EV Thermal Management System

Service and diagnostics procedure for the EV thermal management system, including coolant circuit inspection, temperature sensor testing, and valve/pump operation verification for the battery and power electronics cooling system.

Warnings

Tools required

Parts

• EV coolant temperature sensor × 1 — Use OEM specification
• Thermal management valve assembly × 1 — Use OEM specification
• Coolant line O-ring kit × 1 — Use OEM specification
• Underbody shield fasteners × 5 — Use OEM specification

Fluids

• ACDelco DEX-COOL (Orange) — 10 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Verify thermal system has cooled for minimum 2 hours (check battery pack temperature on instrument cluster)
3. Disconnect 12V auxiliary battery negative terminal and wait 2 minutes
4. Remove HV battery service disconnect plug located under rear seat cushion (orange connector)
5. Install high voltage safety lockout tag and wait minimum 5 minutes for capacitor discharge
6. Remove front undertray and underbody shields to access thermal components
7. Place coolant drain pan under thermal system drain points
8. Connect GDS2 scan tool and document any existing DTCs related to thermal management

Procedure

1. 1

   Drain EV coolant system
   Locate the thermal system drain valve on the lower coolant reservoir. Slowly open the drain valve and allow coolant to drain completely into the drain pan. Monitor the coolant for contamination, metal particles, or incorrect color. Remove the coolant reservoir cap after draining begins to allow proper venting. Coolant capacity is approximately 10 quarts total across all thermal circuits.
2. 2

   Remove thermal management system covers
   Remove the plastic cover over the thermal management control module located in the front compartment near the drive unit. Remove cover screws in a crosshatch pattern to prevent warping. Carefully disconnect the wiring harness connector from the cover-mounted components before fully removing the cover.
   Torque spec

   Cover Screws11 Nm (8 lb-ft)
3. 3

   Disconnect coolant lines from thermal valve assembly
   Identify the three-way thermal management valve assembly. Label each coolant line connection point with tape for reassembly reference. Using a flare nut wrench, carefully loosen the coolant line fittings at the valve body. Expect residual coolant drainage (approximately 8-12 oz per line). Inspect all O-rings and sealing surfaces for damage or deterioration.
   ⚠Coolant lines are under residual pressure even after draining. Loosen fittings slowly to prevent coolant spray.
   Torque spec

   Coolant Line Fittings15 Nm (11 lb-ft)
4. 4

   Remove temperature sensors
   Locate the coolant temperature sensors in the battery inlet, battery outlet, and drive unit coolant circuits. Disconnect the electrical connectors by pressing the release tab. Remove the sensor bolts and carefully extract each sensor. Inspect sensor tips for scaling, corrosion, or physical damage. Using a multimeter, measure resistance across sensor terminals and compare to specification (typically 2000-3000 ohms at 68°F).
   Torque spec

   Sensor Bolts11 Nm (8 lb-ft)
5. 5

   Test thermal management valve operation
   With valve assembly accessible, use GDS2 scan tool to command valve actuator through full range of motion. Observe valve movement and listen for abnormal sounds. Check for smooth operation without binding. If valve fails to move or shows erratic operation, it must be replaced. Disconnect electrical connector from valve and measure actuator resistance (typically 10-15 ohms).
6. 6

   Remove thermal valve assembly
   Remove the valve mounting bolts securing the thermal management valve to its bracket. Carefully lift the valve assembly free, noting the orientation and position of any alignment pins or indexing features. Inspect the valve body for cracks, coolant staining indicating leaks, or damaged ports.
   Torque spec

   Valve Mounting10 Nm (7 lb-ft)
7. 7

   Inspect coolant pump and brackets
   Locate the electric coolant pump assembly. Check for coolant residue indicating leaks at the pump housing or shaft seal. Rotate the pump impeller by hand to check for bearing play or roughness. Remove bracket bolts to access the pump mounting area. Inspect all mounting brackets for cracks, corrosion, or loose fasteners.
   Torque spec

   Bracket Bolts20 Nm (15 lb-ft)
8. 8

   Inspect battery pack thermal interface connections
   Access the battery pack thermal plate connections at the pack inlet and outlet. Verify coolant line connections are secure and show no signs of seepage. Check the thermal interface mounting bolts for proper torque. Inspect rubber isolation mounts for deterioration. Use infrared thermometer on a cold vehicle to identify any coolant flow restrictions by checking line temperatures.
   Torque spec

   Mounting Bolts27 Nm (20 lb-ft)
9. 9

   Install new temperature sensors and valve
   Apply a thin coating of fresh DEX-COOL coolant to new sensor O-rings. Install sensors into their respective ports, ensuring proper seating. Torque sensor bolts to specification. Install the thermal valve assembly, aligning any indexing pins. Torque valve mounting bolts to specification. Reconnect all electrical connectors, ensuring positive lock engagement.
   Torque spec

   Sensor Bolts11 Nm (8 lb-ft)

   Valve Mounting10 Nm (7 lb-ft)
10. 10

    Reconnect coolant lines
    Install new O-rings on all coolant line fittings, lubricating with coolant. Reconnect coolant lines to the thermal valve assembly according to the labels applied during disassembly. Hand-tighten fittings first, then torque to specification using a flare nut wrench. Verify each connection is properly seated before applying torque.
    Torque spec

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

    Refill and bleed thermal system
    Close the coolant drain valve. Using only ACDelco DEX-COOL orange coolant, fill the coolant reservoir to the COLD fill line. With GDS2 connected, run the thermal system bleed procedure to purge air from all circuits. This will cycle the coolant pump and thermal valves through their full range. Monitor coolant level and add as needed during bleeding. Total system capacity is approximately 10 quarts.
12. 12

    Test thermal system operation
    With GDS2 scan tool, monitor coolant temperatures in all three circuits (battery, drive unit, power electronics). Command the thermal management valve through all positions and verify proper coolant flow by monitoring temperature changes. Check for DTCs related to thermal system operation. Verify coolant pump operation by monitoring pump command versus actual speed.
13. 13

    Reinstall covers and shields
    Verify all electrical connectors are properly engaged. Reinstall the thermal management system cover, torquing cover screws in a crosshatch pattern to specification. Reinstall underbody shields and front undertray. Verify all fasteners are properly seated.
    Torque spec

    Cover Screws11 Nm (8 lb-ft)

Reassembly

1. Reconnect 12V auxiliary battery negative terminal
2. Reinstall HV battery service disconnect plug and verify proper engagement
3. Remove lockout/tagout tag
4. Start vehicle and verify all thermal system warnings are cleared from instrument cluster
5. Check coolant level after thermal system reaches operating temperature and top off if necessary

Verification

• Using GDS2, verify no DTCs are present in the thermal management control module
• Monitor battery pack temperature during a 20-minute drive cycle - temperature should stabilize between 59-95°F depending on ambient conditions
• Verify coolant level remains stable at HOT fill line after thermal cycling
• Inspect all coolant connections for leaks after test drive with vehicle on lift
• Perform thermal system diagnostic test with GDS2 and verify all actuators, sensors, and pumps respond within specification
• Check coolant concentration with refractometer - should read -34°F freeze protection minimum

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