U1935 – CAN Communication Bus Fault.

The ODBII code U1935 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a communication issue between modules in the vehicle’s network.

The severity of ODBII code U1935 CAN Communication Bus Fault is generally considered moderate to severe.

Common Causes For: U1934 U1934: “Module Communication Failure”

• Faulty CAN bus wiring or connectors
• Malfunctioning CAN bus modules
• Short circuits in the CAN bus
• Open circuits in the CAN bus
• Interference from other electrical components
• Faulty or damaged ECU (Electronic Control Unit)
• Poor ground connections
• Corroded or damaged terminals
• Software issues or bugs in the ECU
• Incompatible or faulty aftermarket accessories

Common misdiagnosis for U1935 CAN Communication Bus Fault.

• Faulty Engine Control Module (ECM)
• Defective Body Control Module (BCM)
• Bad wiring or connectors
• Malfunctioning CAN bus transceiver
• Incorrectly programmed modules
• Power supply issues
• Faulty sensors or actuators
• Software glitches in the vehicle’s computer systems

Common Troubleshooting Steps

The OBD-II code U1935 indicates a CAN (Controller Area Network) communication bus fault. This code typically suggests that there is a problem with the communication between 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 trouble codes that may be present. Other codes can provide additional context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the CAN bus. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors at the ECM (Engine Control Module), BCM (Body Control Module), and any other modules that communicate over the CAN bus.
• Test the CAN Bus Voltage:
• Use a multimeter to check the voltage levels on the CAN High (CAN H) and CAN Low (CAN L) wires. The typical voltage levels should be around 2.5V when idle and should fluctuate between 2.0V and 3.0V when the bus is active.
• If the voltage levels are outside this range, there may be a fault in the wiring or a module.
• Check for Short Circuits:
• Use a multimeter to check for short circuits between the CAN H and CAN L wires and ground or each other. A short circuit can cause communication failures.
• Inspect Modules:
• Check the modules on the CAN bus for proper operation. If one module is malfunctioning, it can disrupt communication for the entire bus.
• If possible, disconnect modules one at a time to see if the code clears or communication is restored.
• Look for Interference:
• Ensure that there are no aftermarket devices or modifications that could be interfering with the CAN bus communication.
• Check for Ground Issues:
• Ensure that all ground connections related to the CAN bus are secure and free of corrosion. Poor grounding can lead to communication issues.
• Perform a Network Test:
• If you have access to a professional-grade scan tool, perform a network test to check the integrity of the CAN bus and identify any faults.
• Clear Codes and Test Drive:
• After performing the above checks and repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns.
• Consult Service Manual:
• Refer to the vehicle’s service manual for specific diagnostic procedures and wiring diagrams related to the CAN bus system. 1
• Seek Professional Help:
• If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with CAN bus systems. By following these troubleshooting steps, you should be able to identify and resolve the issue causing the U1935 code.