B1804 – Lamp Turn Signal Rear Output Circuit Short To Battery

The ODBII code B1804 indicates a short circuit in the rear turn signal output circuit, causing it to be connected directly to the battery, which can lead to malfunctioning of the turn signal lights.

The severity of ODBII code B1804 is moderate.

Common Causes For: B1803 Lamp Turn Signal Rear Output Circuit Open

• Shorted wiring or connectors
• Faulty turn signal lamp
• Malfunctioning turn signal relay
• Corroded or damaged ground connections
• Faulty body control module (BCM)
• Incorrectly installed or damaged aftermarket lighting
• Water intrusion in the lighting circuit

Common misdiagnosis for B1804 Lamp Turn Signal Rear Output Circuit Short To Battery

• Faulty turn signal switch
• Defective body control module (BCM)
• Shorted wiring harness
• Bad ground connection
• Malfunctioning rear lamp assembly
• Incorrect bulb installation or type
• Corroded connectors or terminals
• Faulty relay or fuse issues

Common Troubleshooting Steps

The OBD-II code B1804 indicates a problem with the rear turn signal lamp circuit, specifically a short to battery. Here are some common troubleshooting steps to diagnose and resolve this issue:

• Visual Inspection:
• Check the rear turn signal lamp and its socket for any signs of damage, corrosion, or loose connections.
• Inspect the wiring harness for frayed wires, broken insulation, or any signs of wear that could cause a short circuit.
• Check the Bulb:
• Remove the rear turn signal bulb and inspect it for any damage. Replace it if necessary.
• Ensure that the bulb is the correct type and is properly seated in the socket.
• Test the Circuit:
• Use a multimeter to check for continuity in the turn signal circuit. Disconnect the battery before performing any tests to avoid shorting.
• Check for voltage at the turn signal socket with the turn signal activated. You should see battery voltage when the signal is on.
• Inspect Ground Connections:
• Ensure that the ground connection for the rear turn signal circuit is secure and free of corrosion. A poor ground can cause erratic behavior.
• Check for Shorts:
• With the multimeter, check for continuity between the turn signal wire and the battery positive terminal. If there is continuity, there is a short somewhere in the circuit.
• Inspect the wiring harness for any areas where the wires may be pinched or rubbing against metal surfaces.
• Examine the Turn Signal Relay:
• If applicable, check the turn signal relay for proper operation. A faulty relay can cause issues in the circuit.
• Scan for Additional 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:
• Based on your findings, repair any damaged wiring or connectors. Replace any faulty components, such as the turn signal bulb, socket, or relay.
• Clear the Code:
• After making repairs, clear the trouble code using an OBD-II scanner and take the vehicle for a test drive to see if the code returns.
• Consult a Professional:
• If the issue persists after performing these steps, it may be necessary to consult a professional mechanic for further diagnosis. By following these steps, you should be able to identify and resolve the issue related to the B1804 code.