P157216 Fault Code Analysis: Low DC-Side Voltage

Definition of Fault Depth

P157216 fault code indicates abnormal monitoring of DC-side voltage in the On-Board Charger (OBC). In EV high-voltage architecture, OBC converts AC grid power to DC for Battery Management System (BMS) requirements. The core of this fault lies in the Control Unit's (ECU) failure to monitor the LLC resonant stage rear end and PFC rectifier stage rear end voltage in real-time.

When the system detects that the DC bus voltage cannot be maintained within the normal operating range, a safety strategy is triggered, leading to restricted charging function. This definition emphasizes the direct correlation between high-voltage physical parameters and controller logic determination, aiming to diagnose the integrity of the power transmission link via voltage feedback loop. Specifically, this fault involves measuring key node potentials inside the OBC, ensuring energy conversion efficiency and safe isolation during the charging process.

Common Fault Symptoms

When P157216 fault code is activated, users and vehicle diagnostic systems can observe the following phenomena:

• Charging Interrupted: Vehicle completely unable to accept external DC charging signal; charging pile cannot establish connection or disconnects immediately after connection.
• Discharge Function Limited: For models equipped with power supply capabilities, the DC power output by OBC is blocked, unable to perform discharging operations.
• Dashboard Warning: Dashboard may display "Check High-Voltage Battery System", "Unable to Charge" or specific fault indicator lights turn on.
• Charging Stop: During charging process, if voltage fluctuation reaches the judgment threshold, charging session will be forced terminated and cannot be restarted.

Core Fault Cause Analysis

According to original data records, causes of P157216 can be strictly classified into the following three hardware and logic dimensions, do not fabricate maintenance plans:

1. Hardware Component Failure

   • High-Voltage Fuse: The fusible element responsible for protecting high-voltage circuit from overcurrent damage undergoes physical fuse breakage or poor contact, causing DC loop open circuit. Original data explicitly pointed out "High-Voltage Fuse Fault" directly cutting off the power transmission path.
   • Inside On-Board Charger: Power devices (such as IGBT, MOSFET) or core components like rectifier bridge inside OBC module are damaged, resulting in abnormal voltage conversion stage, known as "Internal On-Board Charger Fault".

2. Wiring and Connector Connection Anomalies

   • Although original data did not list it explicitly, combined with Control Unit principles, high-voltage busbar fracture, sensor signal line open circuit or DC side wiring terminal oxidation loosening will lead to control unit reading voltage value lower than actual value or unable to maintain effective loop.

3. Controller Logic Operation and Calibration

   • Voltage sampling module fault or calibration parameter deviation inside On-Board Charger Controller (OBC Controller) leads to system misjudging voltage below standard, thus generating erroneous safety instructions.

Technical Monitoring and Trigger Logic

Judgment of this fault code is based on strict timing monitoring logic, ensuring dual verification of voltage thresholds under specific electrical conditions:

• Monitoring Target: System real-time monitors key node voltages in OBC power stage, specifically including LLC (Inductor-Capacitor Resonant Converter) rear end DC side voltage, and PFC (Power Factor Corrector) rear end DC side voltage.
• Condition One (Pre-Charge State): Before vehicle enters charging startup process (before charging start), if Control Unit detects LLC rear end voltage below system set safety lower limit, marked as abnormal.
• Condition Two (Load Running State): After charging program formally opens (after starting charge), if PFC rear end voltage continues to drop or falls below specified threshold, system immediately determines there is serious voltage drop risk.
• Trigger Condition: This logic is only effective under vehicle in DC Charging State. When system confirms entering charging mode, and continuously detects either of above voltage conditions not satisfied, immediately generates fault code P157216, and cuts off related high-voltage output to protect battery pack and charger hardware.