BYD Qin PLUS EV Traction Battery System: Fault Diagnosis and Removal/Installation Specifications

Fault Background

The Qin PLUS EV's traction battery system supplies all electrical energy for the entire vehicle: rated total voltage 434.4V, total capacity 56.4kWh, consisting of battery modules, battery information collectors, series wiring, tray, sealing ring, and battery sampling wires, arranged under the vehicle floor. As a high-voltage core component, its fault diagnosis and removal/installation have strict specifications—this article compiles the fault mode diagnosis methods (over-temperature/SOC jump/leakage/capacity calibration error/collision damage) and removal/installation key points from the OEM manual into an actionable guide.

System Overview

Fault Mode Diagnosis

1. Battery Pack Over-Temperature

• Two causes: ① Sensor fault leading to distorted signal acquisition; ② Excessive internal resistance in the battery pack, causing abnormal heat generation during charge/discharge.
• Symptom: Instrument cluster reports "Battery Pack Over-Temperature Fault".
• Action: Pull over immediately, contact service personnel; ultimately remove the battery pack and send it to BYD for professional inspection.

2. Battery Pack SOC Jump

• Mechanism: One or several cells in the battery pack are faulty, pulling down the voltage of individual cells; the vehicle corrects SOC based on voltage, causing SOC jumps and the driving range to automatically adjust to the range corresponding to the current SOC.
• Action: Pull over immediately, contact service personnel; remove the battery pack and send it for professional inspection.

3. Battery Pack Leakage (Key Measurement Method)

• Classification: General leakage / Severe leakage (in severe cases, the vehicle automatically cuts off power for protection).
• Measurement Method (wear insulating gloves and insulating shoes, use a multimeter):

1. Measure the voltage between the positive and negative terminals of the traction battery pack and the tray; record the higher as U₁ and the lower as U₁′; among the two corresponding insulation resistances, the smaller one is determined as the insulation resistance Ri;
2. Connect a known measuring resistor R₀ (1MΩ) in parallel, then measure the two voltages U₂ and U₂′;
3. Substitute the four voltage values and R₀ into the insulation resistance calculation formula to find Ri.

• Thresholds: Insulation resistance <500Ω/V indicates general leakage; <100Ω/V indicates severe leakage.
• Action: Remove the battery pack and send it to BYD for professional inspection.

4. Capacity Calibration Error

• Symptom: Manual calibration error causes driving range to not match current SOC; in severe cases, range jumps, and the driver misjudges range, leading to breakdown.
• Calibration Procedure (choose one):

a. If conditions allow: Use a charging cabinet to discharge until the vehicle automatically cuts off power → charge to SOC 100%, and at approximately SOC 90%, connect to the upper computer via the front compartment powertrain CAN port, open the battery management controller monitoring system, recalibrate the full charge capacity into the battery management controller at SOC 100%, and restore power;
b. If conditions are unavailable: At low SOC, enable PTC heating to discharge until power automatically cuts off, then charge to 100%, and similarly at around 90% SOC, use the upper computer via the CAN port to recalibrate capacity;
c. The battery management controller has a built-in repair function: after multiple charge/discharge cycles, it can automatically correct the capacity to near the actual value (but during this period, the driver may misjudge range and break down).

5. Protective Structure or Battery Pack Collision

• Inspection: Use a diagnostic scan tool to read battery management controller data, confirm voltage/current and warnings; inspect the extent of impact.
• Action: If the anti-scratch shield is damaged→replace the part; if the battery pack tray is severely deformed→remove the battery pack and send it for professional inspection.

Removal/Installation Specifications

Key Precautions:

• Yellow-lined connection points or components with high-voltage labels must not be disassembled by unauthorized service personnel;
• The traction battery power output socket must be insulated and covered to prevent foreign objects from falling in and causing electric shock;
• Sampling wires must not be pulled forcefully or bent excessively;
• Screw tightening torque must follow design values and use professional tools; battery pack mounting bolt torque 135N·m;
• Clean dust and contaminants from the power copper busbar and module connection points before assembly;
• Mark components during removal/installation, and apply torque marks to fasteners after completion;
• Prohibit violent disassembly, dropping, impact, module tilting, short circuits, and other abnormal operations.

Removal Procedure: Remove the battery pack inlet/outlet water pipes and collect coolant → power down the vehicle to OFF → follow the sequence for removal (do not use excessive force on fasteners) → pay attention to high-voltage warning labels and take protective measures throughout.
Installation Procedure: Place the battery pack on the lifting platform (heavy, pay attention to safety) → align mounting holes with body holes → install mounting bolts (135N·m) → connect low-voltage connectors, high-voltage connectors, inlet/outlet water pipes, and wiring harnesses in sequence.

Key Parameter Quick Reference

Safety Warnings

• The traction battery is a high-voltage component (434.4V); all measurements and removal/installation must be performed by certified personnel at authorized service centers. This article is for reference only.
• When measuring leakage, wear insulating gloves and insulating shoes; power down the vehicle to OFF before removal/installation.
• If the battery pack experiences over-temperature/leakage/SOC jump, first pull over safely, then contact service; do not continue driving.
• When lifting the battery pack, pay attention to load capacity and center of gravity to prevent falling and injury.

Maintenance Insights

The most valuable part of battery pack fault diagnosis is the two-tier leakage thresholds: the difference between 500Ω/V and 100Ω/V determines two completely different handling levels—"general leakage" and "severe leakage". During measurement, the four voltage readings plus the 1MΩ parallel resistor are indispensable. Two other lessons: First, don't just blame the instrument cluster for SOC jumps—the root cause is often a cell voltage being pulled down, and the vehicle is "correcting" rather than "jumping randomly"; Second, capacity calibration must seize the 90% window—if you miss the upper computer recalibration opportunity at SOC≈90%, you can only rely on multiple charge/discharge cycles for the controller to slowly self-repair. When repairing a battery pack, first learn to read its warning language.

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【This article is for reference only】