U1577 – Communication Bus Off.

The ODBII code U1577 indicates a communication issue where a module on the vehicle’s communication bus is not responding or is offline, potentially due to a fault in the wiring, connectors, or the module itself.

The severity of ODBII code U1577 is moderate to severe.

Common Causes For: U1576 U1576: “Module Communication Failure”

• Faulty wiring or connectors in the communication bus.
• Malfunctioning control modules.
• Short circuits or open circuits in the communication lines.
• Corrupted software or firmware in the control modules.
• Electrical interference or noise in the communication lines.
• Low battery voltage or power supply issues.
• Faulty or damaged sensors connected to the bus.

Common misdiagnosis for U1577 Communication Bus Off.

• Faulty ABS module
• Defective engine control module (ECM)
• Malfunctioning transmission control module (TCM)
• Wiring issues or shorts in the communication lines
• Bad ground connections
• Faulty body control module (BCM)
• Incorrectly diagnosed sensor failures
• Power supply issues to modules
• Software or firmware issues in control modules
• Intermittent connection problems

Common Troubleshooting Steps

The OBD-II code U1577 indicates a communication issue related to the vehicle’s communication bus, specifically that a module is reporting a “Bus Off” condition. This typically means that a module on the communication network is unable to communicate properly, often due to a fault in the network or a malfunctioning module. 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 trouble codes that may be present. This can provide more context about the issue.
• Inspect Wiring and Connectors: Visually inspect the wiring and connectors associated with the communication bus (CAN bus, LIN bus, etc.). Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors of 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 communication lines. Look for any short circuits or open circuits that could be causing the communication failure.
• Test Modules: If you suspect a specific module is causing the issue, you can test that module. This may involve checking its power and ground connections, as well as its ability to communicate on the bus.
• If possible, swap the suspected module with a known good one to see if the problem persists.
• Inspect for Interference: Check for any aftermarket devices or modifications that may be interfering with the communication bus. This includes alarm systems, stereo systems, or other electronic devices.
• Check Battery and Ground Connections: Ensure that the vehicle’s battery is in good condition and that all ground connections are secure. Poor power supply or grounding can lead to communication issues.
• Scan for Module Updates: Some manufacturers provide software updates for their modules. Check if there are any updates available that may resolve communication issues.
• Perform a Network Test: If you have access to advanced diagnostic tools, perform a network test to check the integrity of the communication bus. This can help identify which module is causing the issue.
• 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 returns.
• Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures related to the U1577 code and the communication bus used in your vehicle.1
• Seek Professional Help: If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with the specific vehicle make and model. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1577 code.