U102E87 - U102E87 MRR Communication Timeout

DTC Code Definition

DTC code U102E87 is defined as MRR Timeout Loss of Communication, which in vehicle diagnostic protocols represents an interruption in interaction between the Network Communication Control Unit and the Millimeter Wave Radar (Millimeter Wave Radar, MRR) module. In automotive electronic architecture, Blind Spot Monitoring Systems (Blind Spot Monitoring System, BSM) or related active safety functions are highly dependent on frequent data exchange between radar sensors and the master controller. When the master controller does not receive expected monitoring messages within a specific time window, the system determines it to be a communication timeout. This DTC indicates that control logic cannot obtain physical position and rotation speed information used for real-time feedback (for radar monitoring scope), potentially causing reduced perception capability of driver assistance systems, constituting a serious communication class fault diagnosis item in the vehicle network architecture.

Common Fault Symptoms

After triggering this DTC, the vehicle instrument panel and human-machine interaction system provide explicit status information to the driver. Based on the original data description, the specific manifestations during fault occurrence are as follows:

• Blind Spot Monitoring System Partial Function Failure: Related radar sensors (such as front or left rear corner) cannot output effective monitoring signals, resulting in blind spot warning, lane change prompts, etc., being temporarily disabled or unavailable.
• Instrument Panel Warning Light Illuminated: The body domain controller will receive the fault logic determination result and display system communication interruption or no radar signal icons on the instrument screen or warning light area.
• Driver Assistance Limitation Mode: The vehicle may automatically enter a degraded mode, restricting some advanced driver assistance functions (ADAS) that rely on radar perception.

Core Fault Cause Analysis

According to diagnostic definitions, potential sources leading to U102E87 DTC setting can be summarized into the following three dimensions of hardware or circuit anomalies:

• Power Supply Components (Fuse Failure): If the fuse responsible for the radar module or control unit is blown, it will cause a complete interruption in the power supply link, making it impossible to maintain the reference voltage required for communication protocols.
• Wiring and Connector Physical Connections (Harness or Connector Fault): Signal transmission paths experience open circuits, short circuits, or pin withdrawal phenomena, causing data messages to be lost or waveforms distorted during transmission, leading to communication timeout.
• Radar Control Unit Hardware Failure (Controller Fault): Specifically involves internal logic operation errors or chip damage in the controller of the front millimeter-wave radar or left rear corner radar, preventing it from sending monitoring messages according to cycles.

Technical Monitoring and Trigger Logic

The vehicle Electronic Control Unit determines whether fault recording conditions are met through strict software logic, ensuring minimization of false reports. The specific working conditions and technical monitoring parameters for this fault determination are as follows:

• Monitoring Target: Focus on monitoring the existence and integrity of network communication messages, that is, whether valid data frames from MRR are received within a preset window by the receiver end.
• Fault Setting Conditions: Logic determination requires any single monitoring message to be lost 10 times consecutively. The system does not mark fault due to a single packet loss, but instead confirms persistent interruption of the communication link through a counting mechanism.
• Trigger Fault Condition Parameters:
  • Controller Voltage Range: System operation is in a stable power supply state, with an effective detection range of $9V \sim 16V$. If voltage exceeds this range, it may be determined as power abnormality rather than communication fault.
  • Time Window Monitoring: Communication cycle monitoring starts after 3s of power-on initialization, ignoring network oscillation during vehicle startup.
  • CAN Bus State Requirement: Private CAN not entered busoff state. If the bus enters Bus-off state, it is regarded as bus hardware fault rather than MRR specific message loss.
  • Mode Restriction: Valid only in normal user operation mode with factory mode off, excluding interference from engineering debugging modes.