U013400 - U013400 Lost Communication with EPS (Electric Power Steering) Module

Fault Definition

DTC U013400 indicates that within the vehicle network architecture, the master control unit cannot receive valid data frames from the Electric Power Steering (EPS) Control Module. In modern vehicle electronic architectures, the EPS module is not only responsible for steering assist but also transmits key status information such as steering angle velocity and torque requests to other domain controllers (e.g., Adaptive Cruise Control Unit) in real time via the CAN bus. When the communication link is interrupted, it means the data feedback loop is broken, causing driver assistance functions dependent on steering data to fail closed-loop operation.

Common Fault Symptoms

• Dashboard displays an unavailable or function-limited warning for the Adaptive Cruise Control (ACC) system.
• The vehicle cannot activate or maintain a preset cruise follow status.
• Related driver assistance system indicators light up abnormally.

Core Fault Cause Analysis

• Hardware Components: A fuse in the power supply circuit blows, causing the EPS module to lose power input; or the power management unit inside the electronic power steering controller is damaged.
• Wiring/Connectors: The CAN bus wiring connecting the EPS module to the gateway or master control unit has open circuit or short circuit issues; physical connectors show pin corrosion, loosening, or poor contact.
• Controller: A fault in the internal logic operation unit of the electronic power steering controller causes an inability to generate or transmit communication messages compliant with protocol standards.

Technical Monitoring and Trigger Logic

• Monitoring Target: The system continuously monitors status message frames from the EPS control module on the CAN bus.
• Judgment Threshold: When any key monitoring message is consecutively lost $10$ times, the communication timeout counter overflows.
• Specific Conditions: The fault determination logic is activated only when the ignition switch is in the ON position power state, at which time the network management system enters wake-up state and begins to verify node alive signals.