meaning pointing to the "Low Side Negative Current During Bucking" abnormal event. This fault code is triggered by the on-board control unit when monitoring the working status of the power assembly, marking that during critical operating conditions where the system executes voltage conversion (bucking), the actual current direction or polarity at the low side deviates from preset logical expectations, manifesting as a "negative current" characteristic. This definition indicates that abnormal operation occurs within the on-board power assembly or its related current feedback loop in Bucking mode. The control system performs real-time verification based on preset electrical models. When an inconsistency is detected between the current signal at the physical connection point and the expected direction, the system judges it as a fault and stores this code. This is an important protective record for the on-board power management system (PMS) regarding high or medium-low voltage power conversion efficiency and safety.

Common Fault Symptoms

Based on the underlying logic of on-board power assembly failure, vehicle owners and technicians may observe the following feedback phenomena during actual vehicle operation:

• Instrument System Warning: High-voltage power or charging system related yellow/red indicator lights may illuminate on the dashboard, indicating to the driver that the vehicle is in a non-normal electrical state.
• Restricted Power Output: Due to power management strategy intervention for protection, vehicles may experience power limitation (Power Limiter) during acceleration, manifested as sluggish power response, limited torque, or reduced maximum speed.
• Electronic Device Restart: On-board low-voltage network loads (e.g., entertainment systems, air conditioning control systems) may unexpectedly reset or go black due to unstable power supply.
• Abnormal Energy Consumption Increase: Under the same operating conditions, if reverse current is detected flowing back to the high-voltage bus or Battery Management System (BMS), it may cause unpredictable fluctuations in whole vehicle energy consumption data.

Core Fault Cause Analysis

Targeting the explicitly stated "on-board power assembly failure" in the fault description, combined with general automotive diagnostic logic, the causes of this problem can be summarized into the following three core dimensions:

1. Hardware Component Failure: Primarily refers to performance degradation or physical damage of critical power devices (e.g., Bucking converter MOSFETs, inductors, or capacitors) within the on-board power assembly. This causes current unable to flow in the correct direction, or detects negative feedback current caused by component breakdown at the low side.
2. Wiring and Connector Abnormalities: Physical wiring connections between the on-board power assembly and the controller exhibit high impedance issues, such as harness wear, plug pin oxidation, or corrosion. These poor physical connections may lead to signal sampling errors, causing the controller to misjudge the current direction as negative.
3. Controller Logic Operation Errors: Although less common, algorithms within the Power Management Control Unit may experience instantaneous deviations when monitoring low-side current feedback, leading to false judgments of normal fluctuation signals and triggering fault records.

Technical Monitoring and Triggering Logic

The control unit's fault judgment algorithm performs precise timing monitoring specifically for the "Bucking" operating condition, with the logic as follows:

• Monitoring Target: The system focuses on real-time collection of feedback signals from low-side current sensors, with a core focus on the relationship between current Direction (Direction) and Duty Cycle.
• Numerical Criteria: In Bucking mode, the low side should output positive current load under normal conditions; when reverse current flow is detected (i.e., appearing as Negative Current) and duration exceeds a preset threshold, it is judged as abnormal. Although specific trigger voltage or milliampere values are not detailed here, its logic is based on absolute value comparison of current polarity (Positive/Negative).
• Specific Operating Condition Triggering: This fault activates only during Bucking conversion. The control unit filters data from stationary or charging modes, ensuring that the DTC is recorded only when reverse current is detected while the Power Management Module actively performs energy transfer (supplying to low-side loads from high side). This technical specification aims to provide structured theoretical support for professional diagnostic personnel targeting P1EC500 fault codes, ensuring accurate understanding of system current direction monitoring requirements when analyzing on-board power assembly.

cause unpredictable fluctuations in whole vehicle energy consumption data.

Core Fault Cause Analysis

Targeting the explicitly stated "on-board power assembly failure" in the fault description, combined with general automotive diagnostic logic, the causes of this problem can be summarized into the following three core dimensions:

1. Hardware Component Failure: Primarily refers to performance degradation or physical damage of critical power devices (e.g., Bucking converter MOSFETs, inductors, or capacitors) within the on-board power assembly. This causes current unable to flow in the correct direction, or detects negative feedback current caused by component breakdown at the low side.
2. Wiring and Connector Abnormalities: Physical wiring connections between the on-board power assembly and the controller exhibit high impedance issues, such as harness wear, plug pin oxidation, or corrosion. These poor physical connections may lead to signal sampling errors, causing the controller to misjudge the current direction as negative.
3. Controller Logic Operation Errors: Although less common, algorithms within the Power Management Control Unit may experience instantaneous deviations when monitoring low-side current feedback, leading to false judgments of normal fluctuation signals and triggering fault records.

Technical Monitoring and Triggering Logic

The control unit's fault judgment algorithm performs precise timing monitoring specifically for the "Bucking" operating condition, with the logic as follows:

• Monitoring Target: The system focuses on real-time collection of feedback signals from low-side current sensors, with a core focus on the relationship between current Direction (Direction) and Duty Cycle.
• Numerical Criteria: In Bucking mode, the low side should output positive current load under normal conditions; when reverse current flow is detected (i.e., appearing as Negative Current) and duration exceeds a preset threshold, it is judged as abnormal. Although specific trigger voltage or milliampere values are not detailed here, its logic is based on absolute value comparison of current polarity (Positive/Negative).
• Specific Operating Condition Triggering: This fault activates only during Bucking conversion. The control unit filters data from stationary or charging modes, ensuring that the DTC is recorded only when reverse current is detected while the Power Management Module actively performs energy transfer (supplying to low-side loads from high side). This technical specification aims to provide structured theoretical support for professional diagnostic personnel targeting P1EC500 fault codes, ensuring accurate understanding of system current direction monitoring requirements when analyzing on-board power assembly.