U100304 - U100304 Loss of Communication with EPB

Fault Depth Definition

U100304 (Communication Loss with EPB) is a diagnostic trouble code involving internal network interaction within the vehicle's Advanced Driver Assistance Systems. This code defines the communication link interruption status between the Adaptive Cruise Control System (ACC) Control Unit and the Electronic Parking Brake System (EPB) Controller. In the vehicle's Domain Controller Architecture, this fault indicates that the control unit responsible for managing the vehicle's longitudinal control logic failed to receive expected monitoring messages or acknowledgement signals from the EPB controller. Since this system typically operates on a Private CAN (Controller Area Network), the triggering of this code directly reflects an interruption in information exchange between two independent controllers, potentially affecting the vehicle's real-time perception and processing of parking status and safety redundancy data.

Common Fault Symptoms

After the system determines that the setting conditions for this trouble code are met, the driver and onboard systems will exhibit the following specific functional abnormalities:

• Adaptive Cruise System Partial Function Failure: The ACC system may be unable to fully execute distance keeping or cruise control logic, requiring the driver to manually take over steering wheel and pedal operations.
• Dashboard Warning Messages: Related fault lamps may light up on the instrument panel, or prompt messages informing the driver that the current ACC system is in a limited mode.
• Parking Assistance Function Restricted: Due to lack of EPB status signal feedback, the vehicle may be unable to enable or exit auto-hold related logic in certain scenarios.

Core Fault Cause Analysis

Based on the original DTC data and hardware architecture logic, this communication loss problem can be categorized into fault sources from the following three dimensions:

• Hardware Component Failure: Refers primarily to damage to the internal communication module of the electronic parking controller, abnormal sending unit due to physical damage or aging electronic elements in the front millimeter-wave radar, or blown fuses in the power supply end directly cutting off the normal working power supply for the controller.
• Wiring/Connector Failure: Due to breakage caused by wear, squeezing or corrosion of the harness, and connector pin oxidation or loosening, making electrical signals unable to reach the receiver completely during transmission, causing message data packet loss.
• Controller Logic Operation Abnormality: Refers to logical errors in the network communication management unit responsible for the EPB controller or internal software, resulting in inability to correctly parse information sent by the other party, or temporarily interrupting external communication due to internal watchdog mechanism trigger.

Technical Monitoring & Trigger Logic

The control unit's ECU performs continuous health checks on this communication link through preset monitoring algorithms, only recording and storing this fault code when all specific operating condition parameters are met:

• Continuous Message Loss Threshold: System detects any monitoring message lost count reaching 10 times (i.e., any monitoring message consecutively lost $10$ times) within a continuous time period, confirming substantial communication interruption.
• Power Voltage Environment Constraint: The effective range for fault determination requires the controller working voltage to be between $9V$~$16V$, excluding abnormal communication states caused by voltage too low or high.
• Power-On Initialization Timing: The system only begins effective monitoring and determination after the vehicle ignition switch is powered on initialization completed at $3s$ (i.e., $3s$ later).
• Network Status Constraints: When triggering judgment, the private CAN network must not enter BusOff protection state, and system software version must be in factory mode closed normal working configuration.

If any of the above conditions are not met (e.g., voltage outside $9V$~$16V$ range), ECU will not store a fault code for this communication loss event to ensure diagnostic result accuracy.