U2974 – Vehicle Communication Bus Malfunction

The ODBII code U2974 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 U2974 is moderate.

Common Causes For: U2973 Lost Communication with the Steering Angle Sensor.

• Faulty wiring or connectors in the communication bus
• Malfunctioning control modules
• Corroded or damaged connectors
• Short circuits in the wiring
• Open circuits in the communication lines
• Interference from aftermarket devices
• Software issues or bugs in the control modules
• Low battery voltage or power supply issues
• Faulty or damaged sensors connected to the bus
• Grounding issues in the vehicle’s electrical system

Common misdiagnosis for U2974 U2974: “Vehicle Communication Bus Malfunction”

• Faulty OBDII connector
• Bad ground connections
• Defective ECM (Engine Control Module)
• Malfunctioning BCM (Body Control Module)
• Wiring issues or shorts in the communication lines
• Faulty sensors or actuators
• Corrupted software or firmware in control modules
• Battery or power supply issues
• Intermittent connection problems
• Issues with aftermarket accessories or modifications

Common Troubleshooting Steps

The OBD-II code U2974 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 Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. Sometimes, multiple codes can provide more context for the issue.
• Inspect Wiring and Connectors: Visually inspect the wiring 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 for Short Circuits or Open Circuits: Use a multimeter to check for continuity in the CAN bus wiring. Look for any short circuits or open circuits that could disrupt communication.
• Test the Modules: Identify the modules that are part of the communication network (e.g., Engine Control Module, Transmission Control Module, Body Control Module).
• Check if the modules are functioning properly. If a specific module is not responding, it may need to be replaced or reprogrammed.
• Inspect the CAN Bus 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 any aftermarket devices or modifications that may interfere with the vehicle’s communication network. This includes alarm systems, stereo systems, or other electronic devices.
• Perform a Network Scan: Use a professional-grade scan tool to perform a network scan. This can help identify which modules are communicating and which are not.
• Update Software/Firmware: Check if there are any software or firmware updates available for the vehicle’s modules. Sometimes, updating the software can resolve communication issues.
• Clear Codes and Test Drive: After performing the above checks and repairs, clear the trouble codes and take the vehicle for a test drive to see if the code reappears.
• Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures related to the CAN bus and the U2974 code.1
• Seek Professional Help: If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who specializes in automotive electronics. By following these troubleshooting steps, you can systematically identify and resolve the underlying issues causing the U2974 code.