Fault code U1208 – a step-by-step guide to diagnosing and fixing it

Error code U1208 is displayed and the check engine light is on - what does this mean?

The DTC U1208 is a manufacturer-specific fault code that is recognized by the OBD and EOBD systems and indicates a problem in the communication between various control units. This trouble code mainly occurs in General Motors vehicles and indicates a fault in the data transmission between the engine control unit and other vehicle modules.

What can cause this error code?

• Defective CAN bus connection between control units
• Damaged or corroded cable connections in the communication network
• Loose or oxidized plug connections on the control units
• Faulty earth connections in the electrical system
• Defective engine control unit (ECM) or other control units
• Software error in one of the communicating modules
• Voltage drops or unstable vehicle electrical system voltage
• Electromagnetic interference in the vehicle

What symptoms occur in parallel with fault code U1208?

• Starting problems: The vehicle is difficult or impossible to start
• Jerky engine running: Irregular idling and poor engine performance
• Failure of comfort functions: Air conditioning, radio or other electrical systems do not work properly
• Shifting problems: Shifting irregularities may occur with automatic transmissions
• Instrument failure: Displays on the dashboard may flicker or fail
• Increased fuel consumption: Due to faulty communication between the control units

How to fix the problem of fault code U1208?

• Repairing fault code U1208 requires a systematic diagnosis of the communication systems in the vehicle.
• Checking and cleaning all plug connections between the control units, including securing correct plug contacts
• Measuring the vehicle electrical system voltage and checking the battery and charging system for proper function
• Checking the CAN bus lines with a multimeter for continuity, short circuits and correct resistance values
• Checking and repairing the earth connections of all control units involved in the vehicle
• Software update or reprogramming of the affected control units with the latest manufacturer software
• Replacement of defective control units after clear identification of the faulty module through diagnostic tests