B1815 – Wiper Rear Motor Down Relay Coil Circuit Open

The ODBII code B1815 indicates that there is an open circuit in the rear wiper motor down relay coil, which means the relay is not receiving the necessary electrical signal to operate the rear wiper motor in the down position.

The severity of ODBII code B1815 is moderate.

Common Causes For: B1814 Wiper Rear Motor Down Relay Coil Circuit Failure

• Faulty rear wiper motor
• Open circuit in the wiring harness
• Bad relay
• Corroded or loose connectors
• Faulty switch or control module
• Blown fuse

Common misdiagnosis for B1815 Wiper Rear Motor Down Relay Coil Circuit Open

• Faulty rear wiper motor
• Bad wiper switch
• Damaged wiring or connectors
• Faulty body control module (BCM)
• Incorrectly diagnosed electrical short
• Malfunctioning relay
• Issues with the main fuse or power supply

Common Troubleshooting Steps

The OBD-II code B1815 indicates an issue with the rear wiper motor down relay coil circuit, specifically that the circuit is open. Here are some common troubleshooting steps to diagnose and potentially resolve this issue:

• Check the Vehicle’s Manual: Refer to the vehicle’s service manual for specific wiring diagrams and component locations related to the rear wiper motor and relay.
• Visual Inspection:
• Inspect the wiring harness and connectors associated with the rear wiper motor and relay for any signs of damage, corrosion, or loose connections.
• Look for frayed wires, broken connectors, or any other physical damage.
• Test the Relay:
• Locate the rear wiper motor relay in the fuse box or relay panel.
• Remove the relay and test it using a multimeter. Check for continuity between the relay terminals when it is energized.
• If the relay is faulty, replace it with a new one.
• Check the Fuse:
• Inspect the fuse associated with the rear wiper motor circuit. If the fuse is blown, replace it and see if the issue persists.
• Test the Wiper Motor:
• Disconnect the rear wiper motor and test it directly by applying power to it. If the motor does not operate, it may be faulty and require replacement.
• Check for Ground:
• Ensure that the rear wiper motor has a good ground connection. Use a multimeter to check for continuity between the motor ground terminal and the vehicle chassis.
• Inspect the Control Switch:
• Check the rear wiper control switch for proper operation. If the switch is faulty, it may not be sending the correct signal to the relay.
• Scan for Additional Codes:
• Use an OBD-II scanner to check for any additional trouble codes that may provide more context or indicate related issues.
• Perform a Circuit Test:
• Use a multimeter to perform a voltage drop test on the circuit. Check for proper voltage at the relay and motor terminals when the wiper switch is activated.
• Consult Technical Resources:
• If the issue persists, consult technical service bulletins (TSBs) or forums specific to your vehicle make and model for any known issues or fixes related to the B1815 code. 1
• Professional Diagnosis:
• If you are unable to resolve the issue after these steps, consider seeking help from a professional mechanic or automotive technician who can perform more advanced diagnostics. By following these steps, you should be able to identify the cause of the B1815 code and take appropriate action to resolve the issue.