U01EA87 - U01EA87 Private CAN Communication TIMEOUT Fault

Fault Depth Definition

U01EA87 represents the "Private CAN Communication TIMEOUT Fault" in the Adaptive Cruise Control (ACC) system. In automotive electronic architecture, the Private CAN network serves as an internal high-speed communication bus, undertaking key subsystems' high-frequency data exchange tasks. This fault code activation means the vehicle control unit did not receive expected acknowledgment signals or valid data packets from the target node within a preset time window. Such communication interruptions directly compromise the data integrity of closed-loop control loops, causing functions relying on real-time message transmission (such as Adaptive Cruise Control) to fail to maintain normal operating conditions, thereby affecting the logical stability of vehicle driving assistance systems.

Common Fault Symptoms

When the system detects this fault code, drivers and instrument panels typically show the following feedback characteristics:

• ACC Function Failure: The active function of the Adaptive Cruise Control system is completely disabled, and the ACC indicator light on the dashboard may light up a fault warning lamp.
• Loss of Vehicle Speed and Following Distance Control: The vehicle cannot automatically maintain preset cruising speed or safe distance with preceding vehicles, requiring manual intervention to take over driving operations.
• System Limit Protection: To prevent further accumulation of data errors, the control unit may enter limp mode or restrict access permissions for some related functions.

Core Fault Cause Analysis

Regarding the phenomenon of Private CAN communication timeout, principle analysis needs to be conducted from the following three technical dimensions:

• Hardware Component Anomaly: Involves internal communication module physical damage of end nodes participating in Private CAN communication (such as gateway, actuator or sensor controller), causing inability to send or receive data frames.
• Line and Connector Connection Status: The physical link of the Private CAN bus exists impedance abnormalities, short circuits, open circuits, or excessive contact resistance, hindering normal transmission of electrical signals, causing signal loss.
• Controller Logic Operation Judgment: Firmware in the control unit experiences deviation in timeout judgment threshold calculation when parsing message streams, or fails to correctly identify valid bus idle states during communication protocol handshaking stages.

Technical Monitoring and Trigger Logic

The system monitors Private CAN communication status in real-time based on strict electrical and time parameters. Fault determination requires meeting the following specific trigger conditions:

• Monitoring Target: Controller power supply voltage stability and CAN message response time (Latency).
• Voltage Range Requirement: System monitoring occurs when controller working voltage is within stable range of $9V$~$16V$.
• Time Delay Judgment: Within $3s$ after system power-on initialization, communication connection must be successfully established and enter normal working state.
• Bus Status Monitoring: System confirms Private CAN network has not entered Busoff state (i.e., node not forced off), but still cannot receive expected communication messages.
• Mode Dependency Conditions: Fault is recorded and stored only under conditions where Factory Mode is Off (Normal User Mode).