U1856 – Module Communication Failure

The ODBII code U1856 indicates a “Module Communication Failure,” meaning there is a problem with communication between vehicle modules, often due to a wiring issue, a faulty module, or a network problem.

The severity of ODBII code U1856 is moderate.

Common Causes For: U1855 Lost Communication with Body Control Module (BCM)”.

• Faulty wiring or connectors
• Failed control module
• Poor ground connections
• Corroded terminals
• Communication network issues (e.g., CAN bus problems)
• Software glitches or outdated firmware
• Intermittent electrical issues
• Battery or power supply problems

Common misdiagnosis for U1856 U1856: “Module Communication Failure”

• Faulty wiring or connectors
• Defective control modules
• Software issues or updates needed
• Battery or power supply problems
• Grounding issues
• Intermittent communication issues
• Other communication protocol failures

Common Troubleshooting Steps

The OBD-II code U1856 indicates a “Module Communication Failure,” which typically means that there is a problem with communication between the vehicle’s control modules. 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 other trouble codes that may be present. Sometimes, other codes can provide additional context for the communication failure.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the affected modules. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the wiring harnesses that connect the modules, as these can be prone to wear and tear.
• Check Power and Ground:
• Ensure that the affected modules are receiving proper power and ground. Use a multimeter to check voltage and ground continuity at the module connectors.
• If there is no power or ground, trace the wiring back to the source to identify any breaks or shorts.
• Test Communication Lines:
• Use a scan tool to check the communication lines (CAN bus, LIN bus, etc.) for proper operation. You can use a scope or a specialized tool to monitor the data signals.
• Look for any interruptions or noise in the communication lines that could indicate a fault.
• Check for Module Faults:
• If a specific module is suspected to be faulty, you may need to test or replace it. This could involve bench testing the module or swapping it with a known good module if available.
• Inspect for Software Issues:
• Ensure that the vehicle’s software is up to date. Sometimes, communication issues can arise from outdated software or firmware in the modules.
• If necessary, reprogram or update the affected modules using the manufacturer’s recommended procedures.
• Clear Codes and Test Drive:
• After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner 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 U1856 code. Different manufacturers may have unique troubleshooting steps or wiring diagrams.
• 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 can systematically identify and resolve the underlying cause of the U1856 code.