High Voltage Interlock Service

Service or replacement of the high-voltage interlock loop system that monitors the integrity of all high-voltage connections and shuts down the battery pack if a connector is opened or damaged.

Warnings

Tools required

Parts

• High-voltage interlock loop connector × 1 — Use OEM specification
• High-voltage interlock loop wire assembly × 1 — Use OEM specification
• Connector seals/boots (as needed) × 1 — Use OEM specification
• Cable ties (UV resistant) × 5 — Use OEM specification

Preparation

1. Park vehicle on level surface and apply parking brake
2. Ensure vehicle is in Park and powered completely off (not in accessory mode)
3. Verify no charging cable is connected to vehicle
4. Open hood and locate 12V battery in engine compartment
5. Put on Class 0 high-voltage insulated gloves before proceeding
6. Consult service manual diagrams to identify all high-voltage interlock loop connection points for this specific model year
7. Have emergency contact information for high-voltage incident response readily available
8. Ensure fire extinguisher rated for electrical fires (Class C) is accessible

Procedure

1. 1

   Disconnect 12-volt battery negative terminal
   Using a 10mm wrench or socket, loosen the negative (-) terminal clamp bolt on the 12V battery. Remove the cable from the battery post and secure it away from the terminal to prevent accidental reconnection. Wait at least 2 minutes for vehicle control modules to power down completely.
   ⚠Always disconnect negative terminal first to prevent short circuits.
2. 2

   Disable high-voltage system at service disconnect
   Remove the rear cargo area floor panel to access the high-voltage battery service disconnect located on top of the battery pack. Rotate the service disconnect lever counterclockwise to the OFF position (typically 1/4 turn). The lever should lock in the OFF position. Remove the service disconnect plug completely and retain in a secure location away from the vehicle.
   ⚠️Service disconnect MUST be removed and kept with the technician at all times to prevent unauthorized re-energization.
3. 3

   Wait for capacitor discharge period
   Wait a minimum of 5 minutes with the service disconnect removed to allow high-voltage system capacitors to fully discharge. During this time, prepare tools and review the interlock loop routing diagram for this vehicle. Do not touch any orange high-voltage cables or connectors during this waiting period.
   ⚠️Capacitors can retain lethal voltage. Never skip or shorten this mandatory waiting period.
4. 4

   Verify zero voltage at high-voltage battery terminals
   Using a CAT IV rated digital multimeter, measure voltage between the positive and negative terminals of the high-voltage battery pack. Verify reading is 0-2 volts DC. Also measure from each terminal to chassis ground. All readings must be below 2 volts DC before proceeding. Document voltage readings.
   ⚠️If voltage is above 2 volts, do not proceed. Wait an additional 5 minutes and retest. If voltage persists, the system has a fault requiring professional diagnosis.
5. 5

   Remove interior trim panels for access
   Remove the rear seat cushion and driver's side B-pillar lower trim panel using panel removal tools. Remove the driver's side rocker panel trim. These panels provide access to the interlock loop wiring that runs from the battery pack through the passenger compartment to the high-voltage junction box under the hood.
6. 6

   Document existing interlock loop routing
   Before disconnecting anything, photograph the current interlock loop wire routing, connector orientations, and cable tie locations. The interlock loop consists of a low-voltage signal wire (typically yellow or green) that runs through all high-voltage connectors in series. Note which connectors include the interlock terminals (usually identified by smaller gauge wires integrated into the high-voltage connector body).
   ℹ️Proper routing is critical for preventing chafing and maintaining interlock circuit integrity. Reference photos during reassembly.
7. 7

   Disconnect interlock loop at battery pack
   Locate the interlock loop connector on the high-voltage battery pack (typically near the service disconnect area). Press the connector release tab and carefully separate the connector halves. Inspect the connector terminals for corrosion, damage, or contamination. The interlock connector is usually a small 2-4 pin connector separate from the main high-voltage connectors.
8. 8

   Trace and disconnect interlock loop at drive unit
   Follow the interlock loop forward to the drive unit (electric motor/inverter assembly) located in the front of the vehicle. Remove any covers necessary to access the high-voltage junction area. Disconnect the interlock loop connector at the drive unit by pressing the release tab and separating. Inspect connector condition.
   ⚠Even with system de-energized, handle all orange high-voltage cables with insulated gloves.
   Torque spec

   Cover Screws11 Nm (8 lb-ft)
9. 9

   Disconnect interlock loop at onboard charger
   Locate the onboard charger module (typically mounted in the front of the vehicle near the charge port). Remove the charger access cover. Disconnect the interlock loop connector at the charger module. This connector may be integrated into the main high-voltage connector assembly or be a separate smaller connector.
   Torque spec

   Cover Screws11 Nm (8 lb-ft)
10. 10

    Remove interlock loop wire assembly
    Cut cable ties securing the interlock loop wire to the vehicle harness using cable tie cutters. Carefully remove the entire interlock loop wire assembly from the vehicle, noting routing through grommets, clips, and harness channels. Inspect all grommets for damage and replace if worn or cracked.
11. 11

    Test new interlock loop continuity
    Before installation, use a continuity tester or multimeter to verify the new interlock loop wire assembly has proper continuity end-to-end. Resistance should be less than 5 ohms for the complete loop. Check that there is no continuity between the interlock circuit and any grounding points. If the loop includes any inline connectors, verify they are properly seated.
    ⚠A faulty interlock loop will prevent vehicle from energizing the high-voltage system and may not set diagnostic codes.
12. 12

    Install new interlock loop wire assembly
    Route the new interlock loop wire assembly following the exact path documented in step 6. Ensure the wire runs through all required grommets and harness channels. Maintain proper clearance from sharp edges, heat sources, and moving components. Do not pull wire tight; allow slight slack for thermal expansion and vibration.
13. 13

    Connect interlock loop at all connection points
    Connect the interlock loop connectors at the battery pack, drive unit, and onboard charger. Ensure all connectors are fully seated with audible/tactile click. Apply light pull force to verify connectors are locked. If connectors include sealing boots or covers, ensure they are properly positioned. Apply thin coat of dielectric grease to connector seals if specified by service manual.
    ⚠Partially seated connectors will cause interlock circuit failure and prevent high-voltage system operation.
14. 14

    Secure interlock loop wire with cable ties
    Secure the interlock loop wire to the vehicle harness using new UV-resistant cable ties at all original locations. Do not overtighten cable ties; they should secure the wire without deforming insulation. Ensure wire has no sharp bends (minimum 2-inch radius) and maintains clearance from exhaust components, suspension, and steering components.
15. 15

    Perform interlock loop system test
    Using the GM MDI 2 scan tool with Techline Connect, connect to the vehicle DLC. With the service disconnect still removed and 12V battery still disconnected, attempt to command the high-voltage interlock loop test using the scan tool diagnostic functions. The scan tool should report interlock loop continuity present. Resistance value should be within manufacturer specification (typically 0.5-5 ohms).
    ℹ️If scan tool reports interlock loop fault, recheck all connector seating before proceeding.
16. 16

    Reconnect 12-volt battery
    Reconnect the negative cable to the 12V battery negative terminal. Tighten the terminal clamp bolt securely using a 10mm wrench. Do not reinstall the high-voltage service disconnect yet.
17. 17

    Perform scan tool verification with 12V power
    With 12V power restored but high-voltage service disconnect still removed, use the scan tool to check for any high-voltage interlock loop fault codes. Clear any old codes that may have been set during service. Verify the scan tool shows interlock loop circuit continuity is present and resistance is within specification.
    ⚠Do not reinstall service disconnect if any interlock loop faults are present.
18. 18

    Reinstall high-voltage service disconnect
    Install the high-voltage service disconnect plug back into its receptacle on the battery pack. Rotate the lever clockwise to the ON position until it locks. Verify the lever is fully seated and locked. The high-voltage system is now energized.
    ⚠️High-voltage system is now live. Orange cables and connectors are energized up to 400 volts DC.
19. 19

    Final system verification
    Using the scan tool, verify the high-voltage system shows READY status. Check for any diagnostic trouble codes. Perform a high-voltage interlock loop test using scan tool functions. Monitor battery pack voltage on scan tool; it should show nominal pack voltage (approximately 350-400 volts depending on state of charge). Verify all high-voltage system parameters are normal.

Reassembly

1. Reinstall all interior trim panels including rocker panel trim, B-pillar trim, and rear seat cushion
2. Reinstall any high-voltage component covers removed during service, torquing cover screws to specification
3. Reinstall rear cargo floor panel over battery pack area
4. Verify all panels and covers are properly secured with no gaps or misalignment

Verification

• Power on the vehicle and verify READY indicator illuminates normally on instrument cluster
• Use scan tool to verify no high-voltage interlock loop fault codes are present
• Verify high-voltage battery pack voltage displays normally on instrument cluster or infotainment screen (typically 350-400V depending on charge level)
• Perform a test drive to verify normal propulsion system operation with no warning lights
• Verify regenerative braking functions normally during deceleration
• After test drive, use scan tool to verify no new fault codes have been set
• Verify charging system operates normally by connecting charge cable and confirming charge begins
• Document interlock loop resistance value from scan tool for service records (should be 0.5-5 ohms typically)
• Verify all trim panels are secure and properly aligned with no rattles or gaps

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