🔧 Ioniq - Spark Plug Replacement

Your Ioniq’s spark plugs ignite the air/fuel mix. Worn plugs can cause rough running, misfires, poor fuel economy, and hard starts. This job is straightforward because the plugs sit on top of the engine under the ignition coils.

Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and thread damage in the aluminum cylinder head.
• ⚠️ Make sure the car is OFF and the READY light is not on; keep the key fob at least 10 feet away so the system can’t wake up.
• ⚠️ Do not touch or unplug any orange high-voltage cables or hybrid components.
• ⚠️ If you choose to disconnect the 12V battery, you may lose radio presets; it’s optional for this job if the car is kept OFF.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 3/8" drive ratchet
• 3/8" drive extension set
• 5/8" spark plug socket
• Torque wrench 3/8" drive (10-30 ft-lbs range)
• Trim clip tool
• Compressed air blow gun
• Clean shop towels

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (OEM-spec for Ioniq Hybrid) - Qty: 4
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground and let the engine cool completely.
• Confirm the car is OFF and the cluster does NOT show READY.
• Open the hood and remove any loose jewelry or lanyards.
• If you plan to disconnect the 12V battery: remove the negative terminal using a 10mm socket and isolate it so it can’t spring back.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover (if equipped)

• Pull up evenly on the engine cover to release the rubber grommets (use a trim clip tool only if needed).
• Set the cover aside where it won’t get stepped on.

Step 2: Unplug and remove the ignition coils

• Locate the ignition coils on top of the engine (one coil per spark plug).
• Press the connector lock and unplug each coil connector by hand.
• Remove each coil hold-down bolt using a 10mm socket and 3/8" ratchet.
• Twist the coil slightly, then pull it straight up to remove it.
• Keep coils in order, one per cylinder.

Step 3: Clean the spark plug wells

• Blow out dirt around each plug hole using a compressed air blow gun.
• Wipe any loose debris with clean shop towels.
• Dirt in the hole can damage the engine.

Step 4: Remove the old spark plugs

• Install a 5/8" spark plug socket on a 3/8" extension and 3/8" ratchet.
• Turn counterclockwise to loosen, then remove each plug carefully.
• Check each old plug for oil or heavy deposits; that can point to other issues.

Step 5: Install the new spark plugs

• Start each new plug by hand using the 5/8" spark plug socket and extension only (no ratchet at first) to avoid cross-threading.
• Once finger-tight, tighten using a torque wrench 3/8" drive (a torque wrench tightens to a set force so you don’t strip threads).
• Tighten spark plugs to Torque to 15-25 Nm (11-18 ft-lbs).
• Do not use anti-seize unless the plug maker specifically requires it.
• New iridium plugs are typically pre-gapped.

Step 6: Reinstall the ignition coils

• Apply a very small smear of dielectric grease inside each coil boot (optional but helpful).
• Push each coil straight down until fully seated on the plug.
• Install coil hold-down bolts using a 10mm socket and ratchet, then Torque to 7-9 Nm (62-80 in-lbs).
• Reconnect all coil electrical connectors until they click.

Step 7: Reinstall the engine cover

• Align the cover with the mounting grommets and press down evenly by hand.
• If you disconnected the 12V battery, reconnect it using a 10mm socket.

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✅ After Repair

• Start your Ioniq and verify it idles smoothly and no warning lights appear.
• Take a short test drive and confirm there’s no hesitation under light acceleration.
• If you had a check engine light for misfire before, scan and clear codes after confirming the fix.
• Recheck for any loose connectors or tools left in the engine bay.

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💰 DIY vs Shop Cost

Shop Cost: $250-$450 (parts + labor)

DIY Cost: $40-$120 (parts only)

You Save: $130-$410 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.0-1.5 hours.

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🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.