Fault code U1001 – a step-by-step guide to diagnosing and fixing it

Error code U1001 is displayed and the check engine light is on - what does this mean?

The DTC U1001 is recognized by the OBD system when there is a communication error in the vehicle's CAN bus network. This error code indicates an interruption or fault in the data transmission between different control units. For various manufacturers, this code may be referred to as "CAN Communication Bus Off" or "Network Communication Malfunction".

What can cause this error code?

• Defective CAN bus wiring
• Damaged plug connections on control units
• Corrosion in the bus lines
• Faulty CAN bus terminating resistor
• Defective control unit in the network
• Short circuit in the CAN high or CAN low cable
• Interruption in the ground line
• Electromagnetic interference due to defective components

What symptoms occur in parallel with error code U1001?

• Communication problems: Various vehicle systems are not working properly
• Warning lights: Multiple indicator lights illuminate simultaneously
• Functional failures: ABS, ESP or other electronic systems are malfunctioning
• Starting problems: Engine does not start or runs irregularly
• Display errors: Instruments show incorrect or no values
• Loss of communication: diagnostic device cannot communicate with all control units

How can the problem with fault code U1001 be resolved?

• Repairing fault code U1001 requires a systematic approach to identifying the communication fault.
• Check and repair the CAN bus wiring: Check all CAN bus cables for damage, breaks or short circuits and replace defective cables
• Clean and secure plug connections: Check all control unit plugs for corrosion, clean and connect securely
• Measure termination resistors: Check CAN bus termination resistors with a multimeter and replace if there is a deviation of 120 ohms
• Test control units individually: Check each connected control unit in isolation and replace defective modules
• Check ground connections: Check all ground cables of the CAN bus system for continuity and tight fit
• Eliminate sources of electromagnetic interference: Identify and replace defective ignition coils, generators or other interfering components