Technical Analysis of P157016 AC Side Voltage Low Fault

In-Depth Fault Definition

P157016 (AC Side Voltage Low) is a core fault code of the internal monitoring system within the On-Board Charger (OBC) Control Unit. In the vehicle energy management system, this control unit is responsible for real-time monitoring of energy transmission quality on both the high-voltage side and the grid side. When the system is under AC charging conditions, the control unit will accurately measure electrical parameters at the input end. If the AC side voltage signal is detected to be continuously below the safety protection threshold, the system will determine it as an "AC Side Voltage Low" abnormal state. This fault definition aims to ensure the operating safety of the On-Board Charger (OBC) in a high-voltage environment, prevent energy transmission risks caused by grid fluctuations or equipment failures, and ensure the vehicle can correctly identify and isolate unstable charging input sources.

Common Fault Symptoms

• System Warning Illuminated: The dashboard or Driver Information Center (DIC) screen will explicitly display the prompt "Please Check On-Board Charging System", accompanied by a constant fault indicator light.
• Charging Function Interrupted: The vehicle cannot enter the AC charging state; even when connected to an EV charging station, it displays no current output or a frozen charging process.
• Interface Feedback Abnormal: The on-board multimedia terminal may be unable to read normal charging power data, or the State of Charge (SOC) estimation interruption occurs.

Core Fault Cause Analysis

According to the fault mechanism and system architecture, the P157016 fault usually stems from potential issues across the following three dimensions:

• Hardware Component Failure:

  • High-voltage components have insulation damage causing leakage, leading to a reduction in the effective AC side voltage.
  • External AC charging equipment (EV Charging Station) itself has abnormal output voltage or damaged internal modules.
  • Poor internal contact of the charging port assembly, burnt terminals or mechanical jamming causes signal read distortion.
  • Internal high-voltage circuit components of the on-board power assembly are aged or shorted, unable to maintain normal voltage levels.

• Wiring and Connector Connections:

  • The physical connection at the charging interface is loose, oxidized, or dampened, causing increased impedance.
  • The insulation layer of the high-voltage harness from the grid input to the control unit is damaged, causing a ground leakage signal.
  • Connector terminal pins are bent or corroded, causing excessive contact resistance on the voltage sampling lines.

• Controller Logic Operation:

  • Internal control chip (MCU) of the on-board power assembly exhibits logic drift, misjudging normal input as a low voltage fault.
  • Internal control algorithm fails to correctly filter momentary grid surge interference, erroneously generating fault signals.
  • Control unit software calibration data is abnormal, causing the threshold comparison logic to fail.

Technical Monitoring and Trigger Logic

The system dynamically scans AC side voltage via a high-frequency sampling circuit, and its judgment mechanism follows these technical standards:

• Monitoring Target: Focuses on the real-time voltage waveform stability and amplitude of the AC input side (AC Side).
• Numerical Range Judgment: The hard condition for fault occurrence is $V_{AC} < \text{specified threshold}$; that is, when the system detects the AC side voltage signal value below the internal stored standard threshold, it is recognized as a low-voltage abnormality.
• Trigger Condition Requirement: This monitoring logic is only activated when the vehicle is in an "AC Charging State". If the vehicle is parked or in DC charging mode, this DTC will not be recorded.
• Judgment Execution Timing: Once continuous sampling during the charging process meets the voltage condition $V_{AC} < \text{specified threshold}$, the control unit will immediately generate fault code P157016 and trigger the corresponding system protection strategies.