Battery Management System (BMS)

This procedure covers the diagnosis, replacement, and reprogramming of the Battery Management System (BMS) module on the 2023 Chevrolet Bolt EUV electric vehicle.

Warnings

Tools required

Parts

• Battery Management System (BMS) module × 1 — Use OEM specification
• High-voltage connector seals (if damaged) × 1 — Use OEM specification
• Thermal interface pad × 1 — Use OEM specification
• Coolant (if draining battery thermal system) × 1 — ACDelco DEX-COOL

Fluids

• ACDelco DEX-COOL (Orange) — 2 qt

Preparation

1. Park vehicle on level surface and apply parking brake
2. Ensure ignition is OFF and key fob is at least 10 feet away from vehicle
3. Open hood and locate 12-volt battery in engine compartment
4. Disconnect 12-volt negative battery cable and wait 2 minutes for module de-energization
5. Verify high-voltage training certification and ensure proper PPE is available
6. Connect diagnostic scan tool and document all DTCs present
7. Retrieve battery state of charge, cell voltages, and BMS data for baseline comparison
8. Raise vehicle on lift to access underbody high-voltage battery pack

Procedure

1. 1

   Disable High-Voltage System
   Locate the high-voltage service disconnect (located under rear seat access panel). Remove rear seat cushion by releasing clips. Remove service disconnect cover. Using insulated tools, rotate service disconnect handle counterclockwise and remove service plug. Store service plug in a secure location away from vehicle. Install high-voltage lockout tag.
   ⚠️Do not proceed until service disconnect is fully removed and secured away from vehicle.
2. 2

   Verify High-Voltage System De-Energization
   Wait minimum 5 minutes for high-voltage capacitors to discharge. Don high-voltage safety gloves. Using 1000V-rated multimeter, verify zero voltage at high-voltage bus bars inside battery pack. Measure between positive and negative terminals, positive to chassis ground, and negative to chassis ground. All readings must be below 2 volts DC.
   ⚠️If any voltage reading exceeds 2V DC, do not proceed. Investigate cause of residual voltage.
3. 3

   Remove Underbody Shield and Access Covers
   Remove underbody aerodynamic shield by removing plastic push clips and bolts. Lower shield and set aside. Remove battery pack access cover by removing perimeter screws. Carefully lower cover to expose battery pack upper surface and BMS module location (typically mounted on top of battery pack near center).
   Torque spec

   Cover Screws11 Nm (8 lb-ft)
4. 4

   Disconnect Battery Thermal Management System (If Required)
   If BMS module is integrated with coolant lines, place drain pan under battery pack coolant connections. Using appropriate wrench, carefully loosen coolant line fittings at BMS module. Allow coolant to drain into pan. Cap open coolant lines to prevent contamination. Note coolant line routing and orientation for reinstallation.
   ⚠Battery coolant may be warm. Allow system to cool if vehicle was recently operated.
   Torque spec

   Coolant Line Fittings15 Nm (11 lb-ft)
5. 5

   Disconnect BMS Electrical Connections
   Locate all electrical connectors on BMS module (typically 2-4 connectors including high-voltage sense leads and low-voltage communication harness). Wearing high-voltage gloves, carefully release connector locks and disconnect each connector. For high-voltage connector bolts, remove bolts and carefully separate connectors. Label each connector for proper reinstallation. Disconnect ground cable from BMS module housing.
   ⚠High-voltage sense leads carry critical voltage monitoring signals. Do not bend or damage connector pins.
   Torque spec

   Connector Bolts7 Nm (5 lb-ft)

   Ground Cable Bolt14 Nm (10 lb-ft)
6. 6

   Remove BMS Mounting Hardware
   Identify BMS module mounting configuration. Remove sensor bolts securing any temperature sensors to module housing. Remove mounting bolts securing BMS module to battery pack housing. If bracket bolts are present, remove these as well. Support BMS module with one hand while removing final fasteners to prevent dropping.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)

   Sensor Bolts11 Nm (8 lb-ft)

   Bracket Bolts20 Nm (15 lb-ft)
7. 7

   Remove BMS Module from Battery Pack
   Carefully lift BMS module from mounting location on battery pack. Note orientation of thermal interface pad if present. Inspect mounting surface on battery pack for debris, corrosion, or damage. Clean mounting surface with isopropyl alcohol and allow to dry. Inspect removed BMS module for physical damage, corrosion, or coolant intrusion. Document condition with photos.
8. 8

   Prepare New BMS Module for Installation
   Remove new BMS module from ESD-protective packaging. Verify part number matches vehicle application and replacement requirement. If thermal interface pad is required, remove old pad from battery pack surface and clean thoroughly. Apply new thermal interface pad to BMS module mounting surface, ensuring proper alignment and no air gaps. Do not touch pad surface with bare hands.
   ℹ️Thermal interface pad ensures proper heat transfer from BMS electronics to battery cooling system.
9. 9

   Install New BMS Module
   Carefully position new BMS module onto battery pack mounting surface, aligning thermal pad and mounting holes. Ensure no wiring harnesses are pinched beneath module. Install mounting bolts and bracket bolts finger-tight initially. Tighten mounting bolts to specification in a cross-pattern sequence to ensure even seating. Install sensor bolts if temperature sensors were removed.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)

   Bracket Bolts20 Nm (15 lb-ft)

   Sensor Bolts11 Nm (8 lb-ft)
10. 10

    Reconnect BMS Electrical Connections
    Clean all connector terminals using wire brush or contact cleaner. Reconnect ground cable to BMS module housing and torque ground cable bolt to specification. Reconnect low-voltage communication connectors, ensuring positive locking engagement. For high-voltage connectors, carefully align pins and install connector halves. Apply dielectric grease to connector seals if specified. Install and torque high-voltage connector bolts to specification. Verify all connector locks are fully engaged.
    ⚠Improper high-voltage connector installation can cause arcing, module damage, or fire hazard.
    Torque spec

    Ground Cable Bolt14 Nm (10 lb-ft)

    Connector Bolts7 Nm (5 lb-ft)
11. 11

    Reconnect Battery Thermal Management System
    If coolant lines were disconnected, remove caps from coolant lines. Inspect O-rings and seals for damage and replace if necessary. Reconnect coolant line fittings to BMS module, ensuring proper thread engagement. Torque coolant line fittings to specification. Refill battery thermal management system with ACDelco DEX-COOL coolant to proper level using fill port (typically located near coolant reservoir or battery pack fill point).
    Torque spec

    Coolant Line Fittings15 Nm (11 lb-ft)
12. 12

    Reinstall Access Covers and Underbody Shield
    Position battery pack access cover and install cover screws, torquing to specification. Ensure cover seal is properly seated to maintain environmental protection. Reinstall underbody aerodynamic shield, aligning clips and fasteners. Verify no tools or parts are left in battery compartment or underbody area.
    Torque spec

    Cover Screws11 Nm (8 lb-ft)
13. 13

    Reconnect 12-Volt Battery and Program BMS Module
    Lower vehicle. Reconnect 12-volt negative battery cable. Connect GM MDI 2 diagnostic tool and launch appropriate programming software (GDS2 or TIS2Web). Select BMS module programming procedure. Enter vehicle VIN and verify correct calibration files are selected. Follow on-screen prompts to program BMS module with VIN-specific software and battery configuration data. This process typically takes 15-30 minutes. Do not interrupt power during programming.
    ⚠BMS programming requires stable battery voltage. Ensure battery charger is connected if 12V battery voltage is below 12.5V.
    ⚠️Do not reinstall high-voltage service disconnect until programming is complete and verified.
14. 14

    Reinstall High-Voltage Service Disconnect
    After successful BMS programming, verify programming completion on scan tool. Remove high-voltage lockout tag. Wearing high-voltage gloves, retrieve high-voltage service disconnect plug. Install service disconnect into receptacle and rotate clockwise until fully seated and locked. Install service disconnect cover. Reinstall rear seat cushion.
    ⚠️Ensure service disconnect is fully locked before proceeding. Partial insertion can cause arcing and system damage.
15. 15

    Perform System Verification and Calibration
    With scan tool connected, clear all DTCs from BMS module. Perform BMS self-test procedure through scan tool. Verify all battery cell voltages are reading correctly and within 50mV of each other. Check battery state of charge reading is accurate. Command BMS to perform cell balancing test if available. Verify no new DTCs are present. Test drive vehicle to confirm proper operation and regenerative braking function. Monitor BMS data during test drive for anomalies.

Reassembly

1. Ensure all high-voltage connectors are properly torqued and locked
2. Verify battery thermal management system is filled to proper level and bled of air
3. Confirm all underbody shields and covers are reinstalled
4. Remove all tools and equipment from vehicle and work area

Verification

• Connect scan tool and verify no DTCs are present in BMS module
• Verify all battery cell voltages are reading and within specification (typically 3.6-4.1V per cell)
• Confirm battery state of charge displays correctly on instrument cluster
• Test vehicle in READY mode and verify no warning lights illuminate
• Perform regenerative braking test at low speed to confirm BMS is controlling battery charging
• Verify battery thermal management system maintains proper temperature during operation
• Conduct post-repair test drive of minimum 10 miles, monitoring for any warnings or performance issues
• Re-scan for DTCs after test drive and verify no new codes are present

More procedures for this vehicle