replace them.
• Clear Codes and Test: **Clear the Code: After making repairs, clear the trouble codes using an OBD-II scanner.
• **Test the System: Operate the rear wiper to ensure it functions correctly and that the code does not return.
• 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.