U1838 – Module Communication Failure

The ODBII code U1838 indicates a “Module Communication Failure,” meaning there is a problem with communication between the vehicle’s control modules, often due to a wiring issue, a faulty module, or a network problem.

The severity of ODBII code U1838 is moderate.

Common Causes For: U1835 U1835: “Control Module Communication Failure”

• Faulty wiring or connectors
• Malfunctioning control module
• Poor ground connections
• Corrupted software or firmware
• Intermittent electrical issues
• Communication network failure (e.g., CAN bus issues)
• Low battery voltage or power supply issues
• Damaged or shorted circuits

Common misdiagnosis for U1838 U1838: “Module Communication Failure”

• Faulty wiring or connectors
• Defective control module
• Software issues or updates needed
• Power supply problems
• Grounding issues
• Intermittent communication issues
• Other communication protocol failures

Common Troubleshooting Steps

The OBD-II code U1838 indicates a “Module Communication Failure,” which typically means that there is a problem with communication between various modules in the vehicle’s network. 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, multiple codes can provide more context for the issue.
• 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 the Modules:
• If possible, test the affected modules individually to ensure they are functioning correctly. This may involve using specialized diagnostic tools or swapping with known good modules.
• Some modules may have self-diagnostic capabilities that can provide additional information.
• Inspect the CAN Bus:
• The communication between modules often occurs over a Controller Area Network (CAN) bus. Check for any issues with the CAN bus wiring, such as shorts, opens, or interference.
• Use an oscilloscope or a CAN bus diagnostic tool to monitor the bus signals for proper communication.
• Check for Software Updates:
• Sometimes, communication issues can be resolved with a software update. Check with the vehicle manufacturer for any available updates for the affected modules.
• 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 Technical Service Bulletins (TSBs):
• Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common communication issues.
• 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 and its electronic systems. By following these troubleshooting steps, you can systematically identify and resolve the underlying cause of the U1838 code.