U10B818 - U10B818 MRR Counter Error

Fault Depth Definition

DTC U10B818 indicates a failure in data counter validation between the Front Millimeter Wave Radar (MRR) and the Control Unit within the vehicle's communication network architecture. In the in-vehicle network communication protocol, counters are used to ensure message continuity and synchronization. This fault means that the control unit has not received correctly incremented message count values within the expected communication cycle, or detects an anomaly in the data packet sequence. This usually indicates signal loss, timing desynchronization, or data integrity damage on the communication link, directly affecting the data interaction reliability and functional status of Advanced Driver Assistance Systems (ADAS).

Common Fault Symptoms

When the MRR counter error is recorded, the vehicle system may exhibit the following symptoms related to driving experience or instrument feedback:

• Advanced Driver Assistance Systems (such as Adaptive Cruise Control, Automatic Emergency Braking, etc.) are unavailable or temporarily disabled by the system.
• Warning indicators related to radar sensors or restricted driver assistance systems may illuminate on the dashboard.
• Driver assistance functions relying on front millimeter-wave radar data fail to activate or exit unexpectedly under specific driving conditions.
• The vehicle diagnostic system stores this communication-related fault code, which may be accompanied by abnormal network communication status.

Core Fault Cause Analysis

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

• Hardware Component: The front millimeter-wave radar unit itself has an internal logic fault, causing it to be unable to generate or send the correct counter signal.
• Line/Connector: Fuse failure in the power circuit leads to interruption of radar power supply, or physical connection instability and excessive contact resistance exist in signal transmission wiring and connectors, leading to message transmission loss.
• Controller: Data synchronization failure at the communication protocol parsing level; when consecutive message loss is caused by network load or signal interference, the controller determines that counter validation fails.

Technical Monitoring and Trigger Logic

The system determines this fault through specific electrical conditions and communication status monitoring. The specific logic thresholds and operating conditions are as follows:

• Monitoring Target: Continuity and integrity of communication message counters, focusing on monitoring the loss of any monitored message.
• Value Range: Controller operating voltage must be maintained between $9V$~$16V$, ensuring fault determination under normal electrical conditions.
• Trigger Conditions:
  • System enters monitoring state after completing power-up initialization for $3s$.
  • Loss of any monitored message $10$ consecutive times satisfies the fault setting condition.
  • Private CAN network communication status is normal, and has not entered busoff state.
  • Vehicle factory mode is off, ensuring trigger occurs in non-diagnostic mode.