🔧 Highlander - Spark Plug Replacement

Replacing the spark plugs on your Highlander helps restore smooth idle, fuel economy, and easy starting. The 2.7L inline-4 engine has four spark plugs located under the ignition coils on top of the engine.

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

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⚠️ Safety & Precautions

• ⚠️ Work only on a cold engine. Hot aluminum cylinder heads can damage plug threads.
• ⚠️ Disconnect the negative battery cable before unplugging ignition coils.
• ⚠️ Do not drop anything into the spark plug wells. Dirt can fall into the engine.
• ⚠️ Start each new spark plug by hand first. Cross-threading means the plug is going in crooked and can damage the cylinder head.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 3/8-inch ratchet
• 3/8-inch 6-inch extension
• 5/8-inch spark plug socket
• Torque wrench 5-80 ft-lbs
• Spark plug gap gauge
• Needle-nose pliers
• Compressed air blower nozzle
• Clean shop towels
• Nitrile gloves
• Safety glasses

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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 small tube

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📋 Before You Begin

• Park your Highlander on level ground and let the engine cool completely.
• Open the hood and remove the key from the vehicle.
• Use a 10mm socket to loosen the negative battery terminal, then move the cable aside so it cannot touch the battery post.
• A spark plug socket is a deep socket with a rubber insert or magnet that holds the spark plug while you lift it out.
• A torque wrench tightens fasteners to a measured amount so the spark plugs are not too loose or too tight.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the Engine Appearance Cover

• Use both hands to lift the plastic engine cover straight upward from the rubber mounting grommets.
• Set the cover aside on a clean towel.
• Pull upward evenly.

Step 2: Locate the Ignition Coils

• Find the four ignition coils on top of the engine. Each coil sits directly over one spark plug.
• An ignition coil makes the high voltage needed to fire the spark plug.
• Use a clean shop towel to wipe loose dust from the coil area.

Step 3: Unplug the First Ignition Coil

• Use your fingers to press the release tab on the first ignition coil connector.
• If the connector is stubborn, use needle-nose pliers gently on the connector lock only.
• Pull the connector straight back. Do not pull on the wires.
• One plug at a time prevents mix-ups.

Step 4: Remove the First Ignition Coil

• Use a 10mm socket, 3/8-inch ratchet, and 6-inch extension to remove the coil hold-down bolt.
• Twist the coil slightly by hand, then pull it straight up out of the spark plug well.
• Place the coil in order on a clean shop towel.

Step 5: Clean the Spark Plug Well

• Put on safety glasses.
• Use a compressed air blower nozzle to blow dirt out of the spark plug well before removing the plug.
• If you do not have compressed air, use a clean shop towel around the top area and work carefully.

Step 6: Remove the Old Spark Plug

• Use a 5/8-inch spark plug socket, 6-inch extension, and 3/8-inch ratchet to turn the spark plug counterclockwise.
• Once loose, spin it out slowly and lift it straight up with the spark plug socket.
• If the plug feels stuck, stop and tighten it slightly, then loosen again slowly.
• Never force a stuck plug.

Step 7: Check the New Spark Plug

• Use a spark plug gap gauge to verify the new plug gap is about 0.044 in.
• Most iridium spark plugs come pre-gapped. Do not pry hard on the fine center electrode.
• Do not apply anti-seize to the spark plug threads unless the plug maker specifically requires it.

Step 8: Install the New Spark Plug by Hand

• Place the new spark plug into the 5/8-inch spark plug socket.
• Use only the 6-inch extension by hand to lower the plug into the well.
• Turn clockwise by hand at least 4 full turns before using the ratchet.
• If it does not turn easily, remove it and start again.

Step 9: Torque the New Spark Plug

• Attach the torque wrench to the 5/8-inch spark plug socket and 6-inch extension.
• Tighten the spark plug to Torque to 20 Nm (15 ft-lbs).
• Do not overtighten. The cylinder head is aluminum.

Step 10: Reinstall the Ignition Coil

• Apply a small dab of dielectric grease inside the rubber boot at the bottom of the coil.
• Dielectric grease helps seal moisture out of the coil boot.
• Push the coil straight down until it seats fully over the spark plug.
• Use a 10mm socket and torque wrench to install the coil bolt to Torque to 8 Nm (71 in-lbs).

Step 11: Reconnect the Ignition Coil Connector

• Push the electrical connector onto the coil until it clicks.
• Gently tug the connector by hand to confirm it is locked.

Step 12: Repeat for the Other Three Spark Plugs

• Use the same 10mm socket, 5/8-inch spark plug socket, 6-inch extension, ratchet, and torque wrench for the remaining three cylinders.
• Replace one spark plug at a time.
• Torque each spark plug to Torque to 20 Nm (15 ft-lbs).
• Torque each ignition coil bolt to Torque to 8 Nm (71 in-lbs).

Step 13: Reinstall the Engine Cover and Battery Cable

• Align the plastic engine cover with its mounting grommets and press it down by hand until seated.
• Use a 10mm socket to reconnect and tighten the negative battery terminal.
• Make sure the terminal does not rotate by hand after tightening.

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✅ After Repair

• Start your Highlander and let it idle for 1-2 minutes.
• Listen for a smooth idle. A rough idle usually means a coil connector is loose or a coil is not fully seated.
• Check that the check engine light stays off.
• Take a short test drive, then recheck the engine area for loose connectors or tools.
• The idle may relearn briefly after the battery was disconnected.

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💰 DIY vs Shop Cost

Shop Cost: $220-$400 (parts + labor)

DIY Cost: $45-$100 (parts only)

You Save: $175-$300 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1-1.5 hours.

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🎯 Ready to get started?

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