U1805 – Transmission Control Module Communication Error

The ODBII code U1805 indicates a communication error between the Transmission Control Module (TCM) and other control modules in the vehicle, suggesting a possible issue with wiring, connectors, or the TCM itself.

The severity of ODBII code U1805 is moderate to severe.

Common Causes For: U1804 U1804: Data Bus Communication Fault

• Faulty Transmission Control Module (TCM)
• Damaged wiring or connectors
• Poor ground connections
• Faulty Engine Control Module (ECM)
• Communication network issues (CAN bus problems)
• Corroded or loose connectors
• Software issues or outdated firmware
• Electrical interference from other components
• Failed sensors related to transmission operation

Common misdiagnosis for U1805 U1805: Transmission Control Module Communication Error

• Faulty Transmission Control Module (TCM)
• Wiring issues or damaged connectors
• Faulty Engine Control Module (ECM)
• Low transmission fluid levels
• Faulty sensors (e.g., speed sensors)
• Battery or charging system issues
• Corrupted software or firmware in the TCM
• Grounding issues in the electrical system
• Faulty diagnostic tools or incorrect code interpretation
• Issues with the vehicle’s CAN bus system

Common Troubleshooting Steps

The OBD-II code U1805 indicates a communication error between the Transmission Control Module (TCM) and other control modules in the vehicle. 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 additional trouble codes. Sometimes, related codes can provide more context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring harness and connectors related to the TCM. Look for signs of damage, corrosion, or loose connections.
• Ensure that all connectors are securely plugged in and that there are no bent pins.
• Check Power and Ground:
• Verify that the TCM is receiving the correct power supply. Use a multimeter to check the voltage at the TCM connector.
• Check the ground connections to ensure they are clean and secure.
• Inspect the CAN Bus:
• The TCM communicates with other modules via the Controller Area Network (CAN) bus. Check for any issues with the CAN bus wiring, such as shorts or opens.
• Use a scan tool to monitor the CAN bus for communication errors.
• Test the TCM:
• If the wiring and connections are good, the TCM itself may be faulty. If possible, test the TCM in another vehicle or replace it with a known good unit to see if the problem persists.
• Check for Software Updates:
• Sometimes, a software update for the TCM or other control modules can resolve communication issues. Check with the manufacturer for any available updates.
• 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 TCM and communication errors. This can provide additional insights and steps tailored to your vehicle model.
• Professional Diagnosis:
• If the issue persists after performing these steps, consider seeking help from a professional mechanic or dealership, as they may have specialized tools and knowledge to diagnose complex communication issues. By following these steps, you can systematically identify and resolve the underlying cause of the U1805 code.