🔧 Highlander - Spark Plug Replacement

On your Highlander’s V6, three plugs are easy to reach in the front bank, but the rear bank sits under the upper intake manifold. The job is mostly careful disassembly, keeping dirt out of the engine, and reinstalling everything without vacuum leaks.

Difficulty Level: Advanced | Estimated Time: 3-5 hours

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⚠️ Safety & Precautions

• 🛑 Work on a fully cool engine to avoid burns and damaged threads.
• 🛑 Disconnect the negative battery cable before unplugging coils/sensors.
• 🛑 Keep dirt out of the intake ports—stuff clean rags in openings immediately.
• 🛑 Do not use anti-seize on Toyota iridium plugs; it can cause over-torque.
• 🛑 Use only hand tools to start spark plugs to avoid cross-threading.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 12mm socket
• 14mm spark plug socket
• 3/8" ratchet
• 3/8" torque wrench (10-30 ft-lbs range)
• 6" extension (3/8")
• 12" extension (3/8")
• 3/8" universal joint
• Flathead screwdriver (medium)
• Needle-nose pliers
• Trim clip removal tool
• Pick tool (small)
• Shop vacuum
• Flashlight
• Fender cover

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs - Qty: 6
• Upper intake manifold gasket set - Qty: 1
• Dielectric grease - Qty: 1

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📋 Before You Begin

• 🧰 Park on level ground, shift to Park, and set the parking brake.
• 🧰 Open the hood and remove the plastic engine cover (pull up at the corners).
• 🧰 Disconnect the negative battery cable using a 10mm socket and move it aside so it can’t spring back.
• 🧰 Label any vacuum hoses or electrical connectors with tape as you unplug them. Photos help a lot.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the air intake ducting

• Loosen the hose clamps with a flathead screwdriver (medium).
• Unplug the MAF connector (on the intake tube) by pressing the tab and pulling straight off.
• Remove the intake tube/air duct and set it aside.

Step 2: Replace the front bank spark plugs (front 3 cylinders)

• Unplug each ignition coil electrical connector by pressing the lock tab.
• Remove each coil hold-down bolt using a 10mm socket.
• Twist the coil slightly and pull it straight up to remove it.
• Before removing the plug, vacuum around the spark plug wells using a shop vacuum. Keep grit out of the engine.
• Remove the spark plug using a 14mm spark plug socket, 3/8" ratchet, and a 6" extension (3/8").
• Install the new plug by hand using the 14mm spark plug socket and extension only (no ratchet at first) until fully seated.
• Tighten with a 3/8" torque wrench (10-30 ft-lbs range): Torque to 18 Nm (13 ft-lbs).
• Apply a small dab of dielectric grease inside the coil boot, reinstall the coil, and reinstall the bolt with a 10mm socket.

Step 3: Remove the upper intake manifold (to access the rear 3 plugs)

• Disconnect the electrical connectors and vacuum lines attached to the upper intake manifold using a pick tool (small) as needed to gently lift locking tabs.
• Remove any brackets that block access using a 10mm socket and 12mm socket.
• Unbolt the upper intake manifold fasteners using a 12mm socket, keeping track of bolt locations (some lengths can differ).
• Lift the upper intake manifold straight up and off.
• Immediately cover the exposed intake ports with clean rags.
• Remove the old upper intake manifold gaskets with a pick tool (small).

Step 4: Replace the rear bank spark plugs (rear 3 cylinders)

• Unplug each rear ignition coil connector and remove the coil bolts using a 10mm socket.
• Pull the coils out.
• Vacuum around each plug well using a shop vacuum.
• Remove each rear spark plug using a 14mm spark plug socket, 3/8" universal joint, 12" extension (3/8"), and a 3/8" ratchet.
• Install each new plug by hand first, then tighten with a 3/8" torque wrench (10-30 ft-lbs range): Torque to 18 Nm (13 ft-lbs).
• Add a small dab of dielectric grease inside each coil boot, reinstall coils, and snug the coil bolts with a 10mm socket.

Step 5: Reinstall the upper intake manifold

• Install the new upper intake manifold gaskets into place.
• Remove the rags from the intake ports and do a final check with a flashlight to confirm nothing fell in.
• Set the upper intake manifold back in place evenly.
• Install all manifold bolts finger-tight first, then tighten evenly using a 12mm socket.
• Reconnect all vacuum hoses and electrical connectors (use your labels/photos).

Step 6: Reassemble the air intake and reconnect the battery

• Reinstall the intake tube and tighten clamps using a flathead screwdriver (medium).
• Reconnect the MAF connector.
• Reconnect the negative battery cable using a 10mm socket.
• Reinstall the engine cover.

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✅ After Repair

• 🔍 Start the engine and let it idle. It should run smooth within a few seconds.
• 🔍 Listen for hissing (vacuum leak) around the upper intake area.
• 🔍 If you get a check engine light or rough idle, re-check every intake connector and vacuum hose you touched.
• 🔍 Test drive 5-10 minutes, then recheck for any new warnings.

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💰 DIY vs Shop Cost

Shop Cost: $450-$900 (parts + labor)

DIY Cost: $70-$180 (parts only)

You Save: $280-$830 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 3-5 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.