C1B9C23 - C1B9C23 Main_Aux_Torque Signal Always Low Level

Fault Depth Definition

In Electronic Power Steering System (EPS) communication and execution architecture, DTC code C1B9C23 is clearly defined as "Master/Sub Torque Signal Always Low Level". The core role of this fault code lies in reflecting the control unit's monitoring status of input signal integrity. Specifically, this diagnostic logic is used to provide real-time feedback on motor physical position and rotational speed information, serving as the basis for EPS actuator assist calculation.

From a system level perspective analysis, when the EPS controller detects that the sensor signal voltage has remained in a low-level state for a long time, it means the conversion link from physical quantity to electrical signal has been cut off. This system usually employs a redundant design (Master/Sub dual channel); if this double feedback loop remains in an invalid low-voltage logic state continuously, the control unit cannot complete precise identification of driver steering intent, thereby triggering protection mechanisms. The existence of this code marks that severe abnormalities have occurred at the electrical connection level of the system's input signal source or processing module, belonging to a critical system diagnostic fault code.

Common Fault Symptoms

Based on the hardware failure characteristics of C1B9C23 Master/Sub Torque Signal persistent low level, drivers and technicians can observe the following specific manifestations:

• EPS warning light on the dashboard remains illuminated or flashes intermittently, indicating the steering system is in an abnormal monitoring state.
• The steering assist system may suddenly lose regulation capability, resulting in a heavy steering wheel feel or abnormal looseness sensation.
• Under specific torque load conditions, the steering assist motor may enter a safety restriction mode (Limp Mode).
• The vehicle dashboard may simultaneously display communication interruption prompts related to the steering system control unit.
• System logs will continuously record the fault code C1B9C23 Master/Sub/Torque Signal Always Low Level, and it is usually unable to be cleared through conventional hot restart reset.

Core Fault Cause Analysis

According to diagnostic logic and hardware architecture, the reasons leading to the generation of this fault code need to be checked and confirmed from the following three dimensions:

• Hardware Component Failure: Primarily points to Torque Sensor Circuit Failure. The physical sensor component may fail due to aging, moisture or internal circuit open, resulting in an inability to produce the expected high-level signal output.
• Wiring and Connector Anomalies: Includes power ground loop interruption, wiring harness wear causing short circuit to Ground, or connector terminal corrosion poor contact. Such situations will force signal voltage down to low level threshold.
• Controller Internal Failure: Points to EPS Controller Internal Failure. This could be damage to the signal processing module inside the control unit, causing it to mistakenly judge a normal intermediate state as an invalid low-level input, belonging to core failure at the logic operation or hardware level.

Technical Monitoring and Trigger Logic

The generation of this fault code follows strict electrical parameter monitoring standards and control strategies, with specific logic as follows:

• Monitoring Target: System continuously monitors voltage signal and impedance characteristics at the output end of Torque Sensor.
• Value Range Judgment: When signal voltage is detected to be in a low-level state (usually close to $0V$ or ground potential), and this state does not comply with expected excitation voltage range, it is judged as abnormal.
• Trigger Condition: Fault is not detected only at ignition instant, but evaluated in real-time during dynamic monitoring after EPS system power-on and steering motor drive period.
• Judgment Logic: If master signal and auxiliary signal (Master/Sub) simultaneously feedback continuous low-level state, and duration exceeds preset threshold, control unit will lock status and light up fault lamp, finally recording DTC C1B9C23 Master/Sub/Torque Signal Always Low Level. This process aims to prevent steering loss of control risk due to missing input signals.