U2751 – Control Module Communication Bus Off.

The ODBII code U2751 indicates a communication issue where a control module is unable to communicate on the vehicle’s communication bus, often due to a fault in the module or wiring.

The severity of ODBII code U2751 is moderate to high.

Common Causes For: U2749 Invalid Data Received from Vehicle Control Module.

• Faulty control module
• Poor electrical connections or wiring issues
• Short circuits in the communication lines
• Corroded connectors
• Faulty or damaged communication bus (CAN bus)
• Software or firmware issues in the control module
• Power supply problems to the control module
• Interference from aftermarket devices or modifications

Common misdiagnosis for U2751 Control Module Communication Bus Off.

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

Common Troubleshooting Steps

The OBD-II code U2751 indicates a communication issue on the control module communication bus, specifically that a module is “off” or not responding. This can be caused by various factors, including wiring issues, module failures, or problems with the communication bus itself. Here are some common troubleshooting steps to diagnose and resolve the U2751 code:

• Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide additional context for the issue.
• Inspect Wiring and Connectors: Visually inspect the wiring and connectors related to the control modules on the communication bus. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the ground connections, as poor grounding can lead to communication issues.
• Check the Control Modules: Identify the control module that is reporting the U2751 code. This may require consulting the vehicle’s service manual.
• If possible, test the control module for proper operation. This may involve checking for power and ground at the module, as well as verifying that it is functioning correctly.
• Test the Communication Bus: Use a multimeter or an oscilloscope to check the communication signals on the bus. Look for proper voltage levels and signal integrity.
• If you have access to a scan tool that can monitor live data, check for communication between modules.
• Check for Short Circuits or Open Circuits: Use a multimeter to check for short circuits or open circuits in the communication lines. This includes checking the CAN (Controller Area Network) bus lines if applicable.
• Inspect for Interference: Look for any aftermarket devices or modifications that may be interfering with the communication bus. This includes alarms, stereo systems, or other electronic devices.
• Reset the Control Modules: Sometimes, simply resetting the control modules can resolve communication issues. This can be done by disconnecting the battery for a few minutes or using a scan tool to clear the codes.
• Update or Reprogram Control Modules: If the control module is not responding due to software issues, check if there are any available updates or reprogramming procedures from the manufacturer.
• Replace Faulty Components: If a specific control module is determined to be faulty after testing, it may need to be replaced. Ensure that any replacement module is compatible with the vehicle.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the U2751 code for your specific vehicle make and model. Manufacturers may have known fixes or recommendations for this issue.1
• Seek Professional Help: If the issue persists after performing the above 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 U2751 code.