U111386 - U111386 Message Invalid

Deep Definition of Fault

DTC U111386 is defined as "Invalid Message", categorized as a Class U network communication fault within the Electric Power Steering (EPS) control architecture. This code precisely localizes to the specific data stream with Frame ID 0x27E, indicating that integrity check validation failed on the signals received by the system. From a technical principle perspective, this fault involves verification mechanisms at the data transmission layer, specifically focusing on the invalid status of DST (Domain Terminal System) messages, manifesting as failing validation for the Rolling Counter (RC) and Check Sum (CS). The control unit continuously monitors network communication health; upon receiving messages from specific nodes, it ensures sequential logic continuity of sequence numbers and that data bit error detection codes meet preset algorithms. Any deviation may trigger this DTC to alert on network architecture anomalies.

Common Fault Symptoms

• The Electronic Power Steering Controller enters a partial function-limited mode, causing drivers to perceive significant reduction in assist torque or intermittent failure when operating the steering wheel.
• Fault indicator lights on the instrument cluster (e.g., EPS warning light, Vehicle Stability System light) may illuminate or flash, indicating vehicle network communication warnings.
• Vehicle steering response characteristics change, possibly experiencing heavy steering feel, uneven assist, or steering lag and other dynamic performance degradation phenomena.
• OBD-II diagnostic tools can read U111386 communication class fault codes, indicating that the controller has recorded checksum error events internally.

Core Fault Cause Analysis

Based on raw data and system architecture logic, fault roots can be summarized into the following three technical dimensions:

• Hardware Component Anomalies: Communication modules or processing chips inside the Electronic Power Steering Control Unit (ECU) suffer functional damage, resulting in inability to correctly generate, validate, or parse Check Sum (CS) and Rolling Counter (RC) data.
• Wiring and Connector Physical Connections: CAN bus harnesses exhibit aging, wear, open circuits, or short circuits; additionally, connectors may have pin oxidation, poor connection, or looseness, leading to degraded signal transmission quality, preventing the receiver from correctly comparing checksums.
• Controller Logic Operation Failures: Network configuration errors or communication protocol stack anomalies within the control unit cause rolling counter synchronization failure or deviation in algorithm determination during dynamic data transmission, resulting in messages being marked as invalid by the system.

Technical Monitoring and Trigger Logic

The system judges specific fault occurrence conditions through real-time monitoring strategies to ensure accuracy and safety of fault determination:

• Monitoring Targets: Control units focus on monitoring message data integrity for Frame ID 0x27E in the CAN network, with core indicators being Check Sum (CS) values and Rolling Counter (RC) continuity.
• Value Range Judgment: The system maintains an error rolling counter error timer; accumulation begins when checksum errors or rolling counter status jumps are detected. If such error duration reaches $120ms$, the fault trigger threshold is satisfied.
• Specific Conditions: This monitoring logic is effective during vehicle power operation and steering execution, aiming to ensure real-time reliability of the steering system in network communication environments. Only when valid signals matching checksum and rolling counter status cannot be received continuously for more than $120ms$, will the system formally record DTC U111386 and enter fault storage mode.