Fault code U0001 – a step-by-step guide to diagnosing and fixing it

Error code U0001 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system detects a communication error in the CAN bus network (Controller Area Network), which means that data transmission between different control units is disrupted. This DTC U0001 affects basic vehicle communication and can have slightly different characteristics for different manufacturers, although the core problem of faulty bus communication remains identical.

What causes can this error code have?

• Defective CAN bus lines or cable breakage
• Corroded or loose plug connections in the bus system
• Faulty terminating resistors in the CAN network
• Defective control unit sending incorrect signals
• Short circuit in the CAN bus cabling
• Malfunctions due to electromagnetic interference
• Voltage problems in the vehicle electrics
• Water damage to bus components

Which symptoms occur in parallel with error code U0001?

• Communication faults: Various vehicle systems do not function properly or fail completely
• Instrument panel problems: Irregular displays, flickering warning symbols or complete failure of the displays
• Starting problems: The vehicle is difficult to start or does not start at all
• Electronic system failures: ABS, ESP, air conditioning or other electronic systems operate incorrectly
• Intermittent faults: Problems occur sporadically and disappear again
• Multiple fault codes: Simultaneous occurrence of different trouble codes in different systems

How can the problem with error code U0001 be rectified?

• The repair requires a systematic diagnosis of the CAN bus system in order to identify the exact source of the fault.
• Check and repair CAN bus cables: Complete inspection of all bus cables for damage, breaks or short circuits with subsequent repair or replacement of the defective cable sections
• Clean and secure plug connections: Disassemble all CAN bus connectors, clean thoroughly, check for corrosion and treat with contact spray, then reconnect firmly and correctly
• Measure and replace terminating resistors: Perform resistance measurement at the CAN bus ends (should be 60 ohms between CAN high and CAN low) and replace defective resistors
• ECU diagnostics and replacement: Test individual ECUs with diagnostic device, identify faulty ECUs and replace with new or repaired units
• Eliminate sources of electromagnetic interference: Check retrofitted electronic devices and properly shield or remove, as well as check ignition cables and other potential sources of interference