Geometry C Traction Battery System DTC Thresholds and Replacement Guide

Fault Background

The Geometry C's traction battery is a ternary lithium battery: lithium cobalt oxide, lithium manganese oxide, or nickel-cobalt-manganese compounds as the cathode, carbon materials that can embed lithium ions as the anode, using an organic electrolyte. The battery pack consists of a module assembly, CSC acquisition system, battery control unit (BMS) integrated inside the pack, and high-voltage distribution unit (B-BOX). This system has high diagnostic density—DTC trigger conditions are precise to temperature windows and voltage thresholds (temperature difference ≥25°C for 60s, insulation resistance <500Ω/V for 20s), and thermal runaway determination has 14 combined conditions. This article organizes the system composition, DTC trigger conditions, diagnostic procedures, and replacement torque values into a field guide.

System Overview and Composition

BMS functions: real-time monitoring of the traction battery pack's total voltage, total current, temperature at each measurement point, and individual cell voltage, performing fault diagnosis, SOC (state of charge) calculation, short-circuit protection, leakage monitoring, alarm display, charge/discharge mode selection; and reporting traction battery parameters to the VCU, which controls the charging and discharging power of the traction battery.

DTC List and Key Trigger Conditions

Thermal runaway determination (report if any condition is met): Vmin<2.1V (0.5s) and Tmax>67°C (2s); Vmin<2.1V and dT/dt>3°C/s; Vmin<2.1V and temperature difference >30°C; voltage sampling open circuit fault count ≥1 (5s) and Tmax>67°C / dT/dt>3°C/s / temperature difference >30°C / all NTCs in same module failed (20s); (FPC+HVIL) open circuit signal combined with the above conditions, combined with Vmin<2.1V, combined with voltage sampling open circuit, combined with CSC communication loss, etc.

Diagnostic Procedure

General approach (BMS-type faults):

1. Use diagnostic scan tool to confirm the DTC is stored again: road test in READY mode for at least 10 minutes before reading codes;
2. Visual inspection of BMS (damage, deformation, contamination, looseness) and wiring harness connectors;
3. Reprogram and configure the BMS, confirm system is normal;
4. If still abnormal, check BMS power supply and ground wiring harness;
5. Replace BMS, reprogram and configure again;
6. Clear DTCs, road test for at least 10 minutes, confirm no DTC output.

Special procedure for DC charging port faults (e.g., P159C00 internal/external voltage difference greater than a certain value, DC charging pre-charge relay closed for 500ms): preliminary inspection of DC charging socket and BMS → check wiring harness between them for open circuit—in OFF state, disconnect DC charging socket wiring harness connector BV20 and BMS module wiring harness connectors CA69, CA70, use multimeter to measure each terminal according to the table, if not compliant, repair or replace the wiring harness.

Traction Battery Assembly Replacement

Removal (wear insulating gloves throughout):

1. Disconnect the battery negative cable;
2. Lift the vehicle, disconnect the DC bus assembly (traction battery side);
3. Drain the traction battery coolant;
4. Remove the power wiring harness cover assembly and battery bottom guard plate;
5. Place a platform cart under the vehicle to support the traction battery assembly;
6. Unclip the traction battery inlet and outlet water pipe clamps and pull off—place a waste fluid container at the connection before pulling the pipes to prevent coolant splashing;
7. Remove 1 fixing bolt for the traction battery ground wire;
8. Disconnect front compartment wiring harness connector 2 and traction battery high-voltage wiring harness connector 3;
9. Remove 3 fixing bolts for the rear mounting bracket of the traction battery pack and 18 fixing bolts at the bottom;
10. Slowly lower the platform cart to remove the battery assembly—during lowering, move the platform cart slowly forward to avoid interference between the battery and rear suspension.

Installation: 18 bottom fixing bolts 78N·m; 3 rear mounting bracket bolts 78N·m; ground wire fixing bolt 9N·m; connect high-voltage wiring harness connector 3 and front compartment wiring harness connector 2; during raising, move the platform cart slowly backward to avoid interference with the body; finally add coolant, connect DC bus (traction battery side) and battery negative cable.

BMS and High-Voltage Box Replacement

BMS Replacement: disconnect negative → disconnect DC bus (traction battery side) → drain coolant → remove fuse → disconnect BMS wiring harness connector → remove 4 fixing bolts (10N·m) → take out BMS. Installation in reverse order: BMS 4 bolts 10N·m → connect wiring harness → install fuse → add coolant → connect DC bus → connect negative.

High-Voltage Box Replacement: internal operations must wear insulating protective gloves, wrap wiring harness connectors with insulating tape to prevent mutual contact; disconnect negative → disconnect DC bus → drain coolant → remove fuse → remove CSU (shunt) → disconnect high-voltage box wiring harness connector → lift upper and lower copper bars and remove copper bar fixing bolts → disconnect inlet and outlet water pipes → remove high-voltage box 4 fixing bolts → take it off. Installation in reverse order: high-voltage box 4 bolts → connect inlet and outlet water pipes → install lower copper bar (bolts 10N·m) → install upper copper bar (bolts 10N·m) → connect wiring harness connector.

Safety Warnings

• This article is for technical reference only; traction battery maintenance must be performed by certified personnel according to OEM specifications; readers unfamiliar with the procedure are strictly prohibited from operating on their own.
• When removing the traction battery assembly, insulating gloves must be worn as specified; for high-voltage box internal operations, wear insulating protective gloves and wrap wiring harness connectors with insulating tape.
• Disconnect the battery negative cable and DC bus before disassembly; prepare a waste fluid container before draining coolant.
• After replacing the BMS, reprogramming and configuration are mandatory, and a road test of at least 10 minutes is required to confirm; when thermal runaway DTCs appear, prioritize handling according to OEM procedures, and never clear codes and return the vehicle directly.
• Battery pack fixing bolts must be tightened to 78N·m in layers; during installation, move the platform cart slowly to prevent interference.

Maintenance Insights

The Geometry C battery pack manual writes "when the battery is considered dangerous" as 14 determinable combined conditions—Vmin below 2.1V, temperature exceeding 67°C, temperature rise rate exceeding 3°C/s, temperature difference exceeding 30°C, all NTCs in a module failed—any combination triggers a thermal runaway report. The three numbers to remember most on site: insulation resistance 500Ω/V (common threshold for fast/slow charging, code set if below for 20 seconds), temperature difference 25°C for 60 seconds (temperature difference code exposes module inconsistency earlier than cell temperature code), pre-charge 600ms (pre-charge timeout or short circuit reported twice within 70ms points to the pre-charge circuit rather than the battery itself). Additionally, the Geometry C integrates the BMS inside the pack, and the B-BOX is separately replaceable—replacing the BMS requires going through the "fuse" and "coolant" two procedures, and the copper bar bolts in the high-voltage box are only 10N·m; these procedural details are more easily overlooked than the DTCs themselves.

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【This article is for reference only】