BYD Yuan PLUS Unable to AC Charge: High-Voltage Interlock Connector Inspection

Fault Background

The Yuan PLUS uses a highly integrated eight-in-one electric drive assembly, with the on-board charger (OBC) function for AC charging also integrated within it. The high-voltage interlock (HVIL) is responsible for confirming that all high-voltage connectors are fully seated before power-up and charging. Its status is determined by the integrated smart front drive, and there is no separate low-voltage interlock wiring harness—the interlock status directly depends on the mechanical latch of the high-voltage connectors. Once a high-voltage plug is not fully seated, the system will refuse to charge. This article dissects a case of "instrument prompts to check on-board charger, unable to AC charge," where the fault point was simply a high-voltage plug that was not fully seated.

Fault Symptom

Cause Analysis

1. Integrated smart front drive fault—abnormal interlock determination inside the eight-in-one assembly.
2. Traction battery fault—abnormal high-voltage connection or internal interlock at the battery end.
3. Wiring harness fault—issue with the high-voltage wiring harness connector.
4. High-voltage interlock fault—a high-voltage connector is not fully seated, causing the interlock circuit to open.

Diagnostic Procedure

1. Read DTC to confirm: Use VDS to read the fault; the on-board charger reports P151100 "AC-side high-voltage interlock fault" as a current fault, and there is no software update available—first rule out software factors.
2. Clear and retest: Clear the DTC, then plug in the charging gun and test; the fault persists—confirming a real hardware interlock issue.
3. Understand the interlock structure: In the eight-in-one model, the high-voltage interlock is determined by the integrated smart front drive. There are two locations with mechanical interlock on the vehicle: ① the connection between the integrated smart front drive and the AC charging cable; ② the connection between the integrated smart front drive and the traction battery.
4. Inspect each location: Focus on checking the seating status of the two high-voltage connectors. When checking the multi-in-one side, it was found that the AC charging port connector was not fully seated.
5. Restore the connection: Re-seat the AC port connector fully, ensuring the latch is locked.
6. Verify and resolve: Clear the DTC, plug in the charging gun and test; charging returns to normal, and the fault is resolved.

Repair Plan

1. When encountering a "high-voltage interlock fault," first clear the DTC and retest to distinguish between a real interlock issue and an intermittent false alarm.
2. Be familiar with the eight-in-one architecture: the interlock is determined by the integrated smart front drive, and the mechanical interlock points are concentrated at two high-voltage connection locations.
3. Inspect each connector to ensure it is fully seated and the latch is locked; preliminary troubleshooting can be done without disassembly.
4. After restoring the connection, always clear the DTC and perform a full charging verification to confirm the fault does not recur.

Key Parameter Quick Reference

Safety Warning

• A high-voltage interlock fault indicates the system is in a protective state. Before inspecting connectors, the vehicle must be powered down and the charging gun unplugged.
• Do not plug or unplug high-voltage connectors while energized to avoid arcing and damaging terminals.
• After restoring the connection, ensure the latch clicks into place and perform a pull-back test to prevent delivering the vehicle with a half-seated connector.

Repair Insights

The eight-in-one high integration brings a counterintuitive conclusion: the high-voltage interlock has no independent low-voltage wiring harness; the interlock itself is the mechanical state of the high-voltage plug. So when encountering interlock faults like P151100, don't rush to suspect the controller or wiring harness. Go back to the most basic check—whether every high-voltage connector is truly seated and locked. The more integrated the vehicle, the easier it is to be stumped by a "simple problem": a plug not pushed all the way in can make the entire vehicle refuse to charge.

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【This article is for reference only】