U01D387 Communication Loss with RCR Technical Analysis

Fault Depth Definition

U01D387 is a generic code appearing in the vehicle network communication system, specifically indicating an internal communication link abnormality between the Powertrain Control Module (PCM) and other control units. In this case, the fault code explicitly points to a communication interruption between the RCR (Right Rear Camera/Radar System) module and the main controller system.

In the vehicle electronic architecture, the Multimedia Video Controller system acts as a hub for visual data, responsible for real-time acquisition and display of key image data from the rearview camera and millimeter-wave radar. The triggering of U01D387 means that the control unit cannot receive an effective response message from the RCR module within the expected network time window. This communication loss leads to a break in information exchange loops in the onboard network, affecting the normal operating state of driver assistance systems. The system will judge this as a failure at the physical or data link layer between the control unit (ECU) and the remote controller, representing a typical manifestation of network communication faults.

Common Fault Symptoms

When the U01D387 fault code is activated and confirmed as a current fault, owners and drivers may observe the following dashboard feedback or functional anomalies during vehicle operation:

• Video Image Black Screen or No Signal: The full-view image, rearview image, or rear monitoring image on the central control screen disappears completely, displaying a static image or error message.
• Assistance System Function Disabled: Visual feedback modules for blind spot monitoring, automatic emergency braking, or automated parking functions that rely on radar data fail.
• Multimedia Video Controller System Error: The instrument cluster or center screen pops up with system warning information about "Multimedia Video Controller System Function Failure", and the malfunction indicator lamp stays lit.
• Communication Status Indicator Abnormal: Vehicle diagnostic interface reads network communication logs showing interruption of relevant message streams, unable to synchronously update RCR module position and speed data in real-time.

Core Fault Cause Analysis

For troubleshooting the root cause of this fault code, potential problem points need to be broken down into hardware components, line physical connections, and controller logic operations for deep consideration:

• Hardware Component Failure: Mainly involves internal electronic component damage within the right-side millimeter-wave radar system itself, leading to an inability to generate effective network messages; or a communication chip failure inside the Multimedia Video Controller (MVCC) main controller unit.
• Line and Connector Physical Connection: Includes fuses melting for related module power supply, causing circuit open; pin corrosion, open circuit, or short circuit within wiring harnesses; and poor contact at various terminal connectors, leading to unstable signal transmission.
• Controller Logic Operation Anomaly: Refers to erroneous diagnosis logic misjudgment within the control unit, or failure to correctly respond to network reset requests, resulting in continuous recording of communication loss status without returning to normal bus communication mode.

Technical Monitoring and Trigger Logic

The control unit's fault judgment system follows a strict timing monitoring strategy, only outputting a fault code after satisfying specific operating conditions and numerical ranges. The specific trigger logic is as follows:

• Power Voltage Environmental Constraints: The system only performs diagnostic monitoring when the controller voltage is within the normal operating range; the specific voltage threshold is $9V$~$16V$. If the voltage exceeds this range, the system will ignore communication abnormal signals to prevent false alarms due to power fluctuations.

• Initialization and Timing Logic: Fault monitoring must start after vehicle ignition initialization of $3s$; the startup switch must be in the ON position; and it takes effect only after controller voltage stabilizes. Additionally, if the Public CAN bus has not entered the Busoff state (i.e., physical connection layer is normal), and the ECU has not entered the 3s after requesting re-enable DTC detection, the system allows recording this fault.

• Message Loss Judgment Criteria: The core monitoring target is the network message stream. When the system detects that any monitored message is lost continuously for $10$ times, it satisfies the fault confirmation condition. This counting process must continue while the Public CAN bus has not entered the Busoff state to ensure communication interruption is not caused by a physical layer crash. Once the above conditions are judged as complete, the fault code is generated and stored in non-volatile memory.