U1870 – refers to a communication issue between the transmission control module (TCM) and other control modules in the vehicle.

The ODBII code U1870 indicates a communication issue between the transmission control module (TCM) and other control modules in the vehicle, suggesting a failure in data exchange or signal integrity.

The severity of ODBII code U1870 is generally considered moderate to high.

Common Causes For: U1869 U1869: “Module Communication Line Fault”

• Faulty Transmission Control Module (TCM)
• Damaged wiring or connectors
• Poor ground connections
• Faulty Engine Control Module (ECM)
• Corrupted software or firmware
• Short circuits in the communication lines
• Intermittent electrical connections
• Issues with the vehicle’s CAN bus system
• Low battery voltage or power supply issues
• Faulty sensors affecting communication

Common misdiagnosis for U1870 refers to a communication issue between the transmission control module (TCM) and other control modules in the vehicle.

• Faulty Transmission Control Module (TCM)
• Wiring or connector issues
• Faulty Engine Control Module (ECM)
• Incorrectly diagnosed transmission problems
• Faulty sensors (e.g., speed sensors)
• Battery or charging system issues
• Software or firmware issues in control modules
• Grounding issues in the electrical system

Common Troubleshooting Steps

The OBD-II code U1870 indicates a communication issue between the Transmission Control Module (TCM) and other control modules in the vehicle. This can lead to various performance issues, including erratic shifting or failure of the transmission to operate correctly. Here are some common troubleshooting steps to diagnose and resolve the issue:

• Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. Codes related to other modules can provide additional context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring harness and connectors associated with the TCM and other related modules for any signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors for bent pins or poor contact.
• Check Power and Ground:
• Verify that the TCM is receiving the correct power supply and ground. Use a multimeter to check voltage at the TCM connector.
• Ensure that the ground connections are clean and secure.
• Test Communication Lines:
• Use a scan tool to check the communication lines (CAN bus) for proper operation. You can use a scope to check for signal integrity on the CAN bus.
• Look for any short circuits or open circuits in the communication lines.
• Inspect Other Control Modules:
• Check other control modules that communicate with the TCM for any issues. A malfunctioning module can disrupt communication.
• Ensure that all modules are functioning correctly and that their connections are secure.
• Update Software/Firmware:
• Check if there are any software updates available for the TCM or other related modules. Sometimes, communication issues can be resolved with a software update.
• Perform a Hard Reset:
• Disconnect the vehicle’s battery for a few minutes to reset the modules. Reconnect and see if the code reappears.
• Check for Interference:
• Look for any aftermarket devices or modifications that may interfere with the vehicle’s communication network.
• Consult Technical Service Bulletins (TSBs):
• Check for any TSBs related to the U1870 code for your specific vehicle make and model. Manufacturers may have specific recommendations or known issues.
• Replace the TCM:
• If all other steps fail and the TCM is suspected to be faulty, consider replacing it. Ensure that the replacement module is compatible with your vehicle. 1
• Professional Diagnosis:
• If you are unable to resolve the issue, consider seeking help from a professional mechanic or dealership with experience in diagnosing communication issues. By following these steps, you should be able to identify and resolve the communication issue associated with the U1870 code.