U102E87 - U102E87 MRR Timeout Communication Lost

Fault Detail Definition

Fault code U102E87 indicates a severe communication integrity interruption in the vehicle's Advanced Driver Assistance Systems (ADAS) network architecture. Specifically, this code is defined as MRR Timeout Lost Communication, meaning the main control unit cannot receive valid data messages from the Front Millimeter Wave Radar (MRR) within the expected time window.

In the vehicle electronic electrical architecture, MRR serves as a key environmental perception sensor, responsible for sending target distance, relative speed, and azimuth information to the domain controller via CAN bus. The triggering of this fault code marks a failure in the heartbeat mechanism or periodic message transmission within the network communication protocol. The control unit detects that the signal feedback loop is open, leading to an inability for the system to confirm the online status of the radar node. This belongs to a network communication class fault (U code), directly affecting functional logic operations dependent on radar data.

Common Fault Symptoms

When the control unit records U102E87 fault code, it indicates that the data link of the front millimeter wave radar has been interrupted. Although specific instrument cluster displays vary by vehicle model strategy, based on the technical logic of communication loss, the system typically exhibits the following functional status feedback:

• Driving Assistance Function Unavailable: Functions dependent on radar data (such as Adaptive Cruise Control ACC, Autonomous Emergency Braking AEB, Forward Collision Warning FCW) will be temporarily disabled or exited due to lack of perception data.
• Abnormal System Status Indication: The dashboard or HUD may display text prompts such as radar sensor restricted, sensor occlusion, or assistance system temporarily unavailable.
• Fault Indicator Light On: Relevant safety system warning lights may illuminate on the dashboard to prompt the driver that there is an abnormality at the communication level of the perception system.

Core Fault Cause Analysis

Based on the physical path and logical levels where the fault occurs, causes leading to U102E87 communication timeout can be classified into the following three core dimensions:

• Hardware Component Dimension Front Millimeter Wave Radar Failure: Hardware failure of internal microprocessors, transceiver modules, or power management units in the radar sensor, causing it to be unable to generate or send communication messages conforming to protocol standards, thereby resulting in signal source loss.

• Wiring/Connector Dimension Harness or Connector Failure: Physical transmission medium between controller and radar is damaged. Includes CAN bus wire open circuit, short circuit, or connector pin oxidation, loosening, causing signal integrity destruction and messages unable to physically transmit. Fuse Failure: Power protection circuit powering the radar sensor blows. This will directly cut off working voltage of radar, leading to node power loss, thus triggering communication timeout.

• Controller Dimension Communication Logic Monitoring Abnormality: Although primarily pointing to radar end, the receiving controller if in specific logical states (such as factory mode, bus error state) may also affect fault determination and recording. This dimension mainly involves configuration of communication protocol stack and state machine management.

Technical Monitoring and Trigger Logic

Control unit monitors communication link through built-in diagnostic monitor for real-time sampling and logical judgment. Fault code U102E87 setting and triggering strictly follow the following technical parameters and operating conditions:

• Monitoring Target and Counting Logic Diagnostic program continuously monitors specific message IDs from front millimeter wave radar. Core logic for fault determination is any monitored message lost consecutively $10$ times. This means within continuous communication cycles, controller did not detect valid signal frames, counter reaches threshold to trigger fault.

• Voltage Working Window Fault determination is only conducted within effective range where controller power supply is stable, to exclude system reset interference caused by low voltage. Effective monitoring voltage range is $9V$~$16V$. Outside this interval, diagnostic logic may be inhibited.

• Time and Status Constraints To ensure system stability, fault monitoring must meet the following specific operating conditions:

  1. Time Delay: Must start monitoring after Power-on Initialization $3s$, to avoid transient fluctuations at system startup moment.
  2. Bus State: Private CAN network must be in normal communication state, i.e., Private CAN not entering bus-off state. If bus is already in offline error state, this node timeout will no longer be determined separately.
  3. Mode Restriction: Diagnostic function is only effective when Factory Mode is Off, ensuring vehicle is in normal user operation mode rather than production debugging mode.