U111387 - U111387 Message Lost

U111387 Message Lost (U111387 0x27E)

Fault Definition

In automotive electronic network architecture, DTC U111387 indicates integrity verification failure of specific data frame transmission on the vehicle control area network (CAN Bus). Specifically, this code is associated with messages having an identifier of 0x27E (typically involving communication nodes for the Electronic Power Steering System). The appearance of this fault code means that the diagnostic system detected that key periodic signals from the "Electronic Power Steering Controller" failed to pass checksum verification, or expected data frames were not correctly received within the specified window period.

This fault code falls under the diagnosis scope of the Network Communication Layer (Network Communication Layer), and its core function is to monitor the validity of data links in the vehicle network. When the checksum of 0x27E messages appears erroneous, the control unit cannot confirm the authenticity of the data, which will directly lead to partial failure of the Electronic Power Steering Controller functions. The system continuously tracks the duration of checksum errors via a rolling counter mechanism to distinguish from instantaneous interference and persistent faults, thereby avoiding false positives and improving diagnostic accuracy.

Common Fault Symptoms

Based on the technical definition of U111387 fault code and communication logic interruption characteristics, vehicle owners or technicians may observe the following phenomena during driving:

• Electronic Power Steering System Function Degradation: The driver may feel abnormal increase in steering wheel resistance, or partial loss of electric power assist function.
• Instrument Panel Warning Lights On: A steering system failure light (such as a yellow exclamation mark or red ABS light) may appear on the vehicle instrument cluster, indicating the system has entered protection mode.
• Communication Diagnostic Tool Error Reports: When connecting professional OBD scan equipment, communication error codes targeting the Electronic Power Steering Controller are read.
• Network Node Disconnection: The controller may temporarily exit interaction with other control units (such as Gateway or Powertrain Controllers).

Core Fault Cause Analysis

According to the definition of fault code U111387, the root cause is mainly attributed to physical or logical anomalies in three dimensions:

• Hardware Component Anomalies: Internal communication processor of the Electronic Power Steering Controller (EPS Controller) suffers hardware damage, leading to inability to normally generate or process 0x27E messages; or the receiving control unit has a receive circuit fault.
• Wiring and Connector Faults: CAN bus harness connecting the Electronic Power Steering System to the network bus is damaged, such as short-circuit/open-circuit caused by wire sheath damage, or connector pin loose contact/corrosion, leading to signal transmission interruption.
• Controller Logic Operation Anomalies: Internal communication management module of the Electronic Power Steering Controller suffers logic errors, unable to send checksum-correct message data within preset communication cycles, thereby triggering persistent error judgment.

Technical Monitoring and Trigger Logic

The trigger mechanism of this fault code is based on strict time windows and counting logic, specific monitoring parameters as follows:

• Monitoring Target: CAN network message frame data with identifier 0x27E emitted by the Electronic Power Steering Controller.
• Checksum Mechanism: System performs physical layer checksum error detection for every received 0x27E message.
• Counting Logic: System maintains a rolling counter, continuously accumulating time only when checksum errors occur. When the counter indicates the duration of the checksum error state reaches a set threshold and the state persists, the fault code will be marked as "Set".
• Trigger Condition Value: Checksum error rolling counter error persists for $120\text{ms}$.

This logic design aims to filter momentary signal jitter caused by electromagnetic interference (EMI). Only when the error state is continuously maintained above $120\text{ms}$ during drive motor operation or normal communication windows, will the system judge it as a definite fault and trigger DTC U111387 to ensure diagnostic accuracy and driving safety.