U1671 – Control Module Communication Bus Off.

The ODBII 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.

The severity of ODBII code U1671 is moderate to severe.

Common Causes For: U1670 CAN Communication Bus – Invalid or Missing Message.

• 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 misdiagnosis for U1671 Control Module Communication Bus Off.

• 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

Common Troubleshooting Steps

The OBD-II code U1671 indicates a communication issue on the control module communication bus, specifically that a module is “off” or not communicating properly. Here are some common troubleshooting steps to diagnose and resolve this issue:

• 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.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the control modules. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors for the modules involved in the communication bus.
• Check Power and Ground:
• 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.
• If the module is not receiving power, trace the wiring back to the fuse box and check for blown fuses or damaged wiring.
• Test the Control Module:
• 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.
• If possible, swap the suspected faulty module with a known good one to see if the problem resolves.
• Check for Short Circuits:
• 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.
• Look for any signs of damage or wear that could affect communication.
• Scan Tool Communication:
• 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.
• Check for Interference:
• Sometimes, aftermarket accessories or modifications can interfere with the communication bus. Disconnect any aftermarket devices and see if the code clears.
• Clear Codes and Test Drive:
• 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.
• Consult Technical Service Bulletins (TSBs):
• 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.
• Seek Professional Help:
• 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.