U1874 – refers to a communication issue between the transmission control module (TCM) and other control modules in the vehicle.

The ODBII code U1874 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 U1874 is generally considered moderate to severe.

Common Causes For: U1873 refers to a communication issue between the Body Control Module (BCM) and the Instrument Panel Cluster (IPC).

• Faulty Transmission Control Module (TCM)
• Damaged wiring or connectors
• Poor ground connections
• Corroded terminals
• Faulty Engine Control Module (ECM)
• Software issues or bugs
• Low battery voltage
• Faulty CAN bus communication
• Intermittent electrical connections
• Malfunctioning sensors related to transmission

Common misdiagnosis for U1874 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)
• Bad ground connections
• Incorrectly diagnosed transmission problems
• Software issues or updates needed
• Faulty sensors (e.g., speed sensors)
• Battery or charging system problems
• Corrupted data or communication protocols
• Other control module failures

Common Troubleshooting Steps

When dealing with OBD-II code U1874, which indicates a communication issue between the Transmission Control Module (TCM) and other control modules in the vehicle, you can follow these common troubleshooting steps:

• Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context and help identify related issues.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the TCM and other control modules. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the wiring harnesses that connect the TCM to the vehicle’s network.
• Check for Short Circuits or Open Circuits:
• Use a multimeter to test for continuity in the wiring. Check for any short circuits or open circuits that could be causing communication issues.
• Inspect the TCM:
• Ensure that the TCM is securely mounted and that there are no signs of physical damage.
• If possible, check the TCM for any software updates or reprogramming needs.
• Test the Communication Network:
• Use a scan tool to monitor the communication between the TCM and other modules. Check for any irregularities in data transmission.
• If you have access to a professional-grade scan tool, you can perform a network test to identify communication failures.
• Check Power and Ground:
• Verify that the TCM is receiving proper power and ground. Use a multimeter to check voltage at the TCM connector.
• Ensure that all ground connections are clean and secure.
• Inspect Other Control Modules:
• If the TCM is communicating with other modules, check those modules for faults or issues that could be affecting communication.
• Look for any signs of water intrusion or damage in other control modules.
• Clear Codes and Test Drive:
• After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner.
• Take the vehicle for a test drive to see if the code reappears.
• Consult Technical Service Bulletins (TSBs):
• Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to U1874.
• Consider Professional Diagnosis:
• If the issue persists after performing these steps, it may be necessary to consult a professional technician or dealership for further diagnosis. They may have access to specialized tools and resources to pinpoint the problem. By following these steps, you can systematically identify and resolve the communication issue indicated by the U1874 code.