BYD Tang DM-i Traction Battery Pack Pin Diagnosis and Replacement Guide

Fault Background

The Tang DM-i traction battery pack is one of the two main power sources of the vehicle, supplying power to both the drive system and all electrical loads. Its maintenance has two characteristics: first, the battery pack output connector integrates high voltage, low voltage, CAN, fast-charge contactor power supply, temperature detection, and high-voltage interlock into one connector, and the pin definitions are the map for troubleshooting; second, replacing the battery pack requires recovering the refrigerant first—this battery pack uses refrigerant-based thermal management, and the expansion valve and A/C line shields are in the removal path. This article compiles the output pins, diagnostic procedures, and the complete replacement process into a field guide.

System Overview and Output Pin Definitions

The traction battery system is one of the main power sources of DM vehicles, providing electrical energy to the drive system and other electrical loads. Electrically, the high-voltage distribution box, discharge socket, AC/DC charge port, and battery pack form the vehicle's high-voltage circuit. The main pins of the battery pack output connector are as follows:

Diagnostic Procedure

1. Check the low-voltage lithium iron battery voltage and the vehicle's low-voltage harness power supply; standard is 11~14V; if below 11V, charge or replace the starter battery, or check the vehicle's low-voltage harness;
2. Connect the connectors properly, turn the vehicle to ON, and enter battery management system (BMS) DTC diagnosis;
3. Adjust, repair, or replace components based on the fault;
4. Confirm the test.

Fault code categories for reference: AFE (front-end sampling) 1~14 operating abnormal faults, AFE voltage sampling abnormal faults (1/2/3), AFE temperature sampling abnormal faults; contactor weld faults (main contactor, negative contactor weld); communication faults with A/C; cooling system faults causing inability to heat/cool—troubleshoot one by one according to BMS DTCs.

Traction Battery Pack Replacement Procedure

If the traction battery is confirmed to have issues requiring repair, please replace the battery under manufacturer guidance, following the steps below for removal and replacement.

1. Power down: Turn vehicle to OFF → disconnect low-voltage battery negative terminal → open front hood, unplug the DC high-voltage bus connector at the front compartment motor controller end → wait 5 minutes;
2. Use a voltage measurement tool to confirm the voltage between the unplugged high-voltage bus terminals is within a safe range (less than 60V DC), and insulate the connectors with insulating tape to prevent short circuits and foreign object entry;
3. Use a refrigerant recovery machine to recover refrigerant in the front compartment (see A/C repair instructions for recovery method);
4. Raise the vehicle to a suitable height with a lift, and use special lifting equipment to support the battery pack;
5. Remove the heat shield and A/C line shields, then use special lifting equipment to support the battery pack;
6. Unplug the electronic expansion valve (EXV) control connector, remove the EXV fasteners with an Allen wrench, then pull out the EXV (take care to protect against refrigerant spray during removal);
7. Remove the DC bus connector fasteners (M6 bolts) and unplug the connector; unplug the battery information sampling communication line connector;
8. Use an 18mm socket to remove the tray perimeter fasteners and take out the traction battery pack;
9. Wearing insulating gloves, use a multimeter to test whether the new traction battery pack bus has voltage output; only install if there is no voltage output;
10. Wearing insulating gloves, place the new traction battery pack on the battery lifting equipment, and use tools for guidance during lifting to align the battery pack mounting holes;
11. Install the tray fasteners, torque to 135N·m;
12. Wearing insulating gloves, connect the electronic expansion valve;
13. Wearing insulating gloves, connect the traction battery pack DC bus connector, then the battery information sampling communication line connector;
14. Recalibrate SOC, power on to confirm no vehicle faults, then repair is complete;
15. Storage requirement: vehicle SOC 30%, if SOC<30%, charge as needed;
16. Open the front compartment and charge refrigerant (use original refrigerant provided by the manufacturer), see the A/C system repair manual for details.

Safety Warnings

• This article is for technical reference; traction battery replacement must be performed by certified personnel under manufacturer guidance. Readers unfamiliar with the procedure are strictly prohibited from performing it themselves.
• Strictly follow the power-down sequence: OFF → disconnect low-voltage negative → unplug high-voltage bus connector → wait 5 minutes → confirm <60V.
• Refrigerant recovery and charging must use specialized equipment and original refrigerant; protect against refrigerant spray when removing the EXV.
• Before installing a new battery pack, use a multimeter to confirm no voltage output on the bus; wear insulating gloves throughout; tray fastener torque 135N·m.
• After reassembly, recalibrate SOC and confirm no faults; storage SOC must not be below 30%.

Maintenance Insights

Three easily overlooked "procedural justice" points are hidden in the Tang DM-i battery pack replacement process: first, "recover refrigerant before touching anything"—the battery pack thermal management is on the refrigerant circuit; skipping thermal management and directly disassembling the pack will cause a refrigerant spray accident when the EXV is pulled; second, "test voltage on the new pack before installation"—the battery pack comes with residual voltage; installing with bus output is equivalent to live work; third, "recalibrate SOC after replacement"—SOC is the BMS's "accounting" of energy state; replacing the pack without recalibration means the instrument display and actual energy are two different accounts. Also remember two hard numbers: tray fasteners 135N·m and storage SOC 30%—torque controls safety, SOC controls battery life.

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【This article is for reference only】