U01D387 - U01D387 Lost Communication with Rear Right Millimeter Wave Radar

Deep Definition of U01D387 Fault

U01D387 (Loss of Communication with Rear Right Millimeter Wave Radar) is a Vehicle Network Communication Diagnostic Trouble Code (Diagnostic Trouble Code, DTC). Its international classification standard identifier is U class, specifically referring to communication connection anomalies between control units. In the complex vehicle domain controller architecture, this fault clearly points to data link interruption between the Multi-function Video Controller and the Rear Right Millimeter Wave Radar. This communication link is typically built on the Controller Area Network (CAN) protocol, with its core function ensuring visual perception systems and close-range radar sensors can share physical location, relative speed, and obstacle detection data in real time. When the system detects signal integrity loss or timeout response, it will record this fault code to maintain the integrity of the vehicle safety system.

Common Fault Symptoms

After the system identifies failure of the aforementioned communication link, Multi-function Video Controller functionality loss will trigger a series of driving feedback directly perceivable by users, specific manifestations including but not limited to the following situations:

• System Function Degradation: Automatic parking or rear-end collision warning functions relying on Rear Right Millimeter Wave Radar data will be temporarily disabled or unavailable.
• Instrument Panel Status Indication: The dashboard may show a fault indicator light related to the Multi-function Video Controller, prompting the driver to conduct further checks.
• Network Data Stream Anomalies: On the Vehicle Information Infotainment System (IVI), information involving blind-spot monitoring or radar-assisted display may fail to load or show as default status.
• System Self-Test Error Report: When the vehicle enters specific operating conditions, the system startup self-check procedure will read and store this communication loss fault record.

Core Fault Cause Analysis

Regarding the generation mechanism of the U01D387 fault code, based on existing diagnostic data, its root causes can be summarized as anomalies in three dimensions: hardware components, physical connections, and controller logic:

• Hardware Component Failure: Rear Right Millimeter Wave Radar Failure. This refers to substantive damage to the radar's internal transmission/reception units, processing chips or power management modules, resulting in inability to generate effective communication messages.
• Wiring/Connector Failure: Harness or Connector Failure. Due to physical wear, corrosion, loosening or external damage, causing the CAN bus cable connecting the Multi-function Video Controller and Rear Right Millimeter Wave Radar to appear open circuit, short circuit or abnormal ground voltage.
• Controller Logic Operation: CAN Network Failure and Multi-function Video Controller Failure. This may be due to arbitration failure in vehicle network nodes, signal interference or controller internal software logic locking up, resulting in inability to correctly parse or respond to request signals from the Rear Right Millimeter Wave Radar.

Technical Monitoring and Triggering Logic

Control units' determination of U01D387 follows a strict time sequence and status monitoring process, with its triggering mechanism based on the following technical logic:

• Monitoring Target: System continuously monitors communication request signals (Request Signal) and expected response signals (Response Signal) sent by the Multi-function Video Controller to the Rear Right Millimeter Wave Radar. Monitoring focus includes signal voltage duty cycle, message ID consistency, and communication latency time.
• Trigger Conditions: Fault determination strictly depends on vehicle power status, only performing effective network initialization and real-time communication listening when the Start Switch is in ON Position.
• Determination Logic: After the Start Switch is in ON position and the system completes initialization, if the control unit does not receive an effective handshake signal (Valid Handshake Signal) from the Rear Right Millimeter Wave Radar within the prescribed monitoring time window, the system will determine loss of communication, light relevant fault indicator lamp to warn the driver.