U109086 - U109086 ADS Signal Invalid

U109086 ADS Signal Invalid Fault Deep Analysis

### Fault Depth Definition

In vehicle electrical/electronic architecture, DTC U109086 ADS Signal Invalid involves logical verification of key sensing and control signals. This DTC indicates that the relevant Control Unit has determined the received ADS (Automated Driving System or Adaptive Cruise Control Data Stream) signal to be in an untrustworthy state when receiving automated data required by the Adaptive Cruise Control System (ACC) or Advanced Driver Assistance Systems (ADAS). This signal is a core variable in the system's closed-loop feedback loop, used to confirm effective sensor detection of the surrounding environment and status feedback from actuators. When the control unit cannot parse compliant ADS data streams within the specified communication protocol window, the system will flag it as an invalid signal, thereby triggering a protective limitation mode to ensure driving safety.

### Common Fault Symptoms

When DTC U109086 ADS Signal Invalid is activated, the vehicle will exhibit the following perceivable driving experience changes and instrument feedback:

• Adaptive Cruise System Function Failure: ACC function may be forced off or enter a sleep state; the cruise control indicator icon on the dashboard turns off.
• System Warning Information Display: Center console screen or instrument cluster displays relevant alert text such as "Adaptive Cruise Unavailable" or "Radar Signal Lost".
• Dynamic Driver Assistance Limitations: The vehicle may lose the ability to automatically adjust set speed and following distance, requiring driver takeover of vehicle control.

### Core Fault Cause Analysis

According to diagnostic data, the root cause of this fault is primarily attributed to abnormalities in three dimensions: physical components, connection status, and control logic.

1. Hardware Component Failure

   • Right Rear Millimeter Wave Radar System Fault: This is one of the core hardware reasons leading to invalid ADS signals. When sensors or transmit/receive modules integrated within the Right Rear Millimeter Wave Radar (located at the rear of the vehicle) suffer physical damage or performance degradation, their generated echo data cannot be parsed, leading to incomplete ADS message content delivered to the control unit or failed verification.

2. Wiring and Connector Connections

   • Although wiring issues are not explicitly listed, in signal invalid scenarios, communication lines between the millimeter wave radar and the control unit (such as CAN-H/CAN-L) typically exhibit high resistance, short circuits, or open circuits, causing physical interruption of ADS data transmission.

3. Controller and Logic Operation

   • Control Unit Internal Fault: The domain controller responsible for processing radar data may experience internal storage errors or signal processing capacity saturation, resulting in an inability to correctly identify valid ADS input packets.
   • Communication Status Abnormality: Under normal transmission on the Public CAN network, if the control unit internally determines that the received data stream does not conform to preset protocol specifications, it will also be flagged as invalid.

### Technical Monitoring and Trigger Logic

The control system determines the exactness of this DTC through complex real-time monitoring algorithms, and all of the following conditions must be met simultaneously for fault storage and activation:

• Power Voltage Monitoring

  • The power voltage range detected by the controller must be outside or at a critically unstable state of the stable interval $9V$~$16V$. If voltage exceeds this standard range but other logic has not reset, it will trigger an invalid signal determination.
  • Note: The baseline environment for fault determination is within the normal fluctuation range of the power network.

• Timing and Initialization Logic

  • The system must undergo a complete power-on initialization process, waiting $3s$ after startup. This time window ensures hardware self-check is completed and the system enters working state.
  • Service Detection DTC & $3s$ Later: The control unit detects DTC signals in service monitoring mode and locks fault records after maintaining this state for $3s$.

• Communication Network Status

  • Public CAN Not in Bus-Off State: Despite the invalid ADS signal, the Public Controller Area Network (CAN) bus is not in a Bus-Off (disabling error) state, proving that the physical link still has activity, with the issue focusing on data validity or local modules.

• Vehicle Mode and Signal Interlock

  • Factory Mode Disabled: Fault determination occurs only in normal user mode; if the system is in factory debugging mode, this DTC setting condition is ignored.
  • No BCM Power Cut Notification Received: The Body Control Module (BCM) has not sent specific power cut commands, and the controller itself has not received a power-down confirmation signal from the BCM, indicating that the system is still within normal working voltage logic.