Changan Eado EV Traction Battery Structure and Fault Repair Guide

Fault Background

The ternary lithium-ion traction battery pack of the Changan Eado EV consists of 340 cells with a nominal voltage of 3.7V each, configured as 4 parallel and 85 series, with a nominal voltage of 314.5V and rated capacity of 80Ah; the pack contains 25 modules in three series/parallel configurations (4P2S×18 / 4P5S×5 / 4P12S×2), equipped with 4 BMS units (1 master + 3 slaves)—the three slave boards collect cell voltages and temperatures for 1~32#, 33~56#, 57~85# respectively, while the master board handles total current acquisition, high-voltage interlock detection, relay control, and vehicle CAN communication. The repair section provides complete procedures for five major faults: self-check failure (safety switch→fuse→busbar <100V threshold), pre-charging failure (precharge resistor ≈52Ω), relay fault, battery insulation fault (<20MΩ threshold), high-voltage interlock open circuit (pins 13/14 continuity test). This article is compiled as a repair guide.

Battery Pack Structure and Parameters

BMS division of labor: Slave boards collect cell voltages and temperatures (segments 1~32# / 33~56# / 57~85#); the master board collects total battery current, detects high-voltage interlock, controls battery relays, and communicates with the vehicle CAN. The BCU controller in real time collects and monitors voltage/current/temperature, estimates SOC and current available power, executes overvoltage, overcurrent, overtemperature fault indications and leakage current protection, and includes CAN fault diagnosis and calibration functions.

Self-Check Failure Fault

Troubleshooting sequence:

1. Check the battery safety switch—remove the rear seat and rear seat backrest, unplug the safety switch connector assembly, and check whether the connection is reliable; if loose, unplug and reinstall;
2. Check the battery fuse—use a multimeter to test whether the fuse inside the safety switch is conductive; if not, replace the battery fuse;
3. Check the battery busbar—connect the safety switch, use a multimeter to measure the voltage between the battery total positive and total negative terminals (i.e., the voltage between the two busbars entering the high-voltage electrical box)—if <100V, check whether the busbar connections are reliable, loose, or if the busbar is broken;
4. If voltage reaches 100V but fault persists → replace the battery management controller assembly;
5. If still present → replace the signal acquisition wiring harness assembly inside the battery pack.

Pre-Charging Failure Fault

1. Check the precharge resistor—use a multimeter to measure the precharge resistor value in the high-voltage electrical box, whether it is approximately 52Ω—if not, replace the precharge resistor;
2. If resistor is normal → replace the precharge relay;
3. If fault persists → replace the battery management controller assembly;
4. Read freeze frame data—if the external total voltage of the battery reaches above 95% of the pack internal total voltage and the fault persists after replacing the controller → replace the signal acquisition wiring harness assembly inside the battery pack.

Relay Fault

1. Check the wiring harness—whether the relay control harness connections are loose or poorly connected; if so, reconnect;
2. If harness is fine → replace the battery management controller assembly;
3. If fault persists → replace the corresponding relay;
4. If still present → replace the signal acquisition wiring harness assembly inside the battery pack.

Battery Insulation Fault

Sectional measurement (using insulation tester):

1. Measure the insulation resistance between the connector terminals of the battery pack high-voltage output port (connected to high-voltage power cables) and the enclosure—if <20MΩ, the high-voltage circuit is judged to have an insulation fault: remove the battery, inspect and locate the point of unqualified insulation resistance (visually inspect for damaged insulation on busbars, or sequentially remove busbars to locate), and replace the faulty component once identified;
2. Measure the insulation between the high-voltage output port (for fast charging) connector terminals and the enclosure—same <20MΩ threshold;
3. Measure the high-voltage circuit connected to the safety switch socket—same <20MΩ threshold (visually inspect for damaged insulation on harness or busbars, sequentially remove busbars to locate);
4. If all three locations are ≥20MΩ and the vehicle still reports an insulation fault—replace the battery management controller assembly (first confirm no insulation issues with other components).

High-Voltage Interlock Loop Open Circuit Fault

1. Use a multimeter to test continuity between pins 13 and 14 of the vehicle-side low-voltage connector to the battery pack—if not continuous, first check interlock issues in other components outside the battery pack;
2. Check the high-voltage output port (main power) connector interlock terminals and the high-voltage output port (for fast charging) of the battery pack—if interlock terminals are backed out or bent, replace the corresponding high-voltage connector or harness;
3. If no abnormality → remove the battery pack, open the cover, short-circuit the high-voltage interlock loop inside the battery, and test whether the loop is continuous;
4. If still not continuous → re-plug/unplug the BMS master board connector and verify after installation—if the fault does not disappear, replace the BMS master board;
5. Use a multimeter to test continuity of each high-voltage interlock loop segment by segment, and replace the corresponding high-voltage harness once the faulty component is identified.

Key Parameter Quick Reference

Safety Warnings

• This article is for technical reference. Traction battery repair involves high-voltage work; safety disassembly training is required, and the safety switch must be disconnected and insulating gloves worn.
• Insulation fault troubleshooting requires battery disassembly and cover opening—strictly follow pack-level disassembly safety discipline (see disassembly guide), and immediately insulate exposed busbars.
• The fuse inside the safety switch must be measured with the switch disconnected; voltage measurements after connecting the safety switch must be treated as high-voltage work.
• Modules are non-serviceable; cell/module-level repair is limited to module replacement.

Repair Insights

The repair procedures for these five faults have two clear threshold main lines: voltage thresholds (self-check <100V, precharge external total voltage ≥95%) and resistance thresholds (precharge ≈52Ω, insulation <20MΩ)—each "multimeter/insulation tester reading" directly points to the next action, with no ambiguous zones. The structural parameters are also worth remembering: 4 parallel 85 series 340 cells = 314.5V, with nominal voltage exactly 3.7V×85; the slave boards divide the 85 series points into segments of 32/24/29, so "which slave board reports a code" can narrow the fault to that module segment. Three on-site details: the safety switch houses a fuse—the second step in self-check failure is to test the fuse inside the switch, a location many overlook; the interlock test point is at pins 13/14—test from the vehicle side first to split "internal pack issues" from "external pack issues" at once; BMS master board connector reseating—if the interlock loop is still not continuous after shorting, first reseat the master board connector before replacing the board, to avoid misdiagnosing a poor contact as a board-level fault. Finally, the replacement order follows a pattern: harness (cheapest) → relay/resistor (next) → battery management controller (central hub) → signal acquisition harness (final fallback), from low to high cost, which exactly matches the troubleshooting tree order.

---

【This article is for reference only】