U015B02 - U015B02 Primary Angle_Secondary Angle Signal Duty Cycle Abnormal

Definition of Fault Depth

U015B02 (Main Angle/Secondary Angle Signal Duty Cycle Abnormality) is a critical fault code recorded within the Electric Power Steering (EPS) system or the vehicle network. This code indicates that the EPS control unit, while monitoring angle feedback signals from the steering wheel or column, has detected a deviation in the Pulse Width Modulation ratio (i.e., duty cycle) between the main and auxiliary angle signals from their calibration range. In automotive electronic architecture, angle sensors serve as core components of the position feedback loop; stability of their output signals is directly linked to the accuracy with which the system calculates driver operational intent. This fault code typically implies that physical quantity encoding signals received by the control unit fail expected logic validation, indicating an anomaly at the perception level.

Common Fault Symptoms

When EPS controller stores U015B02 without performing temporary compensation, vehicle owners may perceive the following dynamic characteristics during driving:

• Dashboard Fault Indication: The "Power Steering Warning Light" or "EPS System Fault Code" icon illuminates on the instrument cluster; in some models, the "Check Engine" light may also light up.
• Steering Feel Change: The steering wheel may experience instantaneous interruption of assist torque during rotation, requiring the driver to apply additional physical torque to complete the steering operation.
• Electronic System Interaction Anomaly: Due to loss or error in steering angle data, the vehicle's Electronic Stability Control (ESP/ESC) system may misjudge vehicle status, leading to limitations on auto start-stop functions or activation of transmission protection modes.
• Fault Light Blinking Logic: Under certain conditions, if the signal duty cycle briefly exceeds the threshold, the fault indicator light may flash intermittently, indicating a state of signal instability.

Core Fault Cause Analysis

According to diagnostic data models, triggers for U015B02 are generally attributed to hardware or logic failure across three dimensions:

• Hardware Component Failure: Physical sensing elements (e.g., Hall effect elements) within the main or auxiliary angle sensors drift internally in their characteristics, causing unstable output waveforms. This directly disrupts the linear mapping relationship between duty cycle and mechanical angle, preventing the control unit from parsing accurate steering positions.
• Wiring/Connector Faults: Harnesses connecting angle sensors exhibit open circuits, shorts, or ground interference phenomena. Abnormal impedance in signal transmission paths alters voltage characteristics at the receiving end, leading to calculated pulse width ratios (Duty Cycle) that do not meet standard definition ranges. Additionally, oxidation or loosening of connector terminals introduces contact resistance, affecting signal integrity.
• Controller Internal Faults: Logic operation errors occur in the microprocessor inside the EPS control unit when processing raw sensor data. Even with normal external wiring, abnormal ADC sampling modules or incorrect firmware validation thresholds within the controller may misjudge duty cycle anomalies, triggering U015B02.

Technical Monitoring and Trigger Logic

The EPS control unit uses specific dynamic monitoring algorithms to determine this fault; specific trigger logic elements include:

• Monitoring Target: The system continuously collects pulse width ratios of main angle signals and auxiliary angle signals on the steering shaft in real-time. Duty Cycle is defined as the ratio of high-level time to total cycle time, reflecting the physical state coding of the signal.
• Numerical Threshold Judgment: Under normal operating conditions, valid signal duty cycles should fluctuate within the standard range of $0%$~$100%$. The control unit internally presets a baseline reference range; when deviation between measured values and the standard range exceeds tolerance thresholds, it is judged as abnormal. Although specific fault codes do not provide specific voltage values, their determination is based on pulse waveform timing relationships rather than simple amplitude.
• Trigger Conditions: This fault is typically monitored during vehicle power-on self-check or dynamic steering operation processes. Once the driver rotates the steering wheel, the control unit begins comparing consistency of main and auxiliary signals; if detection finds both cannot form effective synchronous feedback (e.g., one is $0%$ while another fluctuates), and persists beyond preset time windows, the system stores U015B02 and records freeze frame data.