BYD Dolphin BMS (Battery Management System) Composition and DTC Diagnosis Guide
Fault Background
The Dolphin's Battery Management System (BMS) consists of three parts: Battery Sampling and Execution Unit (BASU), BIC, and battery sampling harness, all integrated inside the battery pack. BASU is the "brain + actuator": it is responsible for charge/discharge management, contactor control, power control, SOC/SOH calculation, as well as abnormal alarm protection, current/total voltage sampling, contactor weld detection, and leakage detection; BIC is responsible for cell voltage sampling, battery temperature sampling, and cell balancing; the sampling harness connects BASU and each BIC into a communication network. This article organizes the BMS composition, diagnostic process, and DTC system into a field guide.
System Composition and Functions
| Component | Location | Main Functions |
|---|---|---|
| BASU (Battery Sampling and Execution Unit) | Inside the battery pack PDU | Charge/discharge management, contactor control, power control, abnormal alarm and protection, SOC/SOH calculation, communication, current sampling, total voltage sampling, contactor weld detection, leakage detection |
| BIC (Battery Information Collector) | Inside the battery pack | Cell voltage sampling, battery temperature sampling, cell balancing |
| Traction battery sampling harness | Inside the battery pack | Connects BASU and BICs for communication and information exchange |
Diagnostic Process
- Pre-checks: Check the auxiliary battery voltage and the low-voltage wiring harness power supply of the vehicle; standard voltage 12~14V; if below 12V, charge, replace the battery, or repair the low-voltage harness.
- Connector confirmation: Connect all relevant connectors, put the vehicle into OK (READY) power state, and proceed with BASU DTC diagnosis.
- Handle by code: Adjust, repair, or replace components based on the DTC.
- Verification test: Re-test after repair to confirm.
DTC Classification and Interpretation
| Category | Typical DTC/Fault | Troubleshooting Direction |
|---|---|---|
| Cell sampling | P1A3721 cell voltage severely low; P1A3A22/P1A3922/P1A3B21 cell temperature generally/severely high, severely low; BIC11/12/13 voltage sampling abnormal; BIC17 temperature sampling abnormal | BIC units, sampling harness, and cell condition |
| Contactor | Negative/main/precharge contactor feedback fault; main/negative contactor weld fault; P1A4800 motor controller opens main contactor; high-side drive overcurrent; high-side short to ground/power | Contactor itself, high-side drive circuit, low-voltage supply |
| Communication | U011000 communication with motor controller fault; U029787 communication with on-board charger fault; U012200 communication with low-voltage BMS fault; U029800 communication with DC converter fault; U02A200 communication with active discharge module fault; U016400 communication with A/C fault; U023487 communication with battery heater fault | Vehicle communication harness, vehicle network, and corresponding module nodes |
| Power and protection | P1A4E00 battery pack overcurrent warning; P1AE617 low auxiliary battery voltage; P1AE400 high-voltage process terminated due to low-voltage supply abnormality; P1ADC00 front motor controller high-voltage interlock fault; P2B7B00 shunt temperature generally high; P2B7E00 shunt current sampling signal lost; P2B8000 HVSU_PACK+ voltage sampling abnormal | High-voltage circuit, shunt, low-voltage supply, and interlock chain |
| Vehicle status | Airbag ECU collision alarm; severe battery imbalance; battery heating not possible due to A/C system fault | Linked modules and balancing status |
Key Parameter Quick Reference
| Item | Reference Value/Key Point |
|---|---|
| Pre-diagnostic voltage | Auxiliary battery 12~14V; if below 12V, address first |
| Power-on condition | Connectors properly mated + vehicle in OK (READY) state |
| BASU location | Inside the battery pack PDU |
| High-side drive faults | Overcurrent / short to ground / short to power, pointing to contactor drive circuit |
| Communication faults | Prioritize checking vehicle communication harness and vehicle network |
Safety Warnings
- The BMS and traction battery pack are high-voltage systems; maintenance must be performed by certified personnel according to OEM specifications. This article is for reference only.
- Before maintenance, power down the vehicle to OFF, disconnect the service disconnect switch, and verify voltage; when disassembling the battery pack, ensure insulation protection.
- Contactor weld/feedback faults indicate the high-voltage circuit may be in an abnormal state; ensure high voltage is safely disconnected before handling.
- For collision alarm faults, first confirm the vehicle's collision status; do not power up without inspection.
Maintenance Insights
The Dolphin BMS DTC system is actually three "maps": sampling faults point to BIC and cells, contactor faults point to high-side drive and low-voltage supply, communication faults point to the vehicle network—when reading codes, first classify, then decide whether to disassemble the battery pack or check the wiring harness; the direction is completely different. Two easily overlooked points: first, "low auxiliary battery voltage" can affect a wide range of high-voltage processes (P1AE400 directly terminates the high-voltage process), so check the 12~14V threshold first; second, contactor "weld detection"—it can help you detect a failing contactor early, don't wait for a feedback fault to appear. Classify first, check low voltage first, safely disconnect high voltage first—these are the three iron rules for BMS repair.
【This article is for reference only】
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⚠️ High-voltage repairs require professional certification; this article is for technical reference only — always follow the OEM service manual.