C1B9C24 - C1B9C24 Main_Aux_Torque Signal Always High Level

C1B9C24 Main_Auxiliary_Torque Signal Always High Level Fault Description

Detailed Fault Definition

DTC C1B9C24 (C1B9C24 Main/Auxiliary/Torque Signal Always High Level) is a specific diagnostic trouble code in the Electric Power Steering (EPS) system for torque sensor signals. In this control unit's electronic architecture, this code indicates an abnormal constant state has occurred in the feedback loop of the main or auxiliary torque sensors.

In the EPS system's control logic, the torque sensor plays a crucial role, responsible for collecting physical position information regarding the steering wheel's rotation angle and applied torque in real time. Its signal is used to construct a precise pulse signal feedback loop, ensuring the control unit can accurately calculate the required assistance torque. "Always high level" in the fault description means the system has detected that the output signal of the main or auxiliary (or dual-channel) sensor is consistently at the logic power voltage level (i.e., invalid high-impedance state or short to power), completely losing its dynamic characteristics fluctuating with steering action. This continuous fixed high potential state indicates that the feedback loop cannot transmit real physical input information, causing the assistance control system to enter a fault protection mode.

Common Fault Symptoms

After the system determines and stores the C1B9C24 fault code, the vehicle's driving experience and dashboard status usually exhibit the following characteristics:

• Abnormal Steering Feel: Due to the controller being unable to obtain real torque feedback signals, assistance output may be instantly cut off or enter a maximum fixed mode, causing the driver to feel a sharp increase in resistance, heaviness, or abnormal lightness when turning the steering wheel.
• Instrument Fault Indication: The EPS system fault light (yellow warning light) on the vehicle dashboard will illuminate, indicating that the steering system has unreliable data.
• Power Control Logic Failure: Some models may restrict engine output power or activate backup steering mode to ensure driving safety when assistance feedback is lost, but this is usually accompanied by obvious operation lag.

Core Fault Cause Analysis

Based on the raw data for C1B9C24 and combined with automotive electronic architecture analysis, the fault can be attributed to technical logic in the following three dimensions:

• Hardware Component Failure: This dimension involves physical damage to the sensor body or signal processing circuit. In the description of "Torque Sensor Circuit Fault", if internal components of the sensor age or magnetic resistance characteristics change locking the signal source at a high potential, it falls within this category. Such faults usually stem from mechanical stress impact or component life ending.
• Line/Connector Physical Connection Anomaly: This dimension focuses on the quality of signal transmission media and electrical connections. "Torque Sensor Circuit Fault" in the raw data clearly points to problems with the line itself. This may be due to wiring aging leading to a short circuit to the power positive terminal (VCC), or insulation layer damage between signal ground and power pole, causing the control unit to always receive a high voltage signal and unable to distinguish effective logic levels.
• Controller Logic Calculation and Internal Circuit: This dimension involves failures in the EPS controller's internal ADC sampling module or input filtering circuit. In the entry "EPS Controller Internal Fault", if the A/D converter inside the controller responsible for reading external signals is damaged or its processing card appears abnormal discharging, it may misjudge the input status, incorrectly identifying normally varying signals as a continuous high-level state.

Technical Monitoring and Trigger Logic

The determination of this fault code depends on dynamic data stream comparison and voltage threshold logic judgment within the EPS control unit, with specific technical monitoring mechanisms as follows:

• Monitoring Target: The system monitors analog signal voltage values and digital logic levels from the output of the main (Main) and auxiliary (Auxiliary) torque sensors in real time. Under normal conditions, this signal should fluctuate smoothly within a certain range as the steering wheel angle changes; the core goal of fault monitoring is to identify whether the signal deviates from the preset dynamic response interval.
• Trigger Condition Logic: The core of fault determination lies in the "silence" state and "abnormal locking" of the signal. When the system enters driving mode, if the sensor output signal voltage value continues to maintain at the power reference level (i.e., logic high level), rather than switching to a low level or experiencing voltage drop as expected during steering wheel operation, the control system judges this as C1B9C24.
• Specific Operating Condition Requirements: This monitoring is only valid during the dynamic running process of activating the EPS controller drive motor. The system compares data from continuous multiple sampling cycles; if the main/auxiliary signals are confirmed to have no change and maintain a high level during multiple steering operations, the system will generate a fault code and cut off related assistance functions to prevent uncontrolled steering behavior.