Fault code U1200 – a step-by-step guide to diagnosing and fixing it

Error code U1200 is displayed and the check engine light is on - what does this mean?

DTC U1200 is a network communication error that is detected by the OBD system when communication between different control units in the vehicle is interrupted. This fault code mainly affects the CAN bus system (Controller Area Network) and can have different specific meanings for different manufacturers, although it usually indicates communication problems between ECUs.

What causes can this error code have?

• Defective CAN bus cable or damaged wiring
• Corroded or loose plug connections in the communication network
• Failed control unit (ECU/PCM)
• Defective CAN bus termination resistors
• Short circuit or interruption in the data line
• Voltage problems in the vehicle electrical system
• Defective gateway modules
• Electromagnetic interference

What symptoms occur in parallel with fault code U1200?

• Communication faults: Various vehicle systems are not functioning properly
• Warning lights: Multiple indicator lights illuminate simultaneously
• Functional failures: ABS, ESP or other electronic systems do not work
• Starting problems: The vehicle is difficult or impossible to start
• Instrument failure: Speedometer, rev counter or other displays do not work
• Missing diagnostic data: OBD scanner cannot connect to certain modules

How to fix the trouble code U1200 problem?

• Repairing trouble code U1200 requires a systematic diagnosis of the communication network.
• Check and repair the CAN bus cabling: Check all data cables for damage, breaks or short circuits and replace defective cables
• Clean and secure plug connections: Check all relevant connectors on the CAN bus system for corrosion, clean and connect securely
• Carry out ECU diagnostics: Use professional diagnostic equipment to test all ECUs and replace defective modules
• Measure termination resistors: Check CAN bus termination resistors for correct value (120 Ohm) and replace if necessary
• Stabilize vehicle electrical system voltage: Test battery and alternator, charge or replace weak battery
• Replace gateway module: If the communication gateway is defective, replace the module with a new one and program it