🔧 Spark Plugs - Replacement

Your Yaris uses coil-on-plug ignition, so each spark plug sits under an ignition coil. Replacing them restores smooth idle, better starting, and proper fuel economy when the plugs are worn or fouled.

Difficulty Level: Intermediate | Estimated Time: 1-2 hours

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⚠️ Safety & Precautions

• Work on a cold engine. Hot aluminum cylinder heads can be damaged if plugs are removed warm.
• Disconnect the negative battery terminal with a 10mm wrench before unplugging coils.
• Do not drop dirt into the plug wells. Keep the area clean before removing plugs.
• Use only a spark plug socket and a torque wrench. Overtightening can strip the threads in the cylinder head.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 3/8-inch ratchet
• 3-inch extension
• 5/8-inch spark plug socket
• Torque wrench
• Feeler gauge
• Flat trim tool
• Needle-nose pliers
• 10mm wrench
• Compressed air
• Shop towel
• Safety glasses
• Mechanic gloves

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plug set - Qty: 4
• Ignition coil boots - Qty: 4

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📋 Before You Begin

• Park on level ground, set the parking brake, and let the engine cool fully.
• Open the hood and make sure the engine cover area is clean before starting.
• Disconnect the negative battery cable using a 10mm wrench.
• Label coil connectors if needed.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Use a flat trim tool to carefully lift the plastic engine cover straight up.
• Set it aside where it will not crack or collect dirt.

Step 2: Disconnect the ignition coils

• Use a flat trim tool or your fingers to release each coil connector lock.
• Unplug the connectors one at a time so they do not get mixed up.
• Do one cylinder at a time.

Step 3: Remove the ignition coils

• Use a 10mm socket and 3/8-inch ratchet to remove the coil hold-down bolts.
• Pull each ignition coil straight up and out of the plug well.
• Inspect the boots for oil, cracks, or carbon tracking.

Step 4: Clean the spark plug wells

• Use compressed air to blow dirt out of each plug well before removing the plugs.
• This keeps debris from falling into the cylinder.

Step 5: Remove the old spark plugs

• Use a 5/8-inch spark plug socket, 3-inch extension, and torque wrench to loosen and remove each spark plug.
• Turn each plug counterclockwise slowly so you can feel for cross-threading.
• Remove one plug at a time.

Step 6: Check and install the new spark plugs

• Use a feeler gauge to verify the plug gap if the plugs are not pre-gapped.
• Start each new plug by hand using the spark plug socket and extension.
• Thread them in by hand first to avoid damaging the threads.
• Torque each spark plug to 18 Nm (13 ft-lbs).

Step 7: Reinstall the ignition coils

• Use the 10mm socket and torque wrench to reinstall each coil hold-down bolt.
• Torque to 8 Nm (71 in-lbs).
• Reconnect each coil electrical connector until it clicks.

Step 8: Reinstall the engine cover and battery cable

• Press the engine cover back into place by hand.
• Reconnect the negative battery cable using the 10mm wrench.

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✅ After Repair

• Start the engine and let it idle for a few minutes.
• Listen for smooth idle and check for a check engine light.
• If the engine shakes or misfires, recheck coil connectors and plug torque.
• Test drive the car gently and confirm normal acceleration.

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💰 DIY vs Shop Cost

Shop Cost: $180-$320 (parts + labor)

DIY Cost: $40-$90 (parts only)

You Save: $140-$230 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1-2 hours.

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🎯 Ready to get started?

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