B1805: Lamp Turn Signal Rear Output Circuit Short To Ground

Definition

The OBD2 code B1805 indicates a short circuit to ground in the rear turn signal output circuit, which can cause the turn signal to malfunction

Common causes

Damaged wiring or connectors
Shorted turn signal bulb
Faulty turn signal relay
Corroded or loose connections
Faulty body control module (BCM)
Water intrusion in the lighting circuit
Incorrectly installed aftermarket lighting
Grounding issues in the circuit

Common misdiagnoses

Faulty turn signal switch
Defective body control module (BCM)
Damaged wiring or connectors
Shorted or damaged bulbs
Incorrectly installed aftermarket lighting
Grounding issues in the circuit
Faulty relay or fuse related to the turn signal system

Troubleshooting steps

1. Visual Inspection
2. Check the wiring and connectors associated with the rear turn signal circuit for any visible damage, fraying, or corrosion
3. Inspect the turn signal bulbs to ensure they are not burnt out or improperly installed
4. Check for Short Circuits
5. Use a multimeter to check for continuity in the turn signal circuit. Disconnect the battery and the affected circuit, then check for continuity between the signal wire and ground. A reading of zero ohms indicates a short to ground
6. Inspect the wiring harness for pinched or damaged wires that could be causing a short
7. Test the Turn Signal Bulbs
8. Remove the rear turn signal bulbs and test them with a multimeter to ensure they are functioning correctly. Replace any faulty bulbs
9. Inspect the Turn Signal Relay
10. Check the turn signal relay for proper operation. A malfunctioning relay can cause issues in the circuit. Swap it with a known good relay if possible
11. Check the Ground Connections
12. Ensure that all ground connections related to the turn signal circuit are clean, tight, and free of corrosion. A poor ground can cause erratic behavior in the circuit
13. Scan for Additional Codes
14. Use an OBD-II scanner to check for any additional trouble codes that may provide more context or indicate related issues
15. Repair or Replace Damaged Components
16. If any damaged wiring, connectors, or components are found during the inspection, repair or replace them as necessary
17. Clear the Codes
18. After making repairs, clear the trouble codes using an OBD-II scanner and take the vehicle for a test drive to see if the code returns
19. Consult Wiring Diagrams
20. If the issue persists, consult the vehicle’s wiring diagrams to trace the circuit and identify any other potential issues
21. Professional Diagnosis
22. If you are unable to resolve the issue after these steps, consider seeking help from a professional mechanic who can perform more advanced diagnostics. By following these steps, you should be able to identify and resolve the issue causing the B1805 code

Definition

Common causes

Common misdiagnoses

Troubleshooting steps

1. Visual Inspection

2. Check the wiring and connectors associated with the rear turn signal circuit for any visible damage, fraying, or corrosion

3. Inspect the turn signal bulbs to ensure they are not burnt out or improperly installed

4. Check for Short Circuits

5. Use a multimeter to check for continuity in the turn signal circuit. Disconnect the battery and the affected circuit, then check for continuity between the signal wire and ground. A reading of zero ohms indicates a short to ground

6. Inspect the wiring harness for pinched or damaged wires that could be causing a short

7. Test the Turn Signal Bulbs

8. Remove the rear turn signal bulbs and test them with a multimeter to ensure they are functioning correctly. Replace any faulty bulbs

9. Inspect the Turn Signal Relay

10. Check the turn signal relay for proper operation. A malfunctioning relay can cause issues in the circuit. Swap it with a known good relay if possible

11. Check the Ground Connections

12. Ensure that all ground connections related to the turn signal circuit are clean, tight, and free of corrosion. A poor ground can cause erratic behavior in the circuit

13. Scan for Additional Codes

14. Use an OBD-II scanner to check for any additional trouble codes that may provide more context or indicate related issues

15. Repair or Replace Damaged Components

16. If any damaged wiring, connectors, or components are found during the inspection, repair or replace them as necessary

17. Clear the Codes

18. After making repairs, clear the trouble codes using an OBD-II scanner and take the vehicle for a test drive to see if the code returns

19. Consult Wiring Diagrams

20. If the issue persists, consult the vehicle’s wiring diagrams to trace the circuit and identify any other potential issues

21. Professional Diagnosis

22. If you are unable to resolve the issue after these steps, consider seeking help from a professional mechanic who can perform more advanced diagnostics. By following these steps, you should be able to identify and resolve the issue causing the B1805 code