Mechanic Wiki: How to Bleed Coolant on a Hyundai Kona EV

Learn how to properly bleed the coolant system on a Hyundai Kona EV. Step-by-step instructions, tools needed, and troubleshooting tips for both battery and power electronics loops.

Published: June 27, 2026

Quick Answer: How to Bleed Coolant on a Hyundai Kona EV

Bleeding the coolant on a Hyundai Kona EV requires activating the electric water pump via a scan tool (GDS or compatible) and opening the manual bleed valve at the highest point of the cooling loop. Unlike gasoline cars, the Kona EV has two sealed loops — one for the high-voltage battery and one for the power electronics and motor. The process ensures trapped air is purged, preventing overheating and performance loss. For 2021+ models, a scan tool is mandatory; older models may respond to a heater-on method.

Why Bleeding the Coolant System Is Crucial for the Kona EV

Understanding the Dual Coolant Loop System

The Hyundai Kona EV doesn’t rely on a single radiator like a conventional car. Instead, it uses two independent cooling loops:

High-voltage battery loop: Cools the battery pack, inverter, and onboard charger. This loop keeps the lithium-ion cells within their safe operating temperature range.
Power electronics/motor loop: Cools the drive motor, reduction gear, and the electric heater. This loop prevents the motor from overheating during sustained high-load driving.

Air pockets in either loop can cause serious issues. I’ve seen cases where a small air lock in the battery loop triggered a “Check Cooling System” warning and forced the car into reduced power mode. In extreme cases, trapped air can lead to localized hot spots inside the battery pack, increasing the risk of thermal runaway. That’s why a proper bleed is non-negotiable after any service that opens the coolant system.

When to Bleed the Coolant

You should perform a coolant bleed on your Kona EV after:

Draining and refilling either coolant loop.
Replacing the water pump, heater, radiator, or any coolant hose.
Noticing dashboard warnings such as “Coolant Low” or “Check Cooling System.”
Diagnosing poor heater performance or inconsistent battery temperature readings.

Even if you haven’t worked on the cooling system, a slow leak can introduce air. Checking coolant level and bleeding when needed should be part of your annual maintenance routine.

Tools and Safety Preparations

Required Tools

Before you start, gather these items:

Tool	Purpose
Hyundai GDS or compatible scan tool (e.g., Launch X431 with EV software)	Activate electric water pump service mode
Approved EV coolant (Hyundai spec W90 or equivalent pink/blue low-conductivity coolant)	Refill system
Funnel with a long, narrow neck	Reach deep reservoir necks
Catch pan	Collect spilled coolant
Clean rags and latex gloves	Protect surfaces and skin
Jack and jack stands (optional)	Access underbody coolant lines if needed

Note: Do not attempt this with a generic OBD-II code reader. It won’t have the bidirectional controls needed to run the pump.

Safety Warnings

Work on a cold vehicle only. Coolant can exceed 200°F under pressure. Opening a hot system can cause severe burns.
Disconnect the 12V battery negative terminal before opening any high-voltage coolant lines. The Kona EV’s cooling loops carry low-voltage current, but safety first.
Use only the correct coolant type. Mixing coolants can cause chemical gelling, which ruins seals and clogs passages. Hyundai specifies an ethylene-glycol mix with low conductivity — typically pink or blue. Check your owner’s manual or reservoir cap.
Never bypass the high-voltage safety interlocks. The battery loop contains high-voltage connections near coolant lines. If you’re not trained to work on EV high-voltage systems, leave the battery loop to a dealer.

Step-by-Step Coolant Bleed Procedure

I’ll describe the procedure for the power electronics/motor loop first, as it’s more accessible. The battery loop follows the same logic but often requires underbody access.

Step 1: Access the Bleed Valve and Coolant Reservoir

Locate the correct coolant reservoir. The battery loop reservoir is near the front of the engine bay, typically on the left side. The power electronics loop reservoir sits closer to the passenger side, near the windshield washer tank.
Find the manual bleed valve. It’s a small brass or plastic screw positioned at the highest point of the cooling circuit. On most Kona EVs, you’ll find it on the cooler pipe above the inverter or near the heater assembly.

Step 2: Initiate the Electric Water Pump Service Mode

Connect your scan tool to the OBD-II port under the dashboard.
Power the ignition to ON (press the start button without pressing the brake pedal — do not engage READY mode).
Navigate the scan tool: Hyundai GDS > Electric Vehicle > Cooling System > Active Air Bleed.
Select the correct loop (battery or power electronics). The pump will start running and run continuously for several minutes.
Manual alternative for 2019-2020 models only: Set the heater to max temperature (HI) and fan to low, then drive at low speed (under 20 mph) for 5 minutes. This may activate the pump. For 2021+ models, the pump requires a direct service command — the manual method won’t work.

Step 3: Open the Bleed Valve

While the pump is running, slowly open the bleed valve about a quarter to half a turn using a wrench or pliers.
You’ll first see air bubbles exiting, followed by a stream of coolant. Let it flow until the stream is steady and bubble-free (this may take 30–60 seconds).
Have a rag ready to catch drips. Do not fully remove the bleed screw — only loosen it.

Step 4: Check and Refill the Reservoir

As air leaves the system, the coolant level in the reservoir will drop. Keep an eye on it and top off to the MAX line using your funnel. Do not overfill.
Let the pump run for 2–3 minutes while you monitor the flow and level. If the stream becomes intermittent, you may have released a large air pocket — continue bleeding until it’s consistent.

Step 5: Close the Bleed Valve and Stop the Pump

Tighten the bleed valve securely. “Snug plus a quarter turn” is usually enough. Overtightening can crack plastic valves.
Exit the service mode on the scan tool (select “Stop Air Bleed” or turn ignition OFF). The pump will stop.

Step 6: Final Check

Turn the ignition to READY mode (press brake pedal + start button). Check the dashboard for any warning lights.
Take a short 5–10 minute drive, then park and let the vehicle cool for 30 minutes. Recheck the coolant level in the reservoir and top off if needed.

Repeat the entire process for the second loop if you performed work on both.

Common Troubleshooting Issues

Air Lock Persists After Bleeding

Cause: The bleed valve may not be at the true highest point, or the pump didn’t run long enough.

Solution: Repeat the bleed with the vehicle parked on a slight incline — raise the front of the car for the battery loop, or the rear for the motor loop. This encourages air to migrate toward the valve. Also extend the pump run time to 5 minutes.

Coolant Reservoir Overflowing

Cause: Filling the reservoir to MAX before bleeding creates excess pressure that pushes coolant out of the overflow when air expands.

Solution: Remove excess coolant until the level is just above MIN. Re-bleed, then top off to MAX after the system stabilizes.

No Coolant Flow from Bleed Valve

Cause: The pump isn’t activated (wrong scan tool command or vehicle in READY mode), or a clog exists.

Fix: Double-check that the ignition is ON (not READY) and that you selected the correct loop. If the pump still doesn’t run, listen for a humming sound near the front of the car. No sound may indicate a failed water pump or blown fuse. Check for kinked hoses as well.

When to Seek Professional Help

You lack a compatible scan tool. For 2021+ Kona EVs, the manual method doesn’t reliably activate the pump. Attempting to bleed without tool support can leave air trapped.
Coolant leaks persist after bleeding. Drips from hoses, the water pump, or the radiator indicate a physical leak that needs repair, not just bleeding.
The high-voltage battery loop requires bleeding. Because this loop runs near high-voltage cables and connectors, a professional with EV-specific training should handle it. Mistakes can lead to electric shock or battery damage.
The dashboard shows persistent “Check Cooling System” warnings. This may point to a sensor failure or a deeper issue that diagnosis codes can uncover.

For more detailed troubleshooting of Hyundai EV cooling system warnings, check out our guide: [link to article on Hyundai Kona EV warning lights].

Frequently Asked Questions

Can I bleed the Kona EV coolant without a scan tool?

For 2019–2020 models, yes — you can try the heater method: turn the heater to HI, set the fan low, and drive gently for 5 minutes. However, this only works if the vehicle’s software activates the pump under those conditions. For 2021+ models, a scan tool is required because the pump won’t run continuously without a service command.

How often should I check the coolant level?

Check the coolant level every 12 months or 10,000 miles, whichever comes first. The system is sealed, but slow evaporation or minor leaks can cause the level to drop over time.

What happens if I don’t bleed the system correctly?

Air pockets can cause uneven cooling, leading to overheating of the battery or motor. Reduced power, increased charging times, and in extreme cases, battery damage are all possible. Incorrect bleeding can also create false low-coolant warnings that can only be cleared by a dealer.

Is the coolant in the Kona EV the same as in gas cars?

No. Gas cars use standard coolants with different additive packages. The Kona EV requires a low-conductivity ethylene glycol coolant — typically pink or blue. Using standard green coolant can corrode the aluminum heat exchangers and clog the microchannels in the battery cooling plate, leading to expensive repairs.

Can I drive the car immediately after bleeding?

Yes, but watch the temperature gauge closely for the first 10 minutes. If the gauge climbs above normal quickly, pull over and shut off the vehicle. Air that moved during driving can settle into a different spot, causing a temporary hot spot. Let it cool and re-bleed if needed.

How much coolant does the Kona EV hold?

The total system holds approximately 5.5 liters. The battery loop holds about 3.5 liters, and the power electronics loop holds about 2.0 liters. Always buy a full gallon (3.78L) of coolant to have enough for both loops plus a bit extra for future top-offs.

About the Author: Erwin Salarda is an Automotive Service Equipment Technician based in the Philippines, specializing in computerized automotive diagnostic equipment such as OBD scanners and wheel alignment systems. Since 2012, he has been actively providing technical support, equipment installation, troubleshooting, after-sales service, and hands-on training for automotive service equipment used by workshops and automotive professionals.

He has received specialized training from international suppliers and manufacturers, including Launch X431 in Shenzhen, China, Lawrence Engineering Company in Guangzhou, China, and 3Excel Wheel Alignment Company in Shenzhen, China. Through these trainings, he developed advanced expertise in automotive diagnostics, calibration, wheel alignment systems, and computerized automotive service technologies.

Erwin Salarda provides professional after-sales support and technical training for automotive diagnostic and wheel alignment equipment, helping clients maximize the performance and proper use of their tools and systems. His experience covers equipment setup, software updates, calibration procedures, troubleshooting, and operational guidance for automotive workshops and service centers.

With more than a decade of experience in the automotive equipment industry, Erwin Salarda continues to support automotive businesses by delivering reliable technical expertise and practical training solutions.

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How to Bleed Coolant on a Hyundai Kona EV | Step-by-Step Guide