U01D387 - U01D387 Lost Communication With Rear Right Millimeter Wave Radar

Fault Depth Definition

Fault code U01D387 indicates a specific node communication interruption in the vehicle's internal network architecture. In modern intelligent driving assistance system architectures, the Multi-Function Video Controller serves as the central processing unit and requires continuous data exchange with peripheral sensors. The specific meaning of this fault code is loss of communication with the Right Rear Millimeter-Wave Radar, meaning the control unit cannot receive valid data frames from the Right Rear Millimeter-Wave Radar within a preset time window. This communication loss typically involves missing heartbeat signals or status frames in the Controller Area Network (CAN) protocol, causing the system to determine that the sensor node is unavailable and thereby affecting logic operations and feedback loops dependent on that data stream.

Common Fault Symptoms

When the system detects an abnormality in the communication link and stores this fault code, drivers may perceive the following changes in driving experience or instrument panel feedback:

• Multi-Function Video Controller Function Failure: Core functions relying on video processing and radar fusion cease to function.
• Blind Spot Monitoring System (BSD) or Lane Change Assist System (LCA) becomes unavailable; the dashboard may display warnings related to restricted functionality.
• Rear collision warning feature is missing; the vehicle cannot monitor obstacle distance and relative velocity in the right rear area.
• Automatic parking or panoramic image assist functions may exhibit abnormalities due to lack of data on the right rear space.

Core Fault Cause Analysis

Based on system architecture and signal flow, the causes of this fault can be categorized into the following three technical dimensions:

• Hardware Component Dimension: Right Rear Millimeter-Wave Radar Failure. Damage to internal components within the sensor, abnormalities in the power supply module, or physical damage to the radar antenna prevents it from generating or transmitting valid microwave reflection signals and digital data.
• Wiring/Connector Dimension: Harness or Connector Failure. The physical link between the controller and the radar has open circuits, short circuits, excessive contact resistance, or corrosion of connector pins, resulting in compromised signal transmission integrity.
• Controller & Network Dimension: CAN Network Failure or Multi-Function Video Controller Failure. Excessive load on the network bus causing signal reflection due to abnormal terminal resistance, or the receiving end controller's internal logic unit unable to correctly parse incoming data frames.

Technical Monitoring and Trigger Logic

The system's monitoring of communication status is based on specific conditions and logical judgments to ensure the accuracy of fault records:

• Monitoring Target: The control unit continuously monitors the communication frame frequency and signal validity sent by the Right Rear Millimeter-Wave Radar. The system validates the cyclic redundancy check (CRC) checksum of data packets as well as the continuity of signal timestamps.
• Trigger Condition: The prerequisite for fault judgment is that the Ignition Switch is in the ON Position. In this power mode, the vehicle network wakes up, and the control unit begins executing the node handshake procedure.
• Judgment Logic: If the Multi-Function Video Controller does not receive expected communication signals from the radar node within a specific monitoring period after the Ignition Switch is in the ON Position, or if received signals exceed the valid time threshold, the system will immediately record fault code U01D387 and illuminate the related warning indicator lamp.