U1971 – Vehicle Communication Bus Malfunction

The ODBII code U1971: Vehicle Communication Bus Malfunction indicates a failure in the communication network between various control modules in the vehicle, which may affect their ability to exchange data properly.

The severity of ODBII code **U1971: Vehicle Communication Bus Malfunction** is generally considered moderate to severe.

Common Causes For: U1968: Module Communication Failure

• Faulty wiring or connectors in the communication bus.
• Malfunctioning control modules.
• Corroded or damaged connectors.
• Short circuits or open circuits in the communication lines.
• Interference from aftermarket devices.
• Software issues or bugs in the control modules.
• Low battery voltage or poor power supply to modules.
• Faulty or incompatible OBD-II scanner.

Common misdiagnosis for U1971: 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
• Incorrectly installed aftermarket accessories
• Software glitches or outdated firmware in modules
• Battery or power supply issues
• Interference from other electronic devices

Common Troubleshooting Steps

The OBD-II code **U1971: Vehicle Communication Bus Malfunction** indicates a problem with the communication between various control modules in the vehicle. This can be due to issues with the wiring, connectors, or the modules themselves. 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. Sometimes, related codes can provide more context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring harnesses and connectors associated with the communication 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:
• Use a multimeter to check for short circuits in the wiring. Ensure that the communication lines are not shorted to ground or to each other.
• Test the Modules:
• If possible, test the individual control modules (e.g., ECM, BCM, ABS, etc.) for proper operation. A malfunctioning module can disrupt communication.
• If you have access to a scan tool that can communicate with each module, check if they respond correctly.
• Inspect the Communication Bus:
• Check the integrity of the communication bus (CAN bus, LIN bus, etc.). Use an oscilloscope or a specialized scan tool to monitor the bus signals for proper voltage levels and signal integrity.
• Check for Interference:
• Look for any aftermarket devices or modifications that may interfere with the vehicle’s communication systems. This includes alarms, remote starters, or other electronic devices.
• Battery and Ground Connections:
• Ensure that the vehicle’s battery is in good condition and that all ground connections are clean and secure. Poor power or ground can lead to communication issues.
• Software Updates:
• Check if there are any available software updates for the vehicle’s control modules. Sometimes, manufacturers release updates to fix communication issues.
• Clear Codes and Test Drive:
• After performing any repairs or adjustments, clear the trouble codes and take the vehicle for a test drive to see if the code returns.
• Consult Service Manual:
• Refer to the vehicle’s service manual for specific diagnostic procedures related to the communication bus and any manufacturer-specific troubleshooting steps. 1
• Professional Diagnosis:
• If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with advanced diagnostic tools. By following these steps, you should be able to identify and resolve the underlying cause of the U1971 code.