P157B00 - P157B00 AC Side Overcurrent

Definition of Fault Depth

P157B00 (AC Side Overcurrent) is a critical protective fault code in the On-Board Charger system (On-Board Charger, OBC), marking an unintended current load state detected by the control unit at the AC input. The core function of this fault code lies in monitoring the stability of the AC/PMS (Power Management System), preventing damage to power electronic components or the Battery Management System (BMS) due to current overload. When the vehicle is in the energy acquisition mode, the AC side overcurrent logic intervenes to ensure the onboard charger operates within safe working boundaries. This definition involves precise feedback monitoring of the core variable—the input side electrical power flow—beyond real-time physical position and rotational speed, serving as critical diagnostic data to guarantee high-voltage system integrity.

Common Fault Symptoms

After P157B00 fault is activated and written into the diagnostic memory, owners will observe the following significant abnormalities in driving experience or vehicle status indicators:

• Unable to Charge: The vehicle cannot normally initiate the charging process after plugging in the AC charging gun and connecting to a charging pile; the charging indicator light either does not turn on or remains off.
• Energy Transmission Interruption: The vehicle power management system prohibits the battery from accepting external grid energy input, leading to the termination of energy replenishment behavior.
• Instrument Panel Fault Prompt: The central display or dashboard may display "Charging System Fault" or related power limit warnings, explicitly indicating abnormalities on the AC input side.

Core Fault Cause Analysis

According to technical diagnostic logic, the causes of P157B00 must be systematically investigated from three dimensions: hardware components, wiring connections, and control strategies:

• Hardware Components (Internal to On-Board Charger): This dimension corresponds to "On-Board Charger Internal Fault" in the original data. It may involve physical damage to components such as the rectifier bridge, power IGBT modules, or AC input circuit components inside the OBC, leading to current sampling deviation or excessive actual load.
• Power Infrastructure (Charging Power Supply): This dimension corresponds to "Charging Power Supply Fault". This includes abnormal output from external charging piles, transient overcurrent caused by grid voltage fluctuations, or high impedance at connection points on the power supply cable; all these belong to hardware problems in the external power supply side.
• Controller Logic Operation: The vehicle's internal high-voltage control unit is responsible for executing protection algorithms. If the controller's current sampling circuit deviates or there are deviations in threshold judgment logic, it may incorrectly trigger overcurrent protection, resulting in fault code generation.

Technical Monitoring and Trigger Logic

The determination of this fault code strictly follows preset electrical parameter logic. When the system executes fault judgment, it relies on the following monitoring targets and working conditions:

• Monitoring Target: The onboard charging controller continuously monitors the AC side input current ($I_{AC}$) signal in real time, focusing on analyzing the duty cycle and instantaneous amplitude of the signal.
• Trigger Logic Condition: The fault is effective only when triggered under "Vehicle AC Charging State". When the system detects that the AC side current value exceeds the specified threshold (set as $I > \text{specified threshold}$), it judges that the overcurrent protection condition is met.
• Diagnostic Status Definition: Once the instantaneous current value $I_{AC}$ monitored at the current moment is greater than the specified protection upper limit threshold, the system will immediately record the fault frame and generate P157B00 DTC, while executing hardware protection strategies (cutting off the charging circuit) in accordance with the set fault conditions.