🔧 Highlander - Spark Plug Replacement

You’ll be replacing all six spark plugs on your Highlander’s V6. This will restore smooth running, fuel economy, and easy starting, especially as mileage climbs.

Difficulty Level: Intermediate (tight access at the back bank) | Estimated Time: 2–3 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a cool engine; hot parts can burn you and damage threads in the aluminum cylinder heads.
• ⚠️ Disconnect the negative battery terminal before unplugging ignition coils to avoid short circuits.
• ⚠️ Keep dirt out of the spark plug holes; anything that falls in can damage the engine.
• ⚠️ Never over-tighten spark plugs; the cylinder head is aluminum and can strip easily.
• ⚠️ Support the hood securely and keep tools clear of the windshield cowl and glass.

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🔧 Required Tools

You'll need the following tools for this repair:

• 3/8" drive ratchet
• 1/4" drive ratchet
• 10mm socket
• 12mm socket
• 14mm thin-wall spark plug socket (magnetic or with rubber insert)
• 3/8" drive extension 6"
• 3/8" drive extension 10–12"
• 3/8" drive universal joint (swivel adapter)
• Torque wrench 3/8" drive (5–60 Nm range)
• Flat-blade trim tool or plastic pry tool
• Needle-nose pliers
• Shop vacuum with small nozzle
• Clean rag set
• Dielectric grease (ignition-safe)
• Anti-seize compound (optional, very small amount if used)
• Fender cover or thick towel
• Mechanic’s gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs (Toyota-spec Denso type for 2GR-FKS) - Qty: 6
• Ignition coil boots - Qty: 6 (optional but recommended if original)
• Throttle body gasket - Qty: 1 (if removed for access)
• Plastic cowl panel clips - Qty: 4–6 (in case any break on removal)
• Battery terminal cleaning pads - Qty: 1 (optional)
• Shop towels - Qty: 1 pack
• Electrical contact cleaner spray - Qty: 1 (optional for dirty connectors)

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📋 Before You Begin

• Park the Highlander on a flat surface, shift to Park, and set the parking brake.
• Let the engine cool completely; at least 45–60 minutes after driving.
• Open the hood and install your fender cover or towel to protect paint.
• Use a 10mm socket to loosen the nut on the negative battery terminal and remove the cable from the post; tuck it aside so it cannot spring back.
• Lay out the new spark plugs and verify you have six, all the same part number.
• Check plug gaps lightly with a feeler gauge or gap tool; they should match Toyota spec. Do not pry iridium center electrodes.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove engine cover

• Grab the plastic engine cover at the sides near the front.
• Pull straight up firmly to pop the cover off its rubber mounts.
• Lift the cover out and set it aside somewhere safe.

Step 2: Understand the layout (front vs rear bank)

• The V6 has three cylinders at the front (easy access) and three at the rear near the windshield (tighter access).
• Each cylinder has one ignition coil on top; a coil is a black plastic part with an electrical connector and a long boot going down to the plug.
• We’ll do the easier front bank first so you get practice.

Step 3: Remove intake duct (for space)

• Use a 10mm socket to loosen the clamp at the throttle body side of the air intake tube.
• Loosen the clamp at the air filter box with the same 10mm socket.
• Unclip or gently pull off any small hoses or resonators attached to the tube (remember where they go).
• Lift the intake tube off and set it aside. This gives you more room to reach the front coils.

Step 4: Unplug and remove front ignition coils (Bank 1)

• Working on one coil at a time prevents mix-ups.
• Press the small plastic tab on the coil’s electrical connector with your thumb and pull the connector straight off. Use needle-nose pliers gently if the tab is stiff.
• Use a 10mm socket and 1/4" ratchet to remove the single bolt holding the coil down. Keep the bolt in a safe spot.
• Grip the coil and twist it slightly to break the seal, then pull it straight up to remove it.
• Inspect the rubber boot for cracks, oil, or carbon tracking (black lines). Replace the boot if damaged.

Step 5: Clean around the spark plug wells

• Use your shop vacuum with a small nozzle to vacuum around the plug hole.
• This removes sand and dust so it doesn’t fall into the cylinder when the plug comes out.
• Take your time here; cleanliness really matters.

Step 6: Remove the front spark plugs

• Attach the 14mm spark plug socket to your 6" extension and 3/8" ratchet.
• Lower the socket straight down into the plug well until it seats on the plug.
• Turn counterclockwise to loosen. It may be snug at first, then should turn smoothly.
• Once loose, spin it out by hand using the extension only, then pull the plug up with the socket.
• Set the old plug aside in order so you can compare all six later.

Step 7: Prepare and install new front spark plugs

• If you choose to use anti-seize compound, apply a tiny smear to the threads only. Too much can affect torque readings.
• Install the new plug in the 14mm spark plug socket so it’s held by the rubber or magnet.
• Lower it carefully into the well and begin threading it by hand only, using the extension without the ratchet.
• Turn it clockwise gently. It should spin in easily. If you feel resistance quickly, back out and start again to avoid cross-threading.
• Once hand-tight, attach the ratchet and torque wrench to the extension.
• Use the torque wrench to tighten to 18 Nm (13 ft-lbs).
• Always use a torque wrench on spark plugs.

Step 8: Reinstall front ignition coils

• Put a small dab of dielectric grease inside the tip of the coil boot (where it meets the plug). This helps sealing and future removal.
• Lower the coil straight down onto the plug until fully seated.
• Install the 10mm bolt by hand, then tighten with a 10mm socket and 1/4" ratchet.
• If you have an inch-pound torque wrench, tighten coil bolts to about 9 Nm (80 in-lbs). Otherwise, snug plus a small extra turn is enough.
• Reconnect the coil electrical connector; it should click into place.
• Repeat Steps 4–8 for the other two front cylinders.

Step 9: Gain access to rear bank (near firewall)

• The rear three plugs sit closer to the windshield under some wiring and possibly the wiper cowl area.
• On this engine, you can reach them without removing the intake manifold, but space is tight.
• Remove any small plastic covers at the back of the engine with your flat-blade trim tool by gently prying up clips.
• You may need to unclip a wiring harness or hose bracket (usually held by plastic clips or a 10mm bolt) and move it slightly aside for room. Use a 10mm socket where needed.
• Take pictures with your phone so you remember clip positions.

Step 10: Remove rear ignition coils

• Again, do one cylinder at a time.
• Unplug the coil connectors by pressing the tab and pulling straight back. Use needle-nose pliers gently if needed.
• Use a 10mm socket and 1/4" ratchet to remove the coil bolts.
• Wiggle and pull the coils out. Space is tight, so you may need to angle them slightly.

Step 11: Remove rear spark plugs

• Use the 14mm spark plug socket with a 10–12" extension and a universal joint if needed to reach each plug straight on.
• Vacuum around each plug hole first with the shop vacuum.
• Break the plug loose with the ratchet, then remove it by hand as you did on the front bank.
• Pull the plug out and inspect for any oil or coolant traces. If you see fluids, that’s a separate issue to address later.

Step 12: Install new rear spark plugs

• Prepare each new plug the same way as the front: optional tiny smear of anti-seize on threads only.
• Place the plug in the 14mm spark plug socket, attach to the long extension (and universal joint if needed).
• Carefully lower it into the plug well, keeping everything as straight as possible.
• Thread by hand only at first. You should feel it turn smoothly several turns with no binding.
• Use the torque wrench to tighten each rear plug to 18 Nm (13 ft-lbs).

Step 13: Reinstall rear ignition coils and clips

• Add a small dab of dielectric grease inside each coil boot tip.
• Seat each coil fully on its plug.
• Install the 10mm hold-down bolts and snug them with the 10mm socket (about 9 Nm (80 in-lbs) if you can measure).
• Reconnect each coil connector until it clicks.
• Reattach any wiring harness clips, brackets, or small covers you removed earlier using the 10mm socket and trim tool.

Step 14: Reinstall intake duct and engine cover

• Reinstall the intake tube between the air filter box and throttle body.
• Slip the tube fully onto both ends, then tighten both clamps with the 10mm socket. They should be snug but not crushing.
• Reconnect any small hoses or resonators you removed earlier.
• Position the engine cover over its mounting points and press down firmly to snap it back into place.

Step 15: Reconnect the battery and initial start

• Reattach the negative battery cable to the terminal and tighten the nut with a 10mm socket so it’s snug and secure.
• Turn the ignition to ON (without starting) for a few seconds, then to OFF, then start the engine.
• The engine may idle slightly rough for a short time while the computer relearns, but it should quickly smooth out.
• If it misfires badly, shut off and recheck all coil connectors.

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✅ After Repair

• Let the engine idle for a few minutes; listen for smooth, even running and check the dash for any warning lights.
• Blip the throttle gently a few times to ensure there’s no hesitation.
• Take a short, gentle test drive, paying attention to acceleration and idle at stops.
• If the Check Engine Light comes on, have the codes read; often a loose coil connector or plug wire is the cause after this job.
• Over the next few drives, you should notice smoother running and possibly better fuel economy.

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💰 DIY vs Shop Cost

Shop Cost: $350–$550 (parts + labor)

DIY Cost: $80–$140 (parts only, depending on plug brand)

You Save: $210–$470 by doing it yourself!

Shop labor rates vary but typically run $100–$150/hour. This repair takes a shop approximately 1.5–2.0 hours.

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