U2631 – CAN Bus Communication Fault

The ODBII code U2631 indicates a “CAN Bus Communication Fault,” which means there is a problem with the communication between the vehicle’s control modules over the Controller Area Network (CAN) bus.

The severity of ODBII code U2631 is moderate to high.

Common Causes For: U2630 CAN Communication Bus Off.

• Faulty CAN bus wiring or connectors
• Short circuit in the CAN bus
• Open circuit in the CAN bus
• Faulty control module
• Interference from other electrical components
• Poor ground connections
• Corroded or damaged connectors
• Software issues or bugs in the control module
• Incompatible or malfunctioning aftermarket devices
• Low battery voltage or power supply issues

Common misdiagnosis for U2631 U2631: “CAN Bus Communication Fault”

• Faulty CAN Bus wiring
• Defective ECU (Electronic Control Unit)
• Bad ground connections
• Malfunctioning sensors
• Corrupted software or firmware
• Faulty connectors or terminals
• Interference from aftermarket devices
• Low battery voltage or power supply issues
• Incorrectly configured or incompatible modules
• Physical damage to the CAN Bus network

Common Troubleshooting Steps

The OBD-II code U2631 indicates a “CAN Bus Communication Fault.” This code typically points to issues with the Controller Area Network (CAN) bus, which is responsible for communication between various electronic control units (ECUs) in a vehicle. Here are some common troubleshooting steps to diagnose and resolve the issue:

• Check for Additional Codes: Use an OBD-II scanner to check for any other related trouble codes. This can provide more context about the issue.
• Inspect the Wiring and Connectors: **Visual Inspection: Look for damaged, frayed, or corroded wires and connectors related to the CAN bus.
• **Loose Connections: Ensure that all connectors are securely attached and free of corrosion.
• Test the CAN Bus Voltage: Use a multimeter to check the voltage levels on the CAN High and CAN Low wires. The typical voltage levels should be around 2.5V when the bus is idle.
• If the voltage is outside the expected range, there may be a short or open circuit.
• Check for Short Circuits: Inspect the CAN bus wiring for any shorts to ground or to other wires. This can cause communication issues.
• Examine the ECUs: Identify which ECUs are connected to the CAN bus. If one of them is malfunctioning, it can disrupt communication.
• Disconnect each ECU one at a time to see if the code clears or communication is restored.
• Test the Termination Resistors: Ensure that the CAN bus has the correct termination resistors (typically 120 ohms) at both ends of the bus. A missing or faulty resistor can cause communication issues.
• Check for Interference: Look for sources of electrical interference that could affect the CAN bus communication, such as aftermarket accessories or modifications.
• Scan Tool Communication: Use a professional scan tool to check if it can communicate with all ECUs. If some ECUs are unresponsive, it may indicate a problem with the CAN bus.
• Inspect for Water Damage: Check for signs of water intrusion in connectors or ECUs, which can cause communication faults.
• Perform a Network Test: If available, use a CAN bus analyzer or oscilloscope to monitor the data traffic on the bus. This can help identify issues with specific messages or nodes.1
• Clear Codes and Test Drive: After performing repairs, clear the codes and take the vehicle for a test drive to see if the code returns.1
• Consult Technical Service Bulletins (TSBs): Check for any manufacturer-specific TSBs related to the U2631 code, as there may be known issues or fixes.1
• Seek Professional Help: If the issue persists after performing these steps, consider consulting a professional mechanic or automotive technician with experience in CAN bus systems. By following these troubleshooting steps, you can systematically identify and resolve the underlying cause of the U2631 code.