U2947 – Vehicle Communication Bus Malfunction

The ODBII code U2947 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 U2947 is moderate.

Common Causes For: U2946 U2946: “Vehicle Communication Bus Malfunction”

• Faulty wiring or connectors in the communication bus
• Malfunctioning control modules
• Corroded or damaged connectors
• Short circuits in the communication lines
• Open circuits in the communication lines
• Software issues or bugs in the control modules
• Interference from aftermarket devices or modifications
• Low battery voltage or power supply issues

Common misdiagnosis for U2947 U2947: “Vehicle Communication Bus Malfunction”

• Faulty OBDII connector
• Bad ground connections
• Defective ECM/PCM
• Wiring issues or shorts
• Faulty communication modules (e.g., BCM, ABS)
• Corroded connectors
• Software glitches or updates needed
• Battery or power supply issues
• Faulty sensors
• Intermittent faults in the communication bus

Common Troubleshooting Steps

When dealing with OBD-II code U2947, which indicates a “Vehicle Communication Bus Malfunction,” there are several common troubleshooting steps you can take to diagnose and potentially resolve the issue. Here’s a structured approach:

• 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 the Wiring and Connectors: **Visual Inspection: Look for damaged, frayed, or corroded wiring and connectors related to the communication bus (CAN bus).
• **Connector Integrity: Ensure that all connectors are securely attached and free of corrosion.
• Check the Communication Bus: **CAN Bus Voltage: Use a multimeter to check the voltage levels on the CAN bus wires. Typically, you should see around 2.5V on the CAN High and CAN Low lines when the vehicle is on.
• **Signal Integrity: Use an oscilloscope to check for proper signal waveforms on the CAN bus lines.
• Inspect Modules: **Module Functionality: Check if all modules (ECU, TCM, BCM, etc.) are functioning properly. A malfunctioning module can disrupt communication.
• **Reprogram or Reset Modules: Sometimes, reprogramming or resetting the affected modules can resolve communication issues.
• Check for Short Circuits: Inspect the wiring for any short circuits to ground or between the CAN High and CAN Low wires.
• Test the Battery and Ground Connections: Ensure that the vehicle’s battery is in good condition and that all ground connections are clean and secure. Poor grounding can lead to communication issues.
• Look for Interference: Check for any aftermarket devices or modifications that may interfere with the vehicle’s communication systems.
• Perform a Network Test: If available, use a professional scan tool to perform a network test to identify which module(s) are not communicating properly.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to your vehicle make and model that may address known issues with the communication bus.
• Clear Codes and Test Drive: After performing the above checks and repairs, clear the codes and take the vehicle for a test drive to see if the code returns.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 steps, you should be able to identify and resolve the underlying issue causing the U2947 code.