U0039: Vehicle Communication Bus B (+) Open

Definition

The OBD2 code U0039 indicates that there is an open circuit or a communication issue in the Vehicle Communication Bus B (+) circuit, which can affect data transmission between various control modules in the vehicle

Common causes

Damaged wiring or connectors
Faulty control module
Poor ground connection
Short circuit in the communication bus
Corroded terminals
Disconnected or loose connectors
Faulty or damaged sensors on the bus
Interference from aftermarket devices

Common misdiagnoses

Faulty OBDII connector
Bad ground connections
Defective ECM/PCM
Wiring harness issues
Faulty communication modules
Battery or power supply problems
Corroded connectors
Software issues or updates needed
Faulty sensors or actuators
Incorrectly installed aftermarket accessories

Troubleshooting steps

1. Check for Additional Codes

Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context about the issue
2. Inspect Wiring and Connectors
3. Visually inspect the wiring and connectors associated with the communication bus. Look for signs of damage, corrosion, or loose connections
4. Pay special attention to the connectors at the modules that are part of Bus B
5. Test the Voltage and Ground
6. Use a multimeter to check for proper voltage and ground at the communication bus terminals. Ensure that the voltage levels are within the manufacturer's specifications
7. Check for continuity in the wiring to ensure there are no breaks in the circuit
8. Check for Short Circuits
9. Inspect the wiring for any short circuits to ground or to other circuits that could affect the communication bus
10. Use a multimeter to test for continuity between the Bus B wires and ground
11. Inspect Modules
12. Identify the modules that are connected to Bus B and check for any signs of failure or malfunction
13. If possible, test the modules individually to ensure they are functioning correctly
14. Check for Interference
15. Look for any aftermarket devices or modifications that may interfere with the communication bus. This includes alarms, stereo systems, or other electronic devices
16. Clear Codes and Test Drive
17. After performing inspections and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns
18. Refer to the vehicle's service manual for specific wiring diagrams and troubleshooting procedures related to the communication bus
19. Professional Diagnosis
20. If the issue persists after performing the above steps, consider seeking help from a professional mechanic or automotive technician who has experience with vehicle communication systems. By following these steps, you should be able to identify and resolve the issue related to the U0039 code

Definition

Common causes

Common misdiagnoses

Troubleshooting steps

1. Check for Additional Codes

2. Inspect Wiring and Connectors

3. Visually inspect the wiring and connectors associated with the communication bus. Look for signs of damage, corrosion, or loose connections

4. Pay special attention to the connectors at the modules that are part of Bus B

5. Test the Voltage and Ground

6. Use a multimeter to check for proper voltage and ground at the communication bus terminals. Ensure that the voltage levels are within the manufacturer's specifications

7. Check for continuity in the wiring to ensure there are no breaks in the circuit

8. Check for Short Circuits

9. Inspect the wiring for any short circuits to ground or to other circuits that could affect the communication bus

10. Use a multimeter to test for continuity between the Bus B wires and ground

11. Inspect Modules

12. Identify the modules that are connected to Bus B and check for any signs of failure or malfunction

13. If possible, test the modules individually to ensure they are functioning correctly

14. Check for Interference

15. Look for any aftermarket devices or modifications that may interfere with the communication bus. This includes alarms, stereo systems, or other electronic devices

16. Clear Codes and Test Drive

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

18. Refer to the vehicle's service manual for specific wiring diagrams and troubleshooting procedures related to the communication bus

19. Professional Diagnosis

20. If the issue persists after performing the above steps, consider seeking help from a professional mechanic or automotive technician who has experience with vehicle communication systems. By following these steps, you should be able to identify and resolve the issue related to the U0039 code