U1799 – Control Module Communication Failure

The ODBII code U1799 indicates a “Control Module Communication Failure,” meaning there is a problem with communication between the vehicle’s control modules, which can affect various systems and functions.

The severity of ODBII code U1799 is moderate.

Common Causes For: U1798 U1798: ECM-TCM Communication Failure

• Faulty control module
• Poor electrical connections
• Damaged wiring harness
• Corroded connectors
• Software issues or bugs
• Low battery voltage
• Interference from aftermarket devices
• Faulty CAN bus communication
• Grounding issues
• Malfunctioning sensors or actuators

Common misdiagnosis for U1799 U1799: “Control Module Communication Failure”

• Faulty control module
• Wiring issues
• Poor ground connections
• Corrupted software/firmware
• Faulty sensors
• Communication network issues (CAN bus problems)
• Battery or power supply issues
• Intermittent connection problems

Common Troubleshooting Steps

The OBD-II code U1799 indicates a “Control Module Communication Failure.” This code typically suggests that there is a problem with communication between the vehicle’s control modules. 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, U1799 may be accompanied by other codes that can provide more context about the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the control modules. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the wiring harnesses that connect the affected modules.
• Check Power and Ground:
• Ensure that the control modules have proper power and ground connections. Use a multimeter to check voltage and ground continuity.
• If there are issues with power or ground, repair the wiring or connections as needed.
• Test Control Modules:
• If possible, test the affected control modules to ensure they are functioning correctly. This may involve using specialized diagnostic tools or swapping with known good modules.
• Check for any software updates or reprogramming that may be required for the modules.
• Inspect the CAN Bus:
• The communication between control modules often occurs over a Controller Area Network (CAN) bus. Inspect the CAN bus wiring for damage or shorts.
• Use a scan tool to monitor the CAN bus for any irregularities in communication.
• Check for Interference:
• Look for any aftermarket devices or modifications that may interfere with the communication between control modules. This includes alarm systems, stereo systems, or other electronic devices.
• Clear Codes and Test Drive:
• After performing any 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 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 control module communication.
• Seek Professional Help:
• If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or dealership for further diagnosis. They may have access to advanced diagnostic tools and resources. By following these steps, you can systematically identify and address the underlying cause of the U1799 code.