B1803 – Lamp Turn Signal Rear Output Circuit Open

The ODBII code B1803 indicates that there is an open circuit in the rear turn signal lamp output, meaning the vehicle’s system is not detecting a proper connection or signal from the rear turn signal lamp.

The severity of ODBII code B1803 is generally considered moderate.

Common Causes For: B1802 Lamp Turn Signal Rear Output Circuit Failure

• Open circuit in the wiring
• Faulty turn signal bulb
• Defective turn signal relay
• Poor ground connection
• Damaged connector or terminals
• Faulty body control module (BCM)

Common misdiagnosis for B1803 Lamp Turn Signal Rear Output Circuit Open

• Faulty turn signal bulb
• Bad turn signal switch
• Damaged wiring or connectors
• Faulty body control module (BCM)
• Incorrectly installed or loose bulb socket
• Grounding issues
• Faulty relay
• Corroded terminals

Common Troubleshooting Steps

The OBD-II code B1803 indicates a problem with the rear turn signal output circuit, specifically that there is an open circuit. Here are some common troubleshooting steps to diagnose and resolve this issue:

• Check the Vehicle’s Manual: Refer to the vehicle’s service manual for specific information about the turn signal circuit and wiring diagrams.
• Visual Inspection:
• Inspect the rear turn signal bulbs for any signs of damage or burnout. Replace any faulty bulbs.
• Check the bulb sockets for corrosion or damage.
• Look for any damaged or frayed wiring in the turn signal circuit, especially around the rear lights.
• Test the Bulb:
• Remove the bulb and test it with a multimeter to ensure it is functioning properly.
• If the bulb is good, reinstall it and ensure it is seated correctly in the socket.
• Check the Fuses:
• Locate the fuse box and check for any blown fuses related to the turn signal circuit. Replace any blown fuses.
• Inspect the Wiring Harness:
• Follow the wiring harness from the rear turn signal to the main harness. Look for any signs of wear, damage, or disconnection.
• Ensure all connectors are secure and free of corrosion.
• Test the Turn Signal Switch:
• The turn signal switch on the steering column can sometimes fail. Test the switch for continuity using a multimeter.
• If the switch is faulty, it may need to be replaced.
• Check for Ground Issues:
• Ensure that the ground connection for the rear turn signal is secure and free of corrosion. A poor ground can cause an open 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.
• Perform a Continuity Test:
• Use a multimeter to perform a continuity test on the wiring from the turn signal bulb socket back to the turn signal relay or module. This will help identify any breaks in the circuit.
• Inspect the Turn Signal Relay/Module:
• If all else checks out, the turn signal relay or module may be faulty. Test or replace it as necessary. 1
• Clear the Code:
• After performing repairs, clear the trouble code using an OBD-II scanner and take the vehicle for a test drive to see if the code returns. If you are not comfortable performing these steps or if the issue persists after troubleshooting, it may be best to consult a professional mechanic for further diagnosis and repair.