🔧 Highlander - Spark Plug Replacement

On your Highlander’s V6, there are 6 spark plugs (3 in the front bank and 3 in the rear bank). The front three are straightforward; the rear three usually require removing the upper intake manifold to access the ignition coils and plugs.

Difficulty Level: Intermediate | Estimated Time: 2.5-4.5 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and damaged threads.
• ⚠️ Disconnect the negative battery terminal to prevent accidental shorting.
• ⚠️ Keep dirt out of the intake ports—stuff clean rags in ports any time the intake is open.
• ⚠️ Do not over-tighten spark plugs; aluminum heads strip easily.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 14mm socket
• 3/8" ratchet
• 3/8" torque wrench (10-80 Nm range)
• Extension set (3", 6", 10")
• Universal joint adapter
• 14mm thin-wall spark plug socket (magnetic or rubber insert)
• Flat trim removal tool
• Needle-nose pliers
• Pick tool
• Shop vacuum
• Clean shop rags
• Flashlight
• Fender cover
• Nitrile gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs (correct fit for your Highlander V6) - Qty: 6
• Upper intake manifold gasket set - Qty: 1
• Throttle body gasket - 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 let the engine cool completely.
• Use a 10mm socket to disconnect the negative battery terminal and tuck it aside.
• Take photos before unplugging anything.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Pull up on the plastic engine cover to release it from its rubber grommets (no tools).

Step 2: Replace the front bank spark plugs (easy access side)

• Unplug an ignition coil electrical connector by pressing the tab and pulling straight back. Use a pick tool gently if the tab is stubborn.
• Remove the ignition coil hold-down bolt with a 10mm socket.
• Twist the coil slightly and pull it straight out.
• Use a shop vacuum to clean dirt from around the spark plug tube.
• Remove the spark plug using a 14mm thin-wall spark plug socket, extension, and 3/8" ratchet.
• Install the new spark plug by hand first using the spark plug socket and extension (no ratchet) to avoid cross-threading.
• Tighten with a torque wrench: Torque to 18 Nm (13 ft-lbs).
• Apply a thin smear of dielectric grease inside the coil boot (the rubber end that seals on the plug).
• Reinstall the coil and bolt using a 10mm socket, then Torque to 10 Nm (89 in-lbs).
• Reconnect the coil connector until it clicks.
• Repeat for the other two front-bank cylinders.

Step 3: Remove the cowl trim for access (rear bank)

• Remove the plastic cowl top trim clips using a flat trim removal tool.
• Remove the wiper arm nuts with a 14mm socket, then wiggle the wiper arms off their splines.
• Remove cowl panel fasteners/bolts with a 10mm socket.
• Remove any cowl brace bolts with a 12mm socket and set the brace aside.
• Lay parts out in order as you remove them.

Step 4: Remove the intake ducting

• Loosen hose clamps with a 10mm socket.
• Disconnect any small breather hoses using needle-nose pliers for the clamps.
• Lift the intake duct/air tube out.

Step 5: Remove the throttle body (to clear the upper intake)

• Unplug the throttle body connector (press tab, pull straight off).
• Remove throttle body mounting bolts using a 10mm socket.
• Pull the throttle body away and remove the old gasket.
• Set the throttle body aside carefully (do not strain wiring).
• On reassembly, install the new gasket and Torque throttle body bolts to 8 Nm (71 in-lbs) using a torque wrench.

Step 6: Remove the upper intake manifold (rear bank access)

• Label and disconnect vacuum/EVAP hoses and electrical connectors as needed (use pick tool gently on locking tabs).
• Remove the upper intake manifold bolts/nuts with a 12mm socket.
• Lift the upper intake manifold off.
• Immediately place clean shop rags into the exposed intake ports to prevent anything from falling in.
• Remove old intake gaskets and install the new gasket set during reassembly.
• On reassembly, tighten with a torque wrench: Torque upper intake manifold bolts/nuts to 21 Nm (15 ft-lbs).

Step 7: Replace the rear bank spark plugs

• Unplug each rear ignition coil connector.
• Remove each coil hold-down bolt with a 10mm socket and pull the coil out.
• Vacuum around each plug tube with a shop vacuum.
• Remove spark plugs using a 14mm thin-wall spark plug socket, extension, universal joint adapter, and 3/8" ratchet as needed for angle.
• Thread new plugs in by hand first, then tighten with a torque wrench: Torque to 18 Nm (13 ft-lbs).
• Reinstall coils and Torque coil bolts to 10 Nm (89 in-lbs).
• Reconnect coil connectors until they click.

Step 8: Reassemble intake and cowl

• Remove the rags from intake ports before installing the upper intake manifold.
• Reinstall the upper intake manifold with new gaskets. Tighten with a torque wrench: Torque to 21 Nm (15 ft-lbs).
• Reinstall the throttle body with a new gasket. Tighten with a torque wrench: Torque to 8 Nm (71 in-lbs).
• Reinstall intake ducting and tighten clamps using a 10mm socket.
• Reinstall cowl brace and panels using 12mm socket and 10mm socket.
• Reinstall wiper arms and nuts using a 14mm socket.
• Reconnect the negative battery terminal using a 10mm socket.

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✅ After Repair

• Start your Highlander and let it idle for 2-3 minutes.
• Expect a slightly rough idle for a few seconds if the throttle body was unplugged; it should stabilize.
• Check for warning lights and listen for vacuum leaks (a loud hiss can mean a hose is off).
• Do a short test drive, then re-check that there are no fuel/vacuum smells and no loose parts.

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💰 DIY vs Shop Cost

Shop Cost: $450-$850 (parts + labor)

DIY Cost: $80-$220 (parts only)

You Save: $370-$630 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2.5-4.0 hours.

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🎯 Ready to get started?

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