U016002 Primary/Secondary/Primary + Secondary Torque Signal Duty Cycle Abnormality Diagnostic Technical Document

Fault Depth Definition

U016002 fault code belongs to the powertrain or steering system control network, its core monitoring object is key sensing data within the EPS (Electric Power Steering) system. This specific DTC refers to Primary/Secondary/Primary + Secondary Torque Signal Duty Cycle Abnormality. In vehicle electronic architecture, the EPS control unit needs high-precision physical feedback to determine driver steering force and direction. This fault definition indicates that the duty cycle (Duty Cycle) parameters calculated from raw electrical signals received by the Control Unit (ECU) do not match the actual expected values.

Here, the signal architecture adopts a redundant design, including:

1. Primary Channel Signal: Primary Torque Signal, used to provide real-time feedback on motor and steering column physical position and rotation speed baseline.
2. Secondary/Sub Torque Signal: As a safety redundancy, it provides backup data when the primary signal fails.
3. Composite Signal (Primary + Secondary): Used to verify consistency logic between the two sensors.

When the system detects that the pulse width ratio of any of the above signal channels exceeds the preset tolerance range, the fault code is triggered, indicating logical or physical deviation in the signal closed-loop feedback of the steering assist system.

Common Failure Symptoms

When U016002 fault code is stored inside the control unit, vehicle owners and vehicle monitoring systems usually exhibit the following perceptible phenomena:

• Dashboard Warning Lights On: The EPS Fault Light (or Steering System Warning Icon) in the steering wheel area stays on, indicating the assist system enters protection mode.
• Assist Torque Response Lag: When drivers turn the steering wheel, they may feel an instant increase in operating resistance or a "stuck" feeling of uneven assist force.
• System Enters Limited Mode: For safety strategies, the EPS controller may limit motor output power, causing heavy steering feel (Limp Home Mode).
• Intermittent Communication Interruption: Under specific driving conditions (e.g., turning corners, sharp turns), the fault may temporarily disappear and reappear, accompanied by signal jumps in data streams.

Core Fault Cause Analysis

Based on diagnostic logic and hardware architecture analysis, this fault is mainly caused by physical or logical anomalies in the following three dimensions, strictly prohibit blind replacement without diagnosis:

1. Hardware Components (Torque Sensor)

• Sensor Internal Component Aging: Hall elements or potentiometers inside the torque sensor drift, leading to distortion of output raw pulse width ratios.
• Signal Source Physical Damage: Core sensing units of primary or secondary sensors fail characteristics due to vibration, high temperature, unable to generate electrical signals conforming to duty cycle specifications.

2. Wiring and Connectors (Physical Connection)

• Torque Sensor Wiring Fault: This is a high-frequency hardware cause, including power line open circuit, poor grounding, or signal transmission lines subject to interference (EMI). High line resistance can cause attenuation or fluctuation of received duty cycle values at the receiving end.
• Connector Contact Oxidation: EPS controller and sensor connector terminals appear loose, corroded, or intermittent connection, causing unstable signal voltage, resulting in being judged as logical anomaly.

3. Controller (EPS Control Unit)

• Internal Fault of EPS Controller: Analog-to-Digital Converter (ADC) sampling circuit fault inside control unit, or microprocessor algorithm verification logic error processing duty cycle data, resulting in inability to correctly parse sensor data.
• Loss of Internal Calibration Parameters: Adaptive learning values of control unit are chaotic, leading to baseline shift when judging "abnormality".

Technical Monitoring and Trigger Logic

The system processes signal streams via the diagnostic monitoring module inside the EPS Controller, specific fault judgment mechanism is as follows:

• Monitoring Target: Torque Signal Duty Cycle.

  • The system continuously monitors the ratio of pulse signal width to period from primary and secondary channels.
  • Logic core lies in comparing calculated duty cycle ratio with preset sensor calibration range.

• Value Threshold Judgment:

  • Fault trigger is based on comparison of real-time collected signal value $D_{calc}$ with standard reference value $D_{ref}$.
  • When system detects difference between two input channel duty cycles exceeds internal preset tolerance limits, or primary + secondary composite signal logic verification does not satisfy consistency condition, abnormality is judged.
  • Note: Specific voltage and current thresholds are solidified by OEM (Original Equipment Manufacturer) in control unit calibration program, not directly disclosed in generic fault code definition, maintenance end needs to confirm specific parameter range based on Service Bulletin (TSB) for specific vehicle models.

• Operating Condition Dependence:

  • This monitoring is activated only during drive motor running period or when steering operation has valid input. If engine is not started or EPS is in power-off protection mode, system will not continuously report duty cycle abnormality data streams.
  • Fault code storage usually requires meeting dynamic driving cycle (Driving Cycle), i.e., signal deviation must be continuously monitored under specific vehicle speed and steering wheel angular rate to turn on fault light and record DTC.