Changan Plug-in Hybrid Traction Battery Assembly Diagnosis and Disassembly Guide

Fault Background

The traction battery of the Changan plug-in hybrid (777 manual) is a ternary lithium-ion assembly: 96 cells (nominal 3.65V) in series, total nominal voltage 350V, capacity 37Ah — compared to the CS15EV's 168 cells in 2 parallel 84 series (307V/140Ah), this is a 96-series pure series, higher voltage platform, smaller capacity plug-in hybrid solution. The BCU battery management system functions are the same as the CS15EV (collects and monitors voltage/current/temperature, SOC and power estimation, overvoltage/overcurrent/overtemperature alerts, leakage current protection, CAN diagnostic calibration). There are three high-voltage interfaces: IPU high-voltage power cable (F02-623000-RAKC), OBC AC slow charging cable (F02-720000-RAOC), manual service disconnect switch base (HV5-RF103-2NLA-TOI1C); low-voltage connector 1-1564526-1 (TYCO) same as CS15EV. Fault code troubleshooting uses a simpler "wiring harness → sensor/module → replace BMS → technician" five-step mode. This article is organized into a diagnostic and disassembly guide.

Sensor and Sampling Family (Five-Step Troubleshooting Mode)

After each step, use the diagnostic scan tool to clear stored/history DTCs before verifying; wiring harness issues always come before component replacement.

Cell Voltage Family (Multimeter Comparison Bisection Method)

P1B25/P1B2D cell voltage too high level 3/level 4, P1B05/P1B0B cell voltage too low level 3/level 4, P1B26 cell voltage too low share the same path:

1. Use the diagnostic scan tool to obtain battery status at fault time and current time, check the highest/lowest cell voltage values and their numbers;
2. Check the cell voltage acquisition circuit and connection harness for looseness/poor contact;
3. Use a multimeter to test the cell voltage value of the corresponding number — if inconsistent with the diagnostic scan tool reading → replace BMS (acquisition circuit fault); if consistent → replace or maintain the battery module or cell;
4. If still not eliminated → notify professional technician;
5. Clear stored/history DTCs.

Temperature and Insulation

P1B29 battery module temperature too high level 4: Use diagnostic scan tool to check highest temperature and its number → after vehicle static for 5h read current battery temperature values, the difference between each temperature value should be within 2°C — if the difference is large, replace that temperature sensor → then check the temperature connection circuit, acquisition circuit connection, and sensor installation.

P1B41 insulation fault: Use insulation megohmmeter to test insulation resistance of each high-voltage system separately — for high-voltage systems with insulation resistance <20MΩ, refer to that system's insulation fault troubleshooting method; if positioned as battery insulation problem, check whether the battery has water ingress, whether copper busbars are worn, whether high-voltage components are secured → rectify → replace BMS → technician.

Precharge / Interlock / Crash / Communication

• P1B44 precharge fault: Charging connection harness short circuit/poor connection → eliminate harness issue → replace BMS → technician;
• P1B4E battery-side high-voltage interlock: Check each high-voltage connector and its harness connection in sequence, reconnect or replace if not effectively connected → replace BMS → technician;
• Crash type (P1B2A/P1B2B): First ask whether the vehicle has been in a crash — if yes, simply clear the codes; if not, check the crash signal hardwire detection harness → replace BMS → technician;
• U1200 vehicle CAN communication reception fault / P1DEE VCU CRC / P1DEF OBC CRC / P1DF0 CMU CRC: External communication harness short circuit/poor connection → eliminate harness issue → replace BMS → technician; P1D22 EEPROM checksum fault → replace BMS.

Disassembly and Installation

Safety 8 items: ① Operators must be trained and qualified; ② Equipment must be fault-free; ③ Environment dry and clean; ④ Insulated gloves throughout; ⑤ No metal objects worn; ⑥ Battery assembly must be in disconnected state and exposed copper busbars must be insulated with insulating tape; ⑦ Parts and tools must not be placed on the battery assembly; ⑧ Small parts and standard parts must not fall into the battery assembly. Immediately insulate removed modules or copper busbars with insulating tape to avoid short circuit accidents.

Disassembly five steps: 1. Remove the safety switch (insulated gloves, disconnect power first); 2. Remove the battery pack bottom guard plate (electric screwdriver + M10 socket); 3. Disconnect connections on the battery pack — two high-voltage connectors + one low-voltage connector (electric screwdriver); 4. Disconnect the water cooling system hoses — vacuum must be drawn before adding coolant; 5. Remove the battery pack — first support the battery pack with special tooling, then remove a total of 6 fastening bolts (air wrench + M16 socket, 3 at the front and 3 at the rear).

Tools: Diagnostic scan tool, digital multimeter, insulated gloves, megohmmeter, torque wrench.

Safety Warnings

• This article is for technical reference. Traction battery inspection is high-voltage work and must be performed by trained and qualified personnel per OEM specifications, with insulated gloves throughout and no metal objects worn.
• Keep the battery assembly in disconnected state during operation, immediately insulate exposed copper busbars and removed modules/busbars with insulating tape; small parts must not fall into the battery assembly.
• Insulation troubleshooting per <20MΩ system-by-system positioning; after coolant hose removal/installation, vacuum must be drawn before adding coolant.
• High-voltage warning: The battery assembly is live with high voltage; do not operate without training.

Maintenance Insights

The difference between the plug-in hybrid battery code table and the CS15EV best illustrates "platform determines thresholds": 96-series pure series 350V/37Ah vs 2P84S 307V/140Ah — PHEV relies on the engine as backup, so capacity only needs 37Ah, but the voltage platform is higher (matching the OBC's 455V/165V output window). The troubleshooting mode in this manual is more concise: "wiring harness → sensor/module → replace BMS → technician" five-step chain runs through all codes, without as many thresholds as the CS15EV, but retains three essences: cell voltage "multimeter vs diagnostic scan tool" comparison bisection method (reading mismatch → acquisition circuit fault, replace BMS; match → cell body fault, replace module/cell) — this is the fastest way to judge "false cell faults"; temperature code's "static 5h + each point temperature difference ≤2°C"; insulation code's "<20MΩ system-by-system positioning" — first sweep all high-voltage systems with a megohmmeter, check whichever is below 20MΩ, faster than the CS15EV's segmented unplugging. Two points for disassembly: 6 M16 bolts, 3 front and 3 rear, use special tooling to support before removal; vacuum must be drawn before adding coolant — the plug-in hybrid battery water cooling circuit is sensitive to air bubbles; skipping the vacuum step will repeatedly report temperature deviation faults.

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【This article is for reference only】