Inverter Coolant Service

This procedure drains, flushes, and refills the inverter coolant system on the 2023 Chevrolet Bolt EUV electric vehicle, ensuring proper thermal management of the high-voltage power electronics.

Warnings

Tools required

Parts

• Inverter coolant drain plug O-ring × 1 — Use OEM specification
• Coolant hose clamps (if damaged) × 2 — Use OEM specification
• High-voltage connector seals (if damaged) × 2 — Use OEM specification

Fluids

• ACDelco DEX-COOL (Orange) — 10 qt

Preparation

1. Ensure the vehicle has been off for at least 2 hours and the coolant system is completely cool to the touch
2. Park the vehicle on a level surface and engage the parking brake
3. Verify you have the correct DEX-COOL coolant (orange color) - do not substitute
4. Put on high-voltage safety gloves and have insulated tools ready
5. Disconnect the negative (-) terminal of the 12V battery located in the rear cargo area
6. Wait 2 minutes for vehicle systems to power down completely
7. Raise the vehicle and support securely on jack stands at all four corners
8. Remove the front undertray/belly pan to access the inverter cooling system components

Procedure

1. 1

   De-energize the high-voltage system
   Open the rear cargo area and locate the high-voltage service disconnect beneath the cargo floor cover. Remove the service disconnect cover by turning counterclockwise, then pull the orange high-voltage disconnect lever to the OFF position. Install the service disconnect lock to prevent accidental reconnection. Wait a minimum of 5 minutes for high-voltage capacitors to discharge.
   ⚠️Do not proceed until the full 5-minute discharge waiting period has elapsed.
2. 2

   Verify high-voltage system de-energization
   Using a digital multimeter rated for high voltage, verify that voltage across the high-voltage bus is below 3V DC. Check voltage at the inverter high-voltage terminals (orange cables) using insulated test leads. Document the voltage reading. If voltage is above 3V DC, wait an additional 5 minutes and re-test.
   ⚠️Never touch high-voltage components if voltage reads above 3V DC.
3. 3

   Remove inverter access covers
   Locate the drive unit inverter assembly in the front motor compartment on the driver's side. Remove the inverter protective covers by loosening the cover screws. Carefully set covers aside in a clean area. Inspect the high-voltage connectors for any signs of damage or corrosion.
   Torque spec

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

   Disconnect inverter electrical connections
   Disconnect the low-voltage harness connectors from the inverter assembly. Loosen the high-voltage connector bolts and carefully separate the high-voltage connectors from the inverter terminals. Support the heavy high-voltage cables to prevent strain. Cover exposed high-voltage terminals with insulating tape.
   ⚠High-voltage cables are heavy and stiff. Use care to prevent damage to connector pins.
   Torque spec

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

   Drain the inverter coolant
   Position a drain pan beneath the inverter coolant drain plug located at the lowest point of the inverter cooling circuit. Remove the drain plug and allow coolant to drain completely (approximately 2-3 quarts). Inspect the drain plug O-ring for damage and replace if necessary. Once drained, loosely reinstall the drain plug to prevent debris entry.
   ⚠Coolant may still be warm. Wear appropriate protective gloves.
6. 6

   Disconnect inverter coolant hoses
   Using hose clamp pliers, reposition the coolant hose clamps on the inlet and outlet hoses connected to the inverter assembly. Carefully twist and pull the coolant hoses to separate them from the inverter fittings. Have a drain pan ready as residual coolant will drain from the hoses. Cap or plug the open hose ends to prevent contamination.
   ℹ️Mark or photograph hose routing before removal to ensure correct reassembly.
7. 7

   Remove coolant temperature sensors
   Disconnect the electrical connectors from the coolant temperature sensors on the inverter cooling circuit. Remove the sensor mounting bolts and carefully extract the sensors from their housings. Inspect the sensor O-rings for damage. Place sensors in a clean location away from debris.
   Torque spec

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

   Flush the inverter cooling passages
   Connect a coolant flush adapter to the inverter coolant inlet port. Using fresh DEX-COOL coolant or approved flushing solution, flush the inverter cooling passages until fluid runs clear from the outlet port. Ensure no debris or contamination is present. Allow to drain completely, then remove the flush adapter.
   ℹ️Do not use compressed air to flush the system as this can damage internal cooling passages.
9. 9

   Reinstall coolant temperature sensors
   Install new O-rings on the coolant temperature sensors if originals show any wear. Insert sensors into their housings and install the sensor mounting bolts, torquing to specification. Reconnect the electrical connectors ensuring they click into place securely.
   Torque spec

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

    Install new drain plug seal and close drain
    Install a new O-ring on the inverter coolant drain plug. Clean the drain plug threads and sealing surface. Install the drain plug and torque to specification using a torque wrench.
    ⚠Do not overtorque the drain plug as this may damage the inverter housing.
    Torque spec

    Mounting Bolts27 Nm (20 lb-ft)
11. 11

    Reconnect inverter coolant hoses
    Inspect coolant hose ends for damage or deterioration. Reconnect the inlet and outlet coolant hoses to the inverter fittings, ensuring they are fully seated. Position new hose clamps (or reuse if in good condition) and tighten securely. Verify hoses are routed correctly per original configuration.
    ℹ️Ensure hoses are not kinked or contacting sharp edges that could cause future leaks.
12. 12

    Refill inverter coolant system
    Using a funnel with appropriate adapter, fill the inverter coolant system through the designated fill port with fresh ACDelco DEX-COOL coolant. Fill slowly to minimize air entrapment. Add coolant until it reaches the fill port level. Allow system to settle for 5 minutes, then top off as needed. Total system capacity is approximately 10 quarts shared between all cooling circuits.
    ⚠Only use ACDelco DEX-COOL (orange) coolant. Other coolants may damage the system.
13. 13

    Bleed the inverter cooling system
    Connect a compatible scan tool to the vehicle's OBD-II port. Navigate to the high-voltage cooling system functions and command the electric coolant pump to run at 50% speed for 2 minutes. Monitor for coolant level drop and add coolant as necessary. Increase pump speed to 100% for an additional 2 minutes. Check all connections for leaks. Repeat bleeding process until no air bubbles are visible in the coolant reservoir.
    ℹ️The 12V battery must be reconnected temporarily to perform this step, but high-voltage system should remain de-energized.
14. 14

    Reconnect inverter electrical connections
    Remove insulating tape from high-voltage terminals. Carefully align and connect the high-voltage connectors to the inverter terminals. Install high-voltage connector bolts and torque to specification in a cross-pattern. Reconnect all low-voltage harness connectors ensuring proper seating. Verify all connections are secure and properly locked.
    Torque spec

    Connector Bolts7 Nm (5 lb-ft)
15. 15

    Reinstall inverter covers and finalize
    Install the inverter protective covers and tighten cover screws to specification. Reinstall the front undertray/belly pan. Lower the vehicle from jack stands. Reconnect the negative terminal of the 12V battery. Remove the high-voltage service disconnect lock and reinstall the high-voltage service disconnect to the ON position. Reinstall the service disconnect cover.
    Torque spec

    Cover Screws11 Nm (8 lb-ft)

Reassembly

1. Ensure all high-voltage connectors are properly torqued and secured before re-energizing the system
2. Verify all coolant hose clamps are tight and hoses are properly routed without kinks
3. Double-check that all electrical connectors are fully seated and locked
4. Confirm the coolant reservoir is filled to the proper level before starting the vehicle

Verification

• Using the scan tool, verify no high-voltage system fault codes are present
• Start the vehicle and allow it to run for 5 minutes while monitoring coolant temperature and level
• Verify the electric coolant pump activates and operates smoothly without unusual noise
• Inspect all inverter coolant connections for any signs of leakage
• Using the scan tool, monitor inverter temperature under light load to confirm proper cooling function (temperature should stabilize between 40-70°C)
• Test drive the vehicle for 10-15 minutes and recheck coolant level and connections after cool-down
• Clear any stored diagnostic codes and verify no new codes set after test drive

Related trouble codes on this vehicle

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