U2787 – Vehicle Communication Bus Malfunction

The ODBII code U2787: Vehicle Communication Bus Malfunction indicates a problem with the communication between various control modules in the vehicle, suggesting that they are unable to exchange data properly.

The severity of ODBII code U2787 is moderate.

Common Causes For: U2785 U2785: “Vehicle Communication Bus Malfunction”

• Faulty wiring or connectors in the communication bus
• Malfunctioning control modules
• Corrupted software or firmware in control modules
• Poor ground connections
• Interference from aftermarket devices
• Damaged or shorted communication lines
• Low battery voltage or power supply issues
• Faulty or damaged OBD-II port

Common misdiagnosis for U2787 U2787: Vehicle Communication Bus Malfunction

• Faulty ECM (Engine Control Module)
• Defective BCM (Body Control Module)
• Wiring issues or shorts in the communication lines
• Bad ground connections
• Malfunctioning sensors or actuators
• Issues with the CAN bus system
• Faulty diagnostic connectors
• Software or firmware issues in control modules

Common Troubleshooting Steps

The OBD-II code U2787 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. Addressing related codes can help in diagnosing the root cause.
• Inspect Wiring and Connectors: **Visual Inspection: Check the wiring and connectors associated with the CAN bus for any signs of damage, corrosion, or loose connections.
• **Repair or Replace: Repair any damaged wires or connectors and ensure all connections are secure.
• Test the CAN Bus: **Multimeter Testing: 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 idle.
• **Scope Testing: If available, use an oscilloscope to analyze the CAN bus signals for proper communication patterns.
• Check for Short Circuits: Inspect the CAN bus wiring for any short circuits to ground or to other wires. This can cause communication failures.
• Inspect Modules: **Module Functionality: Check the functionality of the modules connected to the CAN bus. A malfunctioning module can disrupt communication.
• **Reprogram or Replace: If a specific module is identified as faulty, it may need to be reprogrammed or replaced.
• Check for Interference: Look for any aftermarket devices or modifications that may interfere with the CAN bus communication, such as alarms, stereo systems, 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 grounding can lead to communication issues.
• Clear Codes and Test Drive: After performing repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code reappears.
• Consult Technical Service Bulletins (TSBs): Check for any manufacturer-specific TSBs related to the U2787 code or communication issues for your vehicle make and model.
• Professional Diagnosis: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing CAN bus issues. By following these steps, you should be able to identify and resolve the underlying cause of the U2787 code.