NIO ES8 Traction Battery Pack and High-Voltage System Repair Guide

Fault Background

The NIO ES8's traction battery pack is a swappable battery system: mounted under the vehicle chassis, it is secured by 10 mounting points—8 M18 bayonet bolts (front/rear and side rails) + 2 M10 bolts (through the pack interior)—with 2 Φ30 locating holes for quick and accurate installation, and 4 Φ12 lifting holes on the side rails for transport. The swap interface (electrical connectors + water hose quick couplers) achieves IP67 protection rating, and the housing seal meets high-pressure water jet/high-temperature steam wash standard IP6K9K. The pack contains 32 basic battery modules in series/parallel; the high-voltage circuit consists of relays, fuses, busbars, shunt, and swap connectors. The swap bolt torque discipline is two-stage: first pre-tighten all to 50 N·m in sequence, then final-tighten to 110 N·m in the illustrated order. On the diagnostic side, there are two families of CSD (battery monitoring circuit) communication codes: U2195~U21A4 (message counter parameter error, go to equipotential test) and U21A5~U21B4 (message checksum parameter error, go to insulation test). This article organizes the battery pack structure, swap removal/installation, testing procedures, and high-voltage safety into a reference guide.

Battery Pack Structure and Swap Interface

Swap Removal/Installation Torque

Removal: Use a wrench with the bolt socket mechanism on the special tool, loosen the 8 battery pack swap bolts around the perimeter and ensure they are fully released (operate with the battery pack removal/installation lifting and positioning tool).

Installation: Use a torque wrench with the battery pack removal/installation lifting and positioning tool, pre-tighten the 8 swap bolts in sequence to 50 N·m → then final-tighten to 110 N·m in the illustrated order.

Equipotential Test and Insulation Test

Pre-diagnostic steps (common to both code families): Vehicle in park → first disconnect the emergency disconnect switch, then disconnect the 12V battery negative terminal, wait 5 minutes → reconnect the 12V negative terminal → vehicle in "driver present" state → connect NIO Diagnostic System II (BD2) → check BMS fault codes.

• U2195~U21A4 (CSD battery pack 00~15 communication message counter parameter error) → equipotential test: If fault code still sets → return to factory for internal wiring harness inspection → replace traction battery pack assembly → clear codes with BD2 and confirm no re-set;
• U21A5~U21B4 (CSD battery pack 00~15 communication message checksum parameter error) → insulation test: Return to factory to inspect CSC Internal CAN network → replace traction battery pack assembly → clear codes with BD2 and confirm;
• After repair, additionally set up traction battery pack equipotential test (post-repair) and insulation test (post-repair) special items; these must be performed after reassembly.

High-Voltage Integrated Components and High-Voltage Safety

High-Voltage Integrated Component (HVIC) Replacement: Disconnect the AC charging socket assembly high-voltage wiring harness connector → disconnect the main wiring harness connector → loosen the clamps and disconnect the two water hose connections → remove the high-voltage integrated component.

High-Voltage Safety Points:

• High-voltage system components: high-voltage distribution unit (PDU), high-voltage integrated component (HVIC), pyrotechnic disconnect switch, etc.;
• Pre-charge circuit: precharge relay + precharge resistor in parallel with the main positive relay—at charging start, the precharge relay closes first, current flows through the precharge resistor; after current stabilizes, the main relay closes, connecting the battery pack high-voltage system to the vehicle high-voltage (protects the main relay from high-current welding);
• Collision protection: In the event of a collision, the system automatically opens the high-voltage relays; after a collision, the high-voltage system is not allowed to be re-enabled;
• High-voltage interlock (HVIL): monitors the integrity of high-voltage connectors.

Safety Warnings

• This article is for technical reference; traction battery and high-voltage system service must be performed by certified high-voltage technicians per OEM specifications. Unfamiliar readers are strictly prohibited from performing operations themselves.
• Before any diagnosis or removal/installation: disconnect emergency disconnect switch → disconnect 12V negative terminal → wait 5 minutes, sequence must not be reversed.
• Swap bolts use two-stage torque (50 N·m pre-tighten → 110 N·m final-tighten), must use a torque wrench and follow the illustrated order.
• After a collision, the high-voltage system is not allowed to be re-enabled; follow post-collision service procedures.
• Pyrotechnic disconnect switch and swap connectors involve high voltage and high current; unauthorized disassembly is prohibited.

Service Insights

The most unique aspect of the NIO ES8 battery pack manual is the "swap mindset": the battery pack is both a high-voltage component and a replaceable "part"—so the service approach is very clear: the final countermeasure for both CSD communication code families (U2195 series counter errors, U21A5 series checksum errors) is "return to factory for internal wiring harness/CSC CAN network inspection + replace battery pack assembly"; the dealership performs testing, diagnosis, and complete replacement, not pack-level repair. This brings two on-site disciplines: first, the power-down sequence—emergency disconnect switch → 12V negative terminal → wait 5 minutes; the swappable battery's power-down path has an extra emergency disconnect switch compared to a normal battery; second, two-stage torque—the 8 swap bolts are pre-tightened to 50 N·m then final-tightened to 110 N·m, must follow the illustrated order; this is the basis for battery pack-to-body alignment accuracy and safety. For high-voltage safety, remember two phrases: pre-charge first, main positive after (close the main relay only after current stabilizes to prevent welding); collision locks out high voltage (system not allowed to re-enable).

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【This article is for reference only】