U1709 – CAN Communication Bus Fault.

The ODBII code U1709 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a problem with data transmission between modules in the vehicle’s network.

The severity of ODBII code U1709 CAN Communication Bus Fault is generally considered moderate to severe.

Common Causes For: U1708 U1708: Transmission Control Module Communication Error

• Faulty CAN bus wiring or connectors
• Defective CAN bus module
• Short circuit in the CAN bus
• Open circuit in the CAN bus
• Interference from other electrical components
• Poor ground connections
• Faulty or incompatible aftermarket accessories
• Software issues or bugs in the vehicle’s control modules

Common misdiagnosis for U1709 CAN Communication Bus Fault.

• Faulty Engine Control Module (ECM)
• Faulty Transmission Control Module (TCM)
• Bad wiring or connectors
• Faulty Body Control Module (BCM)
• Defective sensors
• Battery or charging system issues
• Faulty CAN bus transceiver
• Software issues or updates needed
• Grounding issues
• Intermittent electrical connections

Common Troubleshooting Steps

The OBD-II code U1709 indicates a CAN (Controller Area Network) communication bus fault. This code typically suggests that there is a problem with the communication between the various modules in the vehicle. 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 related trouble codes. Sometimes, multiple codes can provide more context about the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the CAN bus. Look for any signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors at the ECM (Engine Control Module) and other modules on the CAN bus.
• Test the CAN Bus Voltage:
• Use a multimeter to check the voltage levels on the CAN High and CAN Low wires. The typical voltage levels should be around 2.5V when the bus is idle.
• If the voltage levels are outside the expected range, there may be a short or open circuit.
• Check for Short Circuits:
• Inspect the CAN bus wiring for any shorts to ground or power. A short can disrupt communication between modules.
• Test Individual Modules:
• If possible, isolate and test individual modules on the CAN bus to determine if one of them is causing the communication fault.
• Disconnect each module one at a time and check if the code persists.
• Check for Interference:
• Look for any aftermarket devices or modifications that may interfere with the CAN bus communication, such as alarms, stereo systems, or other electronic devices.
• Scan for Module Communication:
• Use a scan tool to check if all modules on the CAN bus are communicating properly. Some scan tools can perform a network test to identify communication issues.
• Inspect Ground Connections:
• Ensure that all ground connections for the modules are secure and free of corrosion. Poor ground connections can lead to communication issues.
• Check for Software Updates:
• Sometimes, a software update for the vehicle’s modules can resolve communication issues. Check with the manufacturer for any available updates.
• Replace Faulty Components:
• If a specific module is identified as faulty, it may need to be replaced. Ensure that the replacement module is compatible with your vehicle. 1
• Clear Codes and Test Drive:
• After performing repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns. 1
• Consult a Professional:
• If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who specializes in automotive electronics. By following these troubleshooting steps, you can systematically identify and resolve the underlying issue causing the U1709 code.