U015A38 - U015A38 Primary_Secondary_Torque Signal Period Abnormal

U015A38 Master/Slave/Torque Signal Periodicity Irregularity - Technical Documentation

Fault Definition Depth

DTC U015A38 (Description: Master/Slave/Torque Signal Periodicity Irregularity) belongs to the Communication & Control System diagnostic category, its core points to the collaborative work logic between various control units within the Electric Power Steering System (EPS). In this system, "Master/Slave" usually represents the main electronic control unit and an auxiliary or subordinate control module, while "Torque Signal" is a critical data stream used for real-time feedback of motor physical position, rotation speed, and steering wheel angle. This fault code indicates that the diagnostic system detected deviations, interruptions, or desynchronization phenomena in the periodicity (Signal Periodicity) of torque signals during transmission.

At the engineering principle level, this reflects that the Control Unit (Control Unit) within the system failed to receive feedback signals conforming to preset timing characteristics, or the received signal period does not match the instruction period sent by the main controller. This fault directly affects the stability of the Feedback Loop (Feedback Loop), possibly leading to inaccurate power steering logic calculations, thereby affecting vehicle driving safety.

Common Fault Symptoms

Based on the system status and diagnostic logic after DTC triggering, owners or technicians can usually observe the following specific driving experience and instrument feedback characteristics:

• Dashboard Warning Light Illumination: EPS System fault indicator light (steering wheel icon) or Engine Fault Light (Check Engine Light) is continuously on or flashing, indicating the system has entered a restricted mode.
• Abnormal Steering Feel Changes: Under specific conditions (e.g., vehicle startup, turning, or low-speed crawling), drivers may feel sudden increase in steering resistance, appearing "heavy", or steering response becomes sluggish, delayed.
• Reduced Power Steering Automatic Return Capability: When torque signal period detection fails, motor drive logic may adjust assistance output, causing the steering wheel to not maintain a smooth return trend like normal state.
• Vehicle Dynamic Limit Triggers: Some system strategies, after detecting severe periodic abnormalities, may temporarily cut off assistance support under high power mode, causing vehicles to show unnatural mechanical sensation during high speed or emergency steering.

Core Fault Cause Analysis

According to raw information provided by diagnostic data, fault root causes can be attributed and analyzed from the following three technical dimensions:

• Hardware Component Level Mainly involves integrity of Torque Sensor and its integrated module. If sensor coils, magnets, or encoder discs suffer physical wear, output analog or digital pulse signal amplitude may become unstable, triggering period calculation anomalies. In addition, if Hall Elements (Hall Element) inside relevant actuators drift, it will also affect real-time position feedback signals.

• Wiring/Connector Level Corresponding to "Torque Sensor Circuit Fault" mentioned in raw data, physical connection status needs focused inspection. Including whether harness is subject to electromagnetic interference causing signal crosstalk, connector pins oxidation/looseness, wire insulation layer damaged causing ground short or open circuit. These external physical connection instabilities directly destroy signal integrity, causing calculated period data by control unit to exceed logic thresholds.

• Controller Level Corresponding to "EPS Controller Internal Fault" mentioned in raw data, this belongs to Logic Operation Unit (MCU) or Input/Output port circuit anomalies. If controller internal processing program fails software check, memory errors, or signal processing circuit hardware aging, it may cause erroneous timestamp marking or filtering of received torque signals, misjudging as period abnormalities.

Technical Monitoring & Trigger Logic

The diagnostic control unit uses dynamic monitoring mechanism to judge this fault during real-time operation, specific logic follows:

• Monitoring Target System continuously monitors stability of Signal Voltage and Torque Signal Pulse Frequency. Focus is on determining Communication Timing between Main Controller and Auxiliary/Subordinate Modules, and duty cycle of physical feedback signals. System compares deviation between currently received signal period $T$ and historical reference period $T_{ref}$; once deviation exceeds preset allowed range, it is considered abnormal.

• Specific Conditions This fault code is not static triggered but generated during dynamic monitoring while driving motor. Usually occurs when vehicle is driving and steering actions are frequent, torque load changes. When control unit attempts to read real-time feedback signals for closed-loop control, if continuous multiple detections find data stream unexpected interruption or period jitter, system immediately records fault code U015A38 and stores freeze frame data.

• Judgment Threshold Logic Although specific voltage or frequency values vary by vehicle architecture, judgment core lies in signal consistency. As long as input signal periodicity cannot meet control algorithm linearity requirements, or unexpected jumps (Signal Jumping) occur, system deems signal period untrustworthy, locking fault code to prevent potential safety risks.