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

Definition

The OBD2 code B1820 indicates a short circuit in the rear wiper motor up relay coil circuit, meaning that the circuit is receiving power directly from the battery instead of being controlled properly by the relay

Common causes

Shorted wiring or connectors
Faulty rear wiper motor
Defective relay
Corroded or damaged terminals
Malfunctioning switch
Grounding issues

Common misdiagnoses

Faulty rear wiper motor
Defective wiper switch
Wiring issues or shorts in the harness
Malfunctioning body control module (BCM)
Incorrectly installed or damaged relay
Grounding issues
Faulty fuse or circuit breaker

Troubleshooting steps

1. Visual Inspection
2. Check the wiring and connectors associated with the rear wiper motor and relay for any signs of damage, corrosion, or loose connections
3. Inspect the relay itself for any physical damage
4. Check the Relay
5. Test the rear wiper motor relay by swapping it with a similar relay in the fuse box (if applicable) to see if the problem persists
6. If you have a multimeter, you can also test the relay for continuity and proper operation
7. Inspect the Wiper Motor
8. Disconnect the rear wiper motor and check for any signs of damage or short circuits
9. Measure the resistance of the motor windings to ensure they are within specifications
10. Check for Shorts
11. Use a multimeter to check for continuity between the relay coil circuit and the battery. A short circuit will show continuity where there shouldn't be any
12. Inspect the wiring harness for any pinched or frayed wires that could be causing a short
13. Test the Circuit
14. With the ignition on, use a multimeter to check for voltage at the relay and the wiper motor. Ensure that the voltage is within the expected range
15. If there is no voltage, trace the circuit back to the power source to identify any breaks or issues
16. Check Ground Connections
17. Ensure that the ground connections for the rear wiper motor and relay are clean and secure. A poor ground can cause erratic behavior
18. Scan for Additional Codes
19. Use an OBD-II scanner to check for any other related trouble codes that may provide additional context for the issue
20. Consult Wiring Diagrams
21. Refer to the vehicle’s service manual for wiring diagrams to understand the circuit layout and identify any potential issues
22. Replace Faulty Components
23. If any faulty components are identified (such as the relay, wiper motor, or wiring), replace them as necessary
24. Clear Codes and Test Drive
25. 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. If the issue persists after following these steps, it may be advisable to consult a professional mechanic for further diagnosis

Definition

Common causes

Common misdiagnoses

Troubleshooting steps

1. Visual Inspection

2. Check the wiring and connectors associated with the rear wiper motor and relay for any signs of damage, corrosion, or loose connections

3. Inspect the relay itself for any physical damage

4. Check the Relay

5. Test the rear wiper motor relay by swapping it with a similar relay in the fuse box (if applicable) to see if the problem persists

6. If you have a multimeter, you can also test the relay for continuity and proper operation

7. Inspect the Wiper Motor

8. Disconnect the rear wiper motor and check for any signs of damage or short circuits

9. Measure the resistance of the motor windings to ensure they are within specifications

10. Check for Shorts

11. Use a multimeter to check for continuity between the relay coil circuit and the battery. A short circuit will show continuity where there shouldn't be any

12. Inspect the wiring harness for any pinched or frayed wires that could be causing a short

13. Test the Circuit

14. With the ignition on, use a multimeter to check for voltage at the relay and the wiper motor. Ensure that the voltage is within the expected range

15. If there is no voltage, trace the circuit back to the power source to identify any breaks or issues

16. Check Ground Connections

17. Ensure that the ground connections for the rear wiper motor and relay are clean and secure. A poor ground can cause erratic behavior

18. Scan for Additional Codes

19. Use an OBD-II scanner to check for any other related trouble codes that may provide additional context for the issue

20. Consult Wiring Diagrams

21. Refer to the vehicle’s service manual for wiring diagrams to understand the circuit layout and identify any potential issues

22. Replace Faulty Components

23. If any faulty components are identified (such as the relay, wiper motor, or wiring), replace them as necessary

24. Clear Codes and Test Drive

25. 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. If the issue persists after following these steps, it may be advisable to consult a professional mechanic for further diagnosis