Fault code U1105 – a step-by-step guide to diagnosing and fixing it

Error code U1105 is displayed and the check engine light is on - what does this mean?

The DTC U1105 is a network-related fault code that is recognized by the OBD/EOBD diagnostics when communication problems occur between different control units in the vehicle. This trouble code indicates an interrupted or faulty data transmission in the CAN bus system, which means that important vehicle systems can no longer communicate with each other properly.

What can cause this error code?

• Defective CAN bus cable or interrupted lines
• Corroded or loose plug connections on the CAN bus system
• Faulty control unit (ECU) in the network
• Short circuit in the CAN bus cabling
• Defective terminating resistors in the CAN bus system
• Voltage problems in the vehicle electrics
• Damaged fuses for control unit communication
• Software problems in one of the networked control units

What symptoms occur in parallel with fault code U1105?

• Warning lights: Various indicator lights in the dashboard light up simultaneously
• Functional failures: Individual vehicle systems such as ABS, ESP or air conditioning no longer work
• Starting problems: The vehicle is difficult to start or the engine runs unevenly
• Communication errors: OBD scanner cannot establish a connection to certain control units
• Electrical faults: Irregular behavior of electronic components
• Missing data: Certain vehicle data is no longer displayed in the on-board computer

How to fix the problem of fault code U1105?

• Repairing fault code U1105 requires a systematic diagnosis of the CAN bus system.
• Checking all CAN bus plug connections for tight fit and corrosion, cleaning and retightening the connections
• Measuring the CAN bus voltage with a multimeter and replacing defective cables or repairing interruptions
• Testing the terminating resistors in the CAN bus system and replacing defective resistors with new components
• Diagnosis of all connected control units with a professional diagnostic device and replacement of faulty ECUs
• Checking the power supply to all control units and repairing voltage problems in the vehicle electrics
• Perform software update for all networked control units and delete error code after successful update