C1B9500 - C1B9500 LKA Request Value and Slope Exceed Defined Threshold

Fault Severity Definition

DTC ID: C1B9500

This DTC belongs to the key diagnostic information in the Chassis Domain Control Network, primarily targeting the Lane Keeping Assist (LKA) function in the vehicle's active safety system. Its core monitoring object is the LKA intervention command signal received by the Electric Power Steering System (EPS). Specifically, the system continuously monitors the "Request Torque Value" and its rate of change calculated by the ADAS (Advanced Driver Assistance System). When the control unit determines the signal logic is abnormal, this DTC is recorded.

In vehicle control architecture, this DTC defines two key performance indicators: Torque Value Threshold and Torque Slope Threshold. The system aims to ensure smoothness and safety during LKA steering intervention. If command torque exceeds preset physical limits or changes too rapidly, it indicates potential conflicts in the EPS controller or upstream signal source, requiring entry into fault protection mode to prevent unexpected vehicle steering actions.

Common Fault Symptoms

When DTC C1B9500 is illuminated and settings conditions are met, owners and drivers typically perceive the following driving experience changes:

• Steering Function Limited: Steering system control logic enters a degraded mode; LKA active intervention functionality is partially or completely lost, and the vehicle cannot follow navigation-assisted systems for automatic correction.
• Instrument Warning Feedback: The instrument cluster may illuminate the Lane Keep Assist OFF indicator light, or display corresponding ADAS function limitation prompts in the infotainment system.
• Abnormal Steering Feel: Under specific conditions, drivers may feel an abrupt change in assistive torque or a delayed response phenomenon when re-engaging after the system exits.
• Dynamic Stability Warning: Due to partial function loss, vehicle assistance retention ability decreases during cornering, requiring higher intensity manual intervention by the driver to maintain lane center.

Core Fault Cause Analysis

Based on fault data sources and system architecture characteristics, the root causes of this fault can be analyzed from the following three technical dimensions:

1. Wiring and Connector Faults

   • The communication bus or power line between the Electric Power Steering Controller (EPS Controller) and the Multi-Function Video Controller experiences intermittent open circuits, short circuits, or excessive contact resistance.
   • Harness is squeezed or worn causing unstable signal transmission, resulting in distorted torque values during transmission.

2. Hardware Component Failure

   • Electric Power Steering Controller Failure: The EPS control module's internal calculation unit incorrectly processes the request torque signal, or the power actuator on the motor side shows nonlinear deviation in instruction response.
   • Multi-Function Video Controller Failure: This controller is responsible for collecting vehicle image information and calculating LKA intervention strategies; if its logic operation is abnormal, the output initial torque value will directly exceed limits.

3. Controller and Logic Operation Abnormalities

   • The threshold mapping data stored internally in the Control Unit becomes abnormal, causing mis-triggers on normal torque signals.
   • ADAS algorithm output strategies (such as when surfaces are slippery or curves are incorrectly identified) do not conform to the physical execution capability of the steering system.

Technical Monitoring and Trigger Logic

This DTC's triggering follows strict timing threshold determination logic to ensure it is only recorded when a real anomaly occurs, avoiding false alarms on normal vehicle fluctuations. Specific monitoring mechanisms are as follows:

• Pre-conditions (Trigger Condition)

  • Ignition Switch Status: The vehicle ignition switch must be in the ON position.
  • System State Requirement: LKA function must be in an Active Status, meaning the system is activated and monitoring lane lines.

• Monitoring Targets and Parameter Thresholds Subject to pre-conditions, the Electronic Control Unit (ECU) continuously samples and calculates the LKA request signal; once any of the following situations are detected to persist:

  $$ \text{Duration} \ge 80,\text{ms} $$

  And simultaneously satisfies the following numerical criteria:

  • Torque Value Threshold Determination: LKA Request Torque Value exceeds defined threshold: $$ \text{Threshold}_{\text{Torque}} = 3,\text{N}\cdot\text{m} $$
  • Slope Value Threshold Determination: LKA Request Torque Slope exceeds defined threshold: $$ \text{Threshold}_{\text{Slope}} = 10,\text{N}\cdot\text{m}/\text{s} $$

• Logic Conclusion When the above values exceed the specified range and persist within the time window (80ms), the control unit determines the fault is active, records DTC C1B9500, and may illuminate steering system warning lights or disable related driver assistance functions to ensure driving safety.