🔧 Highlander - Ignition Coil Replacement

Replacing the ignition coils on your Highlander means removing the coil-on-plug units that sit directly on top of the spark plugs. A bad ignition coil can cause misfires, rough idle, poor acceleration, flashing check engine light, or codes like P0301-P0306.

Difficulty Level: Beginner to Intermediate | Estimated Time: 0.5-1.5 hours for front bank, 2.5-4 hours if replacing all six

---

⚠️ Safety & Precautions

• ⚠️ Let the engine cool completely before starting. The ignition coils sit on the cylinder heads and can be very hot.
• ⚠️ Disconnect the negative battery cable before unplugging ignition coils to reduce electrical risk.
• ⚠️ Do not pull on wiring. Always release the connector lock and pull the connector body.
• ⚠️ If replacing rear-bank coils, the upper intake plenum must be removed. Cover open intake ports so nothing falls into the engine.
• ⚠️ If the check engine light was flashing, avoid driving until the misfire is fixed because raw fuel can damage the catalytic converters.

---

🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 3/8-inch ratchet
• 3/8-inch extension set
• Torque wrench rated 5-80 ft-lbs
• Flat-blade screwdriver
• Trim clip removal tool
• Needle-nose pliers
• OBD2 scan tool
• Shop vacuum
• Clean shop towels
• Nitrile gloves
• Safety glasses

---

🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Ignition coil - Qty: 1-6
• Upper intake plenum gasket set - Qty: 1 if replacing rear-bank coils
• Throttle body gasket - Qty: 1 if throttle body is removed
• Dielectric grease - Qty: 1 small tube

---

📋 Before You Begin

• 🚗 Park your Highlander on level ground, shift to Park, and set the parking brake.
• 🔋 Use a 10mm socket to disconnect the negative battery cable. Move the cable aside so it cannot touch the battery post.
• 🧠 Use an OBD2 scan tool to read misfire codes before removing parts. Cylinder codes match coil locations: P0301 is cylinder 1, P0302 is cylinder 2, and so on.
• 📍 On the V6 engine, the front bank is easier to access. The rear bank is under the upper intake plenum.
• 🧽 Use a shop vacuum to clean loose dirt from the top of the engine before removing coils.
• 🧰 A torque wrench is a tool that tightens bolts to the correct tightness so they are not too loose or too tight.
• 🧰 Dielectric grease is non-conductive silicone grease used lightly inside the coil boot to keep moisture out.

---

🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the Engine Cover

• Use your hands to lift the plastic engine cover straight upward from its rubber mounting grommets.
• Set the cover aside where it will not get stepped on.
• Pull upward evenly.

Step 2: Clean Around the Ignition Coils

• Use a shop vacuum to remove dust, leaves, and grit from around the ignition coils.
• Use clean shop towels to wipe the area around the coil tops.
• This keeps dirt from falling into the spark plug tubes when the coils are removed.

Step 3: Disconnect the Battery

• Use a 10mm socket and 3/8-inch ratchet to loosen the negative battery terminal nut.
• Lift the negative cable off the battery post and position it away from the battery.
• Do not disconnect the positive cable for this repair.

Step 4: Unplug the Front Ignition Coil Connectors

• Use your thumb or a small flat-blade screwdriver to gently press the locking tab on each front ignition coil connector.
• Pull the connector straight back by the plastic connector body.
• If the connector is stuck, use the flat-blade screwdriver gently under the connector edge, not under the wires.
• Plastic clips get brittle with age.

Step 5: Remove the Front Ignition Coil Bolts

• Use a 10mm socket, 3/8-inch extension, and 3/8-inch ratchet to remove the ignition coil hold-down bolt.
• Keep each bolt in a small tray or safe spot.
• The hold-down bolt is the small bolt that keeps the coil seated in the spark plug tube.

Step 6: Remove the Front Ignition Coils

• Grip the ignition coil body with your hand.
• Twist it gently left and right to loosen the rubber boot.
• Pull the coil straight upward out of the spark plug tube.
• If it resists, keep twisting gently while pulling upward. Do not pry hard against the valve cover.

Step 7: Install the New Front Ignition Coils

• Apply a very small amount of dielectric grease inside the end of the new coil boot using a clean shop towel or gloved finger.
• Slide the new ignition coil straight down into the spark plug tube.
• Push until you feel the boot seat onto the spark plug.
• Use a 10mm socket and torque wrench to install the hold-down bolt. Torque to 10 Nm (89 in-lbs).
• Reconnect the electrical connector until it clicks.
• A click means it is locked.

Step 8: Access the Rear Ignition Coils If Replacing All Six

• Use a trim clip removal tool to remove any plastic clips holding intake duct covers or harness retainers in your way.
• Use a 10mm socket to loosen the air intake tube clamp at the throttle body.
• Use needle-nose pliers to release small hose clamps if fitted on vacuum or breather hoses.
• Use a flat-blade screwdriver to gently help slide hoses off their fittings if they are stuck.
• Label hoses and connectors with tape if needed so they return to the same place.

Step 9: Remove the Upper Intake Plenum for Rear Coil Access

• Use a 10mm socket and 12mm socket with a 3/8-inch ratchet and extension to remove upper intake plenum fasteners and brackets.
• Unplug any electrical connectors attached to the plenum using your fingers or a flat-blade screwdriver to release connector locks.
• Carefully lift the upper intake plenum enough to access the rear ignition coils.
• Remove the old upper intake plenum gaskets.
• Cover the open intake ports immediately with clean shop towels.
• Do not drop anything inside.

Step 10: Replace the Rear Ignition Coils

• Use a flat-blade screwdriver gently to release each rear ignition coil connector lock.
• Use a 10mm socket, 3/8-inch extension, and 3/8-inch ratchet to remove each rear ignition coil hold-down bolt.
• Twist each ignition coil gently and pull it straight upward.
• Apply a small amount of dielectric grease inside each new coil boot.
• Install each new ignition coil straight down until seated.
• Use a 10mm socket and torque wrench to tighten each coil bolt. Torque to 10 Nm (89 in-lbs).
• Reconnect each coil connector until it clicks.

Step 11: Reinstall the Upper Intake Plenum

• Remove the clean shop towels from the intake ports and verify nothing is inside.
• Install the new upper intake plenum gasket set by hand into the gasket grooves.
• Lower the upper intake plenum into place carefully.
• Use a 10mm socket, 12mm socket, extension, and torque wrench to tighten the plenum fasteners evenly in stages. Torque to 21 Nm (15 ft-lbs).
• Reconnect all vacuum hoses, breather hoses, brackets, and electrical connectors using needle-nose pliers where clamps are fitted.
• If the throttle body was removed, install a new throttle body gasket and use a 10mm socket with torque wrench. Torque to 10 Nm (89 in-lbs).

Step 12: Reinstall the Intake Tube and Engine Cover

• Use a 10mm socket to tighten the air intake tube clamp at the throttle body.
• Use the trim clip removal tool or your fingers to reinstall any plastic clips or harness retainers.
• Press the engine cover straight down onto its rubber mounting grommets by hand.

Step 13: Reconnect the Battery

• Place the negative battery cable back onto the negative battery post.
• Use a 10mm socket and 3/8-inch ratchet to tighten the terminal nut snugly.
• Do not overtighten the terminal because it can crack.

Step 14: Clear Codes and Start the Engine

• Use an OBD2 scan tool to clear stored misfire codes.
• Start the engine and let it idle.
• Listen for smooth idle and check that the check engine light does not flash.
• If the engine idles very high at first, let it stabilize for a few minutes after the battery reconnect.

---

✅ After Repair

• ✅ Let the engine idle for 3-5 minutes and listen for rough running.
• ✅ If the upper intake plenum was removed, listen for a hissing sound that could indicate a vacuum leak.
• ✅ Take a short test drive with light acceleration first, then moderate acceleration.
• ✅ Recheck for codes with an OBD2 scan tool after the test drive.
• ✅ If the same cylinder misfire returns, the spark plug, fuel injector, wiring, or compression may need diagnosis.

---

💰 DIY vs Shop Cost

Shop Cost: $250-$950 depending on one coil versus all six and whether rear-bank access is needed

DIY Cost: $45-$420 depending on coil quantity and gasket needs

You Save: $150-$530 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 0.5-3.0 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.