🔧 Highlander - Ignition Coil Replacement

Ignition coils create the high voltage your spark plugs need. When a coil fails, your Highlander can misfire, shake at idle, lose power, and set a check-engine light. On the V6, the front-bank coils are easy to reach, while the rear-bank coils usually require removing the upper intake (plenum) for access.

Difficulty Level: Intermediate | Estimated Time: 1.5-3.0 hours

Assumption: V6 rear-bank coils require upper intake plenum removal.

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⚠️ Safety & Precautions

• ⚠️ Work on a cool engine to avoid burns.
• ⚠️ Disconnect the negative battery cable to prevent electrical shorts.
• ⚠️ Keep dirt out of the intake—cover openings with a clean rag.
• ⚠️ Do not pull on wires; release connector locks first.
• ⚠️ If you smell strong fuel vapors, stop and ventilate the area.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 1/4" drive ratchet
• 3/8" drive ratchet
• 3" socket extension
• 6" socket extension
• Universal joint adapter for sockets
• Torque wrench (inch-pound)
• Torque wrench (foot-pound)
• Flathead screwdriver
• Needle-nose pliers
• Trim clip removal tool
• Pick tool
• Shop flashlight
• Clean shop rags
• Masking tape
• Marker
• Nitrile gloves
• Safety glasses

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Ignition coil - Qty: 1-6
• Upper intake plenum gasket set - Qty: 1
• Throttle body gasket - Qty: 1
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground and set the parking brake.
• Open the hood and let the engine cool fully.
• Use 10mm socket to disconnect the negative battery terminal and move it aside.
• Use masking tape and a marker to label any hoses/connectors you unplug (simple and avoids mix-ups).
• Know the terms: the upper intake (plenum) is the top aluminum/plastic air passage feeding the engine; it must come off to reach the rear-bank coils.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Lift off the plastic engine cover (it typically pulls upward from rubber grommets). Use a shop flashlight to check for hidden fasteners before pulling hard.

Step 2: Replace front-bank coils (easy-access bank)

• Locate the three coils at the front of the engine (closest to the radiator).
• At each coil, press the connector lock and unplug it. Use a pick tool gently if the lock is stubborn.
• Remove the coil hold-down bolt using a 10mm socket.
• Twist the coil slightly, then pull it straight up to remove it.
• Put a pea-size dab of dielectric grease inside the new coil boot (the rubber end). This helps prevent moisture and makes future removal easier.
• Install the new coil straight down until it fully seats.
• Install the hold-down bolt using a 10mm socket, then Torque to 9 Nm (80 in-lbs) using an inch-pound torque wrench.
• Reconnect the electrical connector until it clicks.

Step 3: Remove the air intake tube (to access the upper intake area)

• Loosen the hose clamps using a flathead screwdriver.
• Unplug any small sensor/vent connections on the tube by hand or with needle-nose pliers for clamps.
• Remove the intake tube and set it aside with a clean shop rag covering the throttle opening area if needed.

Step 4: Disconnect hoses and connectors from the upper intake (label everything)

• Use masking tape and a marker to label vacuum hoses and electrical connectors you remove.
• Release spring clamps using needle-nose pliers, then slide clamps back on the hose and pull the hose off by twisting gently.

Step 5: Remove the throttle body (move it aside)

• Unplug the throttle body connector by pressing the lock and pulling straight off.
• Remove the throttle body mounting fasteners using a 10mm socket.
• Carefully separate the throttle body and remove the old gasket.
• Set the throttle body aside in a clean area (do not drop it).

Step 6: Remove the upper intake (plenum)

• Remove the upper intake bolts/nuts using a 12mm socket with a 6" socket extension and universal joint adapter for sockets where needed.
• Lift the plenum up and off carefully, checking that no hoses/wires are still attached.
• Immediately place clean shop rags in the exposed intake ports so nothing falls in.

Step 7: Replace rear-bank coils (rear bank under the plenum)

• Locate the three coils at the rear of the engine (closest to the firewall).
• Unplug each coil connector (use a pick tool gently on the lock if needed).
• Remove each coil hold-down bolt using a 10mm socket.
• Remove each coil by twisting slightly and pulling straight up.
• Add a small amount of dielectric grease inside each new coil boot.
• Install each new coil and bolt it down with a 10mm socket.
• Torque to 9 Nm (80 in-lbs) using an inch-pound torque wrench.
• Reconnect the connectors until they click.

Step 8: Reinstall the upper intake with new gaskets

• Remove the old upper intake gaskets and install the new ones from the upper intake plenum gasket set.
• Remove the clean shop rags from the intake ports (double-check you removed all of them).
• Set the plenum back in place carefully.
• Install bolts/nuts by hand first to avoid cross-threading, then tighten using a 12mm socket.
• Torque to 21 Nm (15 ft-lbs) using a foot-pound torque wrench.

Step 9: Reinstall the throttle body with a new gasket

• Install a new throttle body gasket and position the throttle body.
• Install fasteners using a 10mm socket, then Torque to 10 Nm (89 in-lbs).
• Plug the throttle body connector back in until it clicks.

Step 10: Reconnect hoses, reinstall intake tube, and reconnect the battery

• Reconnect all labeled hoses and connectors (match your tape labels).
• Reinstall the air intake tube and tighten the clamps using a flathead screwdriver.
• Reconnect the negative battery terminal using a 10mm socket.

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✅ After Repair

• Start the engine and let it idle for 2-3 minutes. It may idle slightly different at first after the throttle body was unplugged.
• Listen for hissing (vacuum leak). If you hear it, shut off and recheck hose connections and plenum seating.
• Road test for 10-15 minutes. Confirm no shaking, no loss of power, and no flashing check-engine light.
• If the check-engine light stays on, a scan may be needed to clear codes after the misfire is fixed.

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💰 DIY vs Shop Cost

Shop Cost: $350-$900 (parts + labor)

DIY Cost: $60-$540 (parts only, depending on 1 coil vs all 6)

You Save: $290-$360+ by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.5-3.0 hours.

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🎯 Ready to get started?

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