U1812 – refers to a communication issue between the transmission control module (TCM) and the engine control module (ECM).

The ODBII code U1812 indicates a communication issue between the Transmission Control Module (TCM) and the Engine Control Module (ECM), suggesting a failure in data exchange between these two components.

The severity of ODBII code U1812 is typically moderate to high.

Common Causes For: U1811 refers to a communication issue between the transmission control module (TCM) and the engine control module (ECM).

• Faulty wiring or connectors between TCM and ECM
• Failed TCM or ECM
• Corroded or damaged connectors
• Poor ground connections
• Software issues or incompatibility
• Low battery voltage or weak battery
• Faulty transmission sensors
• Interference from aftermarket accessories or modifications

Common misdiagnosis for U1812 refers to a communication issue between the transmission control module (TCM) and the engine control module (ECM).

• Faulty TCM
• Faulty ECM
• Wiring issues
• Corroded connectors
• Faulty sensors (e.g., speed sensors)
• Transmission fluid issues
• Battery or charging system problems
• Software glitches or updates needed
• Grounding issues
• Other communication errors (e.g., CAN bus issues)

Common Troubleshooting Steps

When dealing with OBD-II code U1812, which indicates a communication issue between the Transmission Control Module (TCM) and the Engine Control Module (ECM), there are several common troubleshooting steps you can follow:

• Check for Other Codes: Start by scanning the vehicle for any other diagnostic trouble codes (DTCs). Sometimes, multiple codes can provide additional context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring harness and connectors between the TCM and ECM for any signs of damage, corrosion, or loose connections.
• Ensure that all connectors are securely plugged in and that there are no bent pins.
• Check for Short Circuits or Open Circuits:
• Use a multimeter to check for continuity in the wiring between the TCM and ECM. Look for any short circuits or open circuits that could be causing communication issues.
• Inspect Ground Connections:
• Ensure that the ground connections for both the TCM and ECM are secure and free of corrosion. Poor ground connections can lead to communication problems.
• Test the TCM and ECM:
• If possible, test the TCM and ECM to ensure they are functioning correctly. This may involve using specialized diagnostic equipment or swapping in known good modules if available.
• Check for Software Updates:
• Verify if there are any software updates available for the TCM or ECM. Sometimes, manufacturers release updates to address communication issues.
• Inspect the CAN Bus:
• If your vehicle uses a Controller Area Network (CAN) for communication, check the CAN bus for proper operation. Look for any faults in the bus that could affect communication between modules.
• Clear Codes and Test Drive:
• After performing the above checks and repairs, clear the codes using a scan tool and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs):
• Check for any TSBs related to the U1812 code for your specific vehicle make and model. Manufacturers may have specific recommendations or known issues that can help in troubleshooting.
• Professional Diagnosis:
• If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing communication issues. By following these steps, you can systematically identify and resolve the communication issue indicated by the U1812 code.