U1671: Control Module Communication Bus Off

Definition

The OBD2 code U1671 indicates a communication issue where a control module is unable to communicate over the vehicle's communication bus, often due to a fault in the module or wiring

Common causes

Faulty control module
Damaged wiring or connectors
Poor ground connections
Communication bus short circuit
Open circuit in the communication bus
Faulty or disconnected sensors
Interference from aftermarket devices
Software issues or programming errors

Common misdiagnoses

Faulty control module
Wiring issues
Poor ground connections
Faulty sensors
Corrupted software/firmware
Battery or power supply problems
Intermittent connection issues
Other communication bus errors

Troubleshooting steps

1. Check for Other Codes

Start by scanning the vehicle for any other diagnostic trouble codes (DTCs). Other codes may provide additional context or indicate which module is having communication issues
2. Inspect Wiring and Connectors
3. Visually inspect the wiring and connectors associated with the control modules. Look for signs of damage, corrosion, or loose connections
4. Pay special attention to the connectors for the modules involved in the communication bus
5. Check Power and Ground
6. Ensure that the affected control module has proper power and ground. Use a multimeter to check voltage at the module's power supply pins and ground continuity
7. If the module is not receiving power, trace the wiring back to the fuse box and check for blown fuses or damaged wiring
8. Test the Control Module
9. If the module is suspected to be faulty, you may need to test it. This can involve checking for proper operation, ensuring it responds to commands, and verifying that it communicates with other modules
10. If possible, swap the suspected faulty module with a known good one to see if the problem resolves
11. Check for Short Circuits
12. Inspect the communication lines (CAN bus) for any short circuits or opens. Use a multimeter to check for continuity and resistance in the communication wires
13. Look for any signs of damage or wear that could affect communication
14. Scan Tool Communication
15. Use a professional scan tool to check if you can communicate with the affected module. If you cannot communicate with it, this may indicate a problem with the module itself or the communication bus
16. Check for Interference
17. Sometimes, aftermarket accessories or modifications can interfere with the communication bus. Disconnect any aftermarket devices and see if the code clears
18. Clear Codes and Test Drive
19. After performing the above checks and repairs, clear the codes using a scan tool and take the vehicle for a test drive to see if the code returns
20. Consult Technical Service Bulletins (TSBs)
21. Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to communication bus problems
22. Seek Professional Help
23. If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with the specific vehicle and its systems. By following these steps, you should be able to identify and resolve the underlying issue causing the U1671 code

Definition

Common causes

Common misdiagnoses

Troubleshooting steps

1. Check for Other Codes

2. Inspect Wiring and Connectors

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

4. Pay special attention to the connectors for the modules involved in the communication bus

5. Check Power and Ground

6. Ensure that the affected control module has proper power and ground. Use a multimeter to check voltage at the module's power supply pins and ground continuity

7. If the module is not receiving power, trace the wiring back to the fuse box and check for blown fuses or damaged wiring

8. Test the Control Module

9. If the module is suspected to be faulty, you may need to test it. This can involve checking for proper operation, ensuring it responds to commands, and verifying that it communicates with other modules

10. If possible, swap the suspected faulty module with a known good one to see if the problem resolves

11. Check for Short Circuits

12. Inspect the communication lines (CAN bus) for any short circuits or opens. Use a multimeter to check for continuity and resistance in the communication wires

13. Look for any signs of damage or wear that could affect communication

14. Scan Tool Communication

15. Use a professional scan tool to check if you can communicate with the affected module. If you cannot communicate with it, this may indicate a problem with the module itself or the communication bus

16. Check for Interference

17. Sometimes, aftermarket accessories or modifications can interfere with the communication bus. Disconnect any aftermarket devices and see if the code clears

18. Clear Codes and Test Drive

19. After performing the above checks and repairs, clear the codes using a scan tool and take the vehicle for a test drive to see if the code returns

20. Consult Technical Service Bulletins (TSBs)

21. Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to communication bus problems

22. Seek Professional Help

23. If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with the specific vehicle and its systems. By following these steps, you should be able to identify and resolve the underlying issue causing the U1671 code