U1274 – Communication Bus Off.

The ODBII code U1274 indicates a communication issue where the vehicle’s communication bus is offline or not functioning properly, preventing data exchange between modules.

The severity of ODBII code U1274 Communication Bus Off is moderate to severe.

Common Causes For: U1273 Communication Bus Off.

• Faulty wiring or connectors in the communication bus.
• Malfunctioning control modules.
• Short circuits or open circuits in the communication lines.
• Corroded or damaged connectors.
• Power supply issues to the control modules.
• Software or firmware issues in the control modules.
• Interference from aftermarket devices or modifications.

Common misdiagnosis for U1274 Communication Bus Off.

• Faulty ECM (Engine Control Module)
• Bad wiring or connectors
• Defective sensors
• Malfunctioning ABS module
• Issues with the body control module (BCM)
• Powertrain control module (PCM) failure
• Battery or charging system problems
• Faulty communication lines or networks
• Incorrectly programmed modules
• Grounding issues

Common Troubleshooting Steps

The OBD-II code U1274 indicates a “Communication Bus Off” condition, which typically means that there is a problem with the communication between the vehicle’s control modules. This can be caused by various issues, including wiring problems, module failures, or issues with the communication bus itself. Here are some common troubleshooting steps to diagnose and resolve the U1274 code:

• 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.
• Inspect Wiring and Connectors: Visually inspect the wiring and connectors related to the communication bus (CAN bus, LIN bus, etc.). Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors on the modules involved in the communication.
• Test the Communication Bus: Use a multimeter or an oscilloscope to check the voltage levels and signal integrity on the communication bus wires. Ensure that the bus is receiving the correct voltage and that the signals are within specifications.
• Check for short circuits or open circuits in the communication lines.
• Check for Module Functionality: Identify the modules that are part of the communication network. If possible, test each module individually to ensure they are functioning correctly.
• If a specific module is suspected to be faulty, consider replacing or reprogramming it.
• Inspect for Ground Issues: Ensure that all ground connections related to the communication bus are secure and free of corrosion. Poor grounding can lead to communication issues.
• Look for Interference: Check for any aftermarket devices or modifications that may interfere with the communication bus. This includes alarms, stereo systems, or other electronic devices.
• Perform a Network Test: Some advanced scan tools can perform a network test to check the integrity of the communication bus. This can help identify which module is not communicating properly.
• Clear Codes and Test Drive: After performing the above checks 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.
• Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures related to the communication bus and the U1274 code. This can provide additional insights and steps tailored to your vehicle.
• 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 automotive electronics and communication systems. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1274 code.