BYD Yuan PLUS Traction Battery Pack Fault Diagnosis and Removal/Installation Guide

Fault Background

The Yuan PLUS traction battery pack has two notable differences from other vehicle lines: first, refrigerant direct cooling — the battery pack has coolant inlet/outlet ports, and the removal/installation procedure includes "recover refrigerant" and "remove refrigerant inlet/outlet pipes," using A/C refrigerant rather than conventional coolant; second, dual-threshold leakage determination — insulation resistance below 500Ω/V indicates general leakage, below 100Ω/V indicates severe leakage. The measurement method involves connecting a known 1MΩ measurement resistor in parallel with the battery pack assembly insulation resistance, then calculating using four voltage values. Additionally, the manual categorizes battery pack faults into 6 modes (over-temperature, SOC jump, EV function limitation, capacity calibration error, protection structure impact, others), with a unified handling approach: "pull over → contact service → remove and deliver to BYD professional repair." This article organizes fault determination, leakage measurement, and removal/installation procedures into a field guide.

Battery Pack Fault Modes and Determination

Instrument fault display forms: EV function limitation, over-temperature warning, traction battery fault. The 6 fault modes and determination points listed in the manual are as follows:

Leakage Detection: 1MΩ Parallel Resistor Dual-Threshold Method

1. Connect vehicle VDS to read data;
2. Wear insulating gloves and insulating shoes, ensure safety, then use a multimeter to measure: close the contactors, measure the voltage between the positive and negative terminals of the traction battery pack assembly and the tray respectively, define the higher as U1 and the lower as U1′; among the two corresponding insulation resistances, the one with smaller resistance is defined as the assembly insulation resistance Ri;
3. Add a known measurement resistor R0 (R0 = 1MΩ) in parallel with Ri, then measure the voltages U2 and U2′ between positive/negative terminals and the tray;
4. Substitute R0 and the four voltage values U1, U1′, U2, U2′ into the calculation formula (including correction for the internal resistance of the voltage measurement device) to find the insulation resistance R;
5. Determination: R < 500Ω/V → general battery pack leakage; R < 100Ω/V → severe battery pack leakage; after confirmation, remove the battery pack and deliver to BYD professional repair.

Removal/Installation Protection and Tools

Personnel protective equipment:

• Cloth gloves: hand protection during screw removal and item handling;
• Standard electrician insulating gloves: protection during operations at traction battery leads, service disconnect switch, and signal line connectors;
• Insulating shoes: foot protection when removing or disconnecting high-voltage components;
• Protective face shield: face protection when removing a pressure-relieved traction battery.

Operation tools:

• Lifting platform cart: height 1.2~1.4m, platform size 1800mm×800mm, lifting height not less than 1.4m, load capacity over 1000kg — to support the traction battery;
• Scissor lift platform cart: load capacity over 300kg, for lifting equipment.

Removal and Installation Procedure

Removal procedure (must be in order):

1. Remove the battery pack fixing bolts under the rear seat;
2. Lift the vehicle;
3. Remove the fender liner and ground wire in sequence;
4. Recover refrigerant;
5. Remove the battery pack refrigerant inlet/outlet pipes;
6. Disconnect high-voltage and low-voltage connectors;
7. Remove the battery pack fixing bolts;
8. Lower the battery pack.

Installation procedure: Place the traction battery pack assembly on the lifting platform or a simple support platform (assembly is heavy, pay attention to safety) → align the position so that the battery pack assembly mounting holes align with the body mounting holes → install fixing bolts, torque 135N·m.

Removal/installation precautions:

• The traction battery is a high-voltage hazardous product; parts connected by yellow lines or with high-voltage labels must not be disassembled by unauthorized personnel other than BYD authorized service store staff;
• The power output outlet socket must be covered with insulation protection to prevent foreign objects from falling in and causing electric shock;
• Sampling wires must not be pulled forcefully or bent excessively to prevent signal wire damage;
• Screw tightening torque must be applied with professional tools per design requirements; after installation, apply torque marks to fasteners;
• Pay attention to part labels to prevent omission or incorrect installation;
• Prohibit violent disassembly, dropping, collision, module tilting, intentional short circuit, and other abnormal operations; prohibit disassembly by unauthorized personnel;
• Before operation, power down the vehicle to OFF position; pay attention to high-voltage warning labels during disassembly; do not use brute force on components with locking features.

Safety Warnings

• This article is for technical reference; traction battery service must be performed by certified personnel per OEM specifications; non-professionals are strictly prohibited from disassembling the traction battery.
• The traction battery is a high-voltage component; improper operation can cause injury or death; do not touch or operate the traction battery without appropriate protective equipment.
• Leakage detection must be performed with insulating gloves and insulating shoes; after confirming R < 500Ω/V (general) or < 100Ω/V (severe), immediately stop use and return the pack for repair.
• Before removal/installation, power down to OFF position and strictly follow the procedure order; refrigerant operations require refrigerant recovery first.
• Prohibit violent disassembly, dropping, collision, module tilting, and intentional short circuit.

Maintenance Insights

The most memorable aspects of the Yuan PLUS battery pack manual are three "differences." First, refrigerant direct cooling — the removal/installation procedure includes "recover refrigerant + remove refrigerant inlet/outlet pipes," indicating this battery pack is directly cooled by A/C refrigerant; when servicing the A/C system, the battery pack circuit must be considered, unlike coolant-based models. Second, dual-threshold leakage — 500Ω/V for general leakage, 100Ω/V for severe leakage; during severe leakage, the vehicle actively limits discharge power and illuminates the EV function limitation alarm, so "EV function limitation" should first be investigated for leakage. Third, the 1MΩ parallel method — the measurement resistor is fixed at R0 = 1MΩ, connected in parallel with the assembly insulation resistance, then four voltages (U1/U1′/U2/U2′) are measured and substituted into the formula with correction for the voltage measurement device internal resistance; the smaller of the two insulation resistances is taken as the assembly insulation resistance — missing this detail could turn severe leakage into general leakage. For removal/installation, remember one set of numbers: first remove bolts under the rear seat, lifting platform 1.2~1.4m/1800×800mm/1000kg, fixing bolts 135N·m, apply torque marks after installation.

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【This article is for reference only】