U2891 – Vehicle Communication Bus Malfunction

The ODBII code U2891 indicates a malfunction in the vehicle communication bus, which affects the ability of various electronic control units (ECUs) to communicate with each other.

The severity of ODBII code U2891 is moderate.

Common Causes For: U2890 U2890: Control Module Communication Bus Fault

• Faulty wiring or connectors in the communication bus.
• Malfunctioning control modules.
• Poor ground connections.
• Corroded or damaged terminals.
• Interference from aftermarket devices.
• Software issues or bugs in the control modules.
• Low battery voltage or power supply issues.
• Faulty or damaged communication bus (CAN bus) transceiver.

Common misdiagnosis for U2891 U2891: “Vehicle Communication Bus Malfunction”

• Faulty ECM (Engine Control Module)
• Defective BCM (Body Control Module)
• Wiring issues or shorts in the communication bus
• Bad connectors or terminals
• Malfunctioning sensors
• Issues with the CAN (Controller Area Network) system
• Power supply problems to modules
• Software glitches or outdated firmware in modules
• Faulty diagnostic tools or equipment
• Interference from aftermarket accessories or modifications

Common Troubleshooting Steps

The OBD-II code U2891 indicates a “Vehicle Communication Bus Malfunction.” This code typically points to issues with the communication between various modules in the vehicle, often related to the CAN (Controller Area Network) bus system. Here are some common troubleshooting steps to diagnose and resolve this issue:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Other codes may provide more context or indicate which module is having communication issues.
• Inspect the Wiring and Connectors: Visually inspect the wiring harnesses and connectors associated with the CAN bus. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors on the modules that are part of the communication network.
• Check the Modules: Identify the modules that are part of the communication bus (e.g., Engine Control Module, Transmission Control Module, Body Control Module).
• Ensure that all modules are functioning properly. If a specific module is malfunctioning, it may disrupt communication.
• Test the CAN Bus: Use a multimeter or an oscilloscope to test the CAN bus signals. Check for proper voltage levels and signal integrity.
• Look for short circuits or open circuits in the CAN bus wiring.
• Inspect for Interference: Check for any aftermarket devices or modifications that may interfere with the vehicle’s communication systems (e.g., alarms, stereo systems, etc.).
• Check Power and Ground: Ensure that all modules have proper power and ground connections. A weak ground or insufficient power supply can cause communication issues.
• Perform a Network Test: Some advanced scan tools can perform a network test to check the communication between modules. This can help identify which module is not responding.
• Reset the Codes: After performing inspections and repairs, clear the codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs): Check for any manufacturer-specific TSBs related to U2891 or communication issues. There may be known fixes or recalls for your vehicle model.
• Seek Professional Help: If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or dealership for further diagnosis. They may have access to specialized tools and software to pinpoint the problem. By following these steps, you should be able to identify and resolve the underlying issue causing the U2891 code.