🔧 Highlander - Spark Plug Replacement

On your Highlander’s 3.5L V6, there are 6 spark plugs—3 in the front bank (easy access) and 3 in the rear bank (requires removing the upper intake manifold for access). Replacing them restores smooth starting, power, and fuel economy, and prevents misfires.

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

---

⚠️ Safety & Precautions

• ⚠️ Work on a fully cool engine to avoid burns and stripped threads in the cylinder heads.
• ⚠️ Disconnect the negative battery cable to prevent accidental shorting and coil damage.
• ⚠️ Keep dirt out of the engine—blow out plug wells before removing plugs.
• ⚠️ Do not change the spark plug gap on iridium plugs; they’re pre-set and can be damaged.

---

🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 10mm socket
• 12mm socket
• 3/8" ratchet
• 3/8" torque wrench (10-80 ft-lbs range)
• 1/4" torque wrench (50-150 in-lbs range)
• 6" extension (3/8")
• 12" extension (3/8")
• 3/8" universal joint
• 5/8" thin-wall spark plug socket
• Flat trim clip tool
• Needle-nose pliers
• Shop vacuum
• Compressed air blow gun
• Telescoping magnet pickup tool
• Painter’s tape
• Marker pen
• Clean shop rags

---

🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plugs (iridium) - Qty: 6
• Upper intake manifold gasket set - Qty: 1
• Throttle body gasket - Qty: 1
• Dielectric grease - Qty: 1

---

📋 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 cable and isolate it so it can’t spring back.
• 🧰 Label any hoses/connectors you remove using painter’s tape and a marker.

---

🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Use your hands to pull up and remove the engine cover (it’s held by rubber grommets).
• Set it aside where it won’t get stepped on.

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

• Locate the three ignition coils. An ignition coil is the small module on top of each spark plug.
• Unplug one coil at a time (press the connector tab, then pull) so nothing gets mixed up.
• Use a 10mm socket and 3/8" ratchet to remove the coil hold-down bolt.
• Twist the coil gently, then pull it straight up and out.
• Use compressed air blow gun to blow debris out of the spark plug well.
• Use a 5/8" thin-wall spark plug socket, 6" extension, and 3/8" ratchet to remove the spark plug.
• Install the new spark plug by hand first using the socket/extension only (no ratchet) to avoid cross-threading. Hand-threading prevents expensive damage.
• Torque the spark plug: Torque to 25 Nm (18 ft-lbs)
• Apply a small dab of dielectric grease inside the coil boot (the rubber spark plug “socket”).
• Reinstall the coil and bolt: Torque to 8 Nm (71 in-lbs)
• Reconnect the coil electrical connector.
• Repeat for the other two front bank cylinders, one at a time.

Step 3: Remove the air intake ducting to access the rear bank area

• Use a 10mm socket to loosen the intake hose clamps as needed.
• Use needle-nose pliers to release any spring clamps on small hoses (if equipped).
• Carefully disconnect any attached sensor connectors.
• Remove the intake ducting and set it aside.

Step 4: Remove the throttle body (to remove the upper intake manifold)

• Unplug the throttle body electrical connector.
• Use a 10mm socket and 3/8" ratchet to remove the throttle body bolts.
• Remove the throttle body and the old gasket.
• Cover the opening with a clean rag to prevent dropping anything into the intake.
• When reinstalling later, torque throttle body bolts: Torque to 10 Nm (89 in-lbs)

Step 5: Remove the upper intake manifold (rear bank access)

• Disconnect any vacuum/PCV hoses attached to the upper intake manifold, using needle-nose pliers as needed.
• Unplug any connectors clipped to the manifold (move harnesses aside gently).
• Use a 12mm socket, extensions, and 3/8" ratchet to remove the upper intake manifold bolts/nuts.
• Lift the upper intake manifold straight up and off.
• Immediately place clean rags in the lower intake ports to keep hardware out of the engine.
• Remove and discard the old upper intake manifold gaskets.

Step 6: Replace the rear bank spark plugs (firewall side)

• Just like the front, work one cylinder at a time: unplug one coil, remove the 10mm socket coil bolt, then pull the coil out.
• Use compressed air blow gun to blow out the plug well.
• Use a 5/8" thin-wall spark plug socket, extensions, and a 3/8" universal joint to remove the spark plug.
• Hand-thread the new spark plug first, then torque: Torque to 25 Nm (18 ft-lbs)
• Apply a small dab of dielectric grease inside the coil boot.
• Reinstall the coil bolt: Torque to 8 Nm (71 in-lbs)
• Reconnect the coil connector.
• Repeat for the remaining rear bank cylinders.

Step 7: Reinstall the upper intake manifold

• Remove the rags from the intake ports and verify nothing fell in (use a telescoping magnet pickup tool and shop vacuum if needed).
• Install the new upper intake manifold gaskets in their grooves.
• Set the upper intake manifold in place.
• Install bolts/nuts finger-tight first, then tighten evenly.
• Torque upper intake manifold fasteners: Torque to 21 Nm (15 ft-lbs)
• Reconnect all hoses and electrical connectors you removed.

Step 8: Reinstall the throttle body and intake ducting

• Install the new throttle body gasket, then reinstall the throttle body.
• Torque throttle body bolts: Torque to 10 Nm (89 in-lbs)
• Reconnect the throttle body electrical connector.
• Reinstall the intake ducting and tighten clamps using a 10mm socket.
• Double-check every hose clamp and connector is fully seated.

Step 9: Reconnect the battery and reinstall the engine cover

• Use a 10mm socket to reconnect the negative battery cable.
• Press the engine cover back onto its grommets.

---

✅ After Repair

• ✅ Start the engine and let it idle for 2-3 minutes. It may idle slightly high at first after throttle body removal.
• ✅ Listen for vacuum leaks (hissing) around the upper intake manifold and throttle body.
• ✅ If you get a check engine light or rough running, recheck coil connectors and intake hoses first.
• ✅ Do a short test drive, then recheck for any loose clamps or oil smell from spilled fluids (if any).

---

💰 DIY vs Shop Cost

Shop Cost: ₹12,000-₹25,000 (parts + labor)

DIY Cost: ₹3,500-₹9,000 (parts only)

You Save: ₹8,500-₹16,000 by doing it yourself!

Shop labor rates vary but typically run ₹800-₹1,500/hour. This repair takes a shop approximately 2.5-4.0 hours.

---

🎯 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.