U01D108 Invalid Data Received From EPS: Fault Analysis and Technical Description

Deep Fault Definition

U01D108 is a universal automotive diagnostic trouble code (DTC), belonging to the network communication category of faults. The full definition of this DTC is "Invalid Data Received From EPS". In automotive electronic architecture, EPS (Electronic Power Steering) Electric Power Steering System serves as a key power control unit, interacting with other controllers via in-vehicle network bus (e.g., CAN Bus).

When the Multi-function Video Controller attempts to parse messages from the EPS module, if it detects that the information fields in the data frame do not comply with preset protocol specifications, checksum error (Checksum Error) or data format does not match expectations, the system will determine the received data as "Invalid Data". At this time, the communication monitor inside the control unit will record this DTC, marking failure in data integrity verification on the network communication link. This usually means that the EPS controller failed to send effective payload correctly according to the protocol, or there is a deviation in the decoding logic for EPS data at the receiving end.

Common Fault Symptoms

Based on system interaction anomalies and functional dependencies, this DTC may lead to the following phenomena observable by vehicle owners or maintenance technicians:

• Multi-function Video Controller Function Limited: Affected by communication data, some display or control functions integrated in the instrument cluster or multimedia system may fail, for example, electronic mirror adjustment, inside car camera linked display modules may appear intermittent black screen or unable to respond.
• Steering System Related Interaction Anomalies: Since information sent by EPS as a data source is marked as illegal, auxiliary functions relying on steering angle velocity or torque data (such as lane keeping assistance video feedback) may be interrupted.
• Malfunction Indicator Light On: In the dashboard, warning lights related to powertrain control module or network communication fault indicator light may light up, prompting the driver that there is an electronic control system anomaly.
• System Enters Fault Protection Mode: To prevent vehicle misoperation due to unreliable data, relevant subsystems may temporarily lock part of non-essential functions.

Core Cause Analysis

According to the definition of the fault code and system architecture logic, fault causes can be categorized into three dimensions for troubleshooting and understanding:

• Hardware Component Anomalies (EPS System & Multi-function Video Controller)
  • EPS Module Hardware Failure: Communication chip or memory inside the electric power steering control unit may suffer physical damage, causing it to be unable to generate data frames compliant with protocol standards.
  • Internal Circuit Problems of Video Controller: Processor or receiving interface hardware anomaly in the multi-function video controller itself, causing parsing errors for normal data from EPS and false reporting as illegal data.
• Line and Connector Connection Status
  • Physical Connection Interruption: Open circuit, short circuit or ground interference exists in the communication harness between EPS and multi-function video controller.
  • Excessive Contact Resistance: Related connector pin oxidation, loosening or corrosion causes signal transmission quality to drop, leading to receiving end data checksum failure.
• Control Unit Logic Operation (Software & Protocol Matching)
  • Control Strategy Deviation: EPS module calibration data or software version may be incompatible with current video controller, resulting in mismatched data format definitions.
  • Diagnostic Monitor Determination Threshold: Controller internal fault diagnosis logic triggers alarm after startup regarding communication message validity judgment standard.

Technical Monitoring & Trigger Logic

The generation mechanism of this DTC strictly depends on specific electrical states and system activation conditions, its monitoring process is as follows:

• Specific Operating Condition Trigger Conditions

  • Fault judgment is only valid when Start Switch is in ON Position. When ignition switch switches from OFF to ON (or power-on mode), the in-vehicle network communication is activated, at which time the control unit starts polling and receiving EPS node data messages.

• Monitoring Target & Verification Logic

  • Data Validity Check: Multi-function Video Controller immediately performs integrity check on received messages (e.g., ID match, data length checksum) when receiving diagnostic frames or status frames from EPS.
  • Illegal Data Determination Threshold: When received signals do not comply with CAN bus protocol specifications, or data content exceeds the allowed valid range (e.g., value overflow, illegal character encoding), system determines Invalid Data.

• Fault Record & Storage

  • Once continuous or single invalid data responses are detected during power-on cycle, DTC Logic is triggered to generate DTC U01D108, and stored in the control unit's fault memory for subsequent read analysis. This process usually does not accompany maintenance suggestions, aiming to accurately record system communication link status anomaly.