The diagnostic trouble code (DTC) U1073 in Mitsubishi vehicles indicates a problem with the Controller Area Network (CAN) bus communication, specifically a “bus off” condition within the ETACS-ECU (Electronic Time and Alarm Control System). This article outlines the causes, symptoms, and diagnostic procedures for troubleshooting the U1073 Mitsubishi code.
A “bus off” condition occurs when the ETACS-ECU detects an excessive number of errors on the CAN bus, causing it to shut down communication to protect the network. This can lead to various malfunctions in systems controlled by the ETACS, such as lighting, power windows, and central locking. The U1073 code is typically logged when the ETACS-ECU loses and then resumes communication after the ignition is cycled.
Common Causes of U1073 Mitsubishi
The most common causes of the U1073 code include:
- Wiring Harness Issues: Damaged, corroded, loose, or poorly connected wiring harnesses and connectors within the CAN bus system can disrupt communication and trigger the error. This includes terminals pushed back into the connector housing.
- Faulty ETACS-ECU: In some cases, a malfunctioning ETACS-ECU itself can be the root cause of the communication breakdown.
Diagnosing U1073 Mitsubishi: A Step-by-Step Guide
Resolving the U1073 code involves a systematic diagnostic process:
Step 1: CAN Bus Diagnostics with M.U.T.-III
Utilize the Mitsubishi Multi-Use Tester III (M.U.T.-III) to perform a comprehensive diagnosis of the CAN bus lines. This specialized diagnostic tool can pinpoint communication errors and identify faulty components. If the M.U.T-III indicates a problem with the CAN bus, repair the identified issue according to the manufacturer’s specifications (Refer to GROUP 54C – Troubleshooting).
Step 2: Verify DTC Reset After CAN Bus Repair
After addressing any CAN bus issues:
- Clear the U1073 DTC from the ETACS-ECU memory using the M.U.T.-III.
- Cycle the ignition from the “OFF” (LOCK) position to the “ON” position.
- Check if the U1073 code reappears.
If the code persists, proceed to the next step. If the code is not present, the problem may have been an intermittent issue, such as a loose connection. Refer to GROUP 00 – How to Cope with Intermittent Malfunctions for further guidance on troubleshooting these issues.
Step 3: ETACS-ECU Replacement and ID Code Registration
If the U1073 code returns after clearing and cycling the ignition:
- Replace the ETACS-ECU with a new unit.
- Register the ID codes for the new ETACS-ECU using the M.U.T.-III. Refer to the appropriate documentation for ID code registration procedures.
Step 4: Final DTC Verification
After replacing the ETACS-ECU:
- Clear the DTCs once again.
- Cycle the ignition.
- Verify that the U1073 code is no longer present.
Conclusion
The U1073 Mitsubishi diagnostic trouble code signifies a critical communication breakdown within the vehicle’s CAN bus system. By following this comprehensive diagnostic procedure, technicians can accurately identify the root cause, whether it be wiring harness issues or a faulty ETACS-ECU, and implement the necessary repairs to restore proper communication and vehicle functionality. Always consult the appropriate Mitsubishi service manual for detailed wiring diagrams and specific repair instructions.
