🔧 Sonata - Spark Plug Replacement

On your Sonata, the spark plugs ignite the air/fuel mix in the gas engine. Replacing them at the correct interval helps prevent misfires, rough idle, and poor fuel economy.

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

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⚠️ Safety & Precautions

• ⚠️ Make sure the car is fully OFF (not in READY) before starting.
• ⚠️ Keep the smart key/fob at least 10+ feet away so the system can’t wake up.
• ⚠️ Disconnect the 12V battery negative terminal to prevent the engine from auto-starting during service.
• ⚠️ Work on a cold engine only; hot aluminum threads can strip easily.
• ⚠️ Do not pull on wiring—always release connector locks first.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 1/4" drive ratchet
• 3/8" drive ratchet
• 3/8" torque wrench (10-40 Nm range)
• 6" extension (3/8" drive)
• 12" extension (3/8" drive)
• 16mm spark plug socket (5/8", rubber insert)
• Small flat trim tool
• Compressed air blow gun
• Flashlight

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs - Qty: 4
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground and make sure the vehicle is OFF (not READY).
• Let the engine cool completely (at least 1 hour after driving).
• Open the trunk and disconnect the 12V battery negative terminal using a 10mm socket, then wait 5 minutes.
• Take a photo of coil connector routing.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Lift the plastic engine cover straight up to release the rubber grommets (use a small flat trim tool if it’s stuck).
• Set the cover aside.

Step 2: Unplug and unbolt the ignition coils

• On each coil, press the connector lock and unplug it (use a small flat trim tool gently if needed).
• Remove the coil hold-down bolt using a 10mm socket and 1/4" drive ratchet.
• Twist the coil slightly and pull it straight up to remove it.
• Do one cylinder at a time to avoid mix-ups.

Step 3: Clean the spark plug wells

• Blow out dirt/debris around each plug using a compressed air blow gun.
• This prevents grit from falling into the engine when the plug comes out.

Step 4: Remove the old spark plugs

• Install the 16mm spark plug socket (5/8", rubber insert) on a 6" extension (3/8" drive) and 3/8" drive ratchet.
• Turn counterclockwise to loosen, then spin out and lift the plug out with the socket.
• If a plug feels extremely tight, stop and work it back-and-forth gently—don’t force it on an aluminum head.

Step 5: Install the new spark plugs

• Verify you have the correct plugs (same length/seat style as removed).
• Start each new plug by hand using the 16mm spark plug socket (5/8", rubber insert) and extension only (no ratchet at first) to prevent cross-threading.
• Once finger-tight, tighten with a 3/8" torque wrench (10-40 Nm range): Torque to 24-29 Nm (18-21 ft-lbs).
• Do not adjust iridium plug gap.
• Avoid anti-seize unless plug maker requires it.

Step 6: Reinstall ignition coils

• Apply a tiny amount of dielectric grease inside each coil boot.
• Push the coil straight down until it fully seats on the spark plug.
• Install the coil hold-down bolt using a 10mm socket, then tighten with a 3/8" torque wrench (10-40 Nm range): Torque to 8-10 Nm (71-89 in-lbs).
• Reconnect each coil electrical connector until it clicks.

Step 7: Reinstall engine cover and reconnect 12V battery

• Press the engine cover back into place until all grommets seat.
• Reconnect the 12V battery negative terminal using a 10mm socket.

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✅ After Repair

• Start your Sonata and let it idle for 30-60 seconds; it should run smooth with no flashing check-engine light.
• If you notice a rough idle or a flashing light, shut it off and re-check that every coil connector is fully clicked in.
• Road test for 10 minutes and recheck for any warning lights.

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💰 DIY vs Shop Cost

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

DIY Cost: $50-$140 (parts only)

You Save: $200-$310 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.