🔧 Forester - Ignition Coil Replacement

Replacing the ignition coils on your Forester means removing the coil-on-plug units from the top of the spark plugs and installing new ones. A failing coil can cause misfires, rough idle, poor power, flashing check engine light, or fuel economy loss.

Difficulty Level: Beginner | Estimated Time: 1-2 hours

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⚠️ Safety & Precautions

• ⚠️ Work only on a completely cool engine. The exhaust and cylinder heads sit close to the coils and can burn you.
• ⚠️ Disconnect the negative battery cable before unplugging ignition coils to reduce the chance of electrical shorts.
• ⚠️ Do not pull on wiring. Release each connector tab first, then pull the connector body.
• ⚠️ If the check engine light is flashing, avoid driving until repaired because raw fuel can damage the catalytic converter.
• ⚠️ Your Forester has a horizontally opposed engine, so the coils are on the left and right sides of the engine bay, not on top like many vehicles.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 3/8-inch ratchet
• 3/8-inch short extension
• 3/8-inch universal joint
• Torque wrench rated 5-30 Nm
• Flathead screwdriver
• Needle-nose pliers
• Trim clip removal tool
• Work light
• Safety glasses
• Nitrile gloves

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Ignition coil - Qty: 1-4
• Dielectric grease - Qty: 1 small tube

Tip: If one coil failed from age, replacing all four can prevent repeat labor.

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📋 Before You Begin

• 🚗 Park your Forester on level ground, shift into neutral, and set the parking brake.
• 🧊 Let the engine cool for at least 30-60 minutes before working near the cylinder heads.
• 🔋 Use a 10mm socket to loosen the negative battery terminal, then move the cable aside so it cannot spring back.
• 🧠 If replacing only one coil, match the replacement to the cylinder shown by the trouble code. Cylinder numbering on this engine is: front passenger side #1, rear passenger side #3, front driver side #2, rear driver side #4.
• 📸 Take a phone photo before unplugging anything. This helps with routing connectors during reassembly.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Disconnect the Battery

• Use a 10mm socket and 3/8-inch ratchet to loosen the negative battery terminal clamp.
• Lift the negative cable off the battery post and place it where it cannot touch the terminal.
• Black cable is negative.

Step 2: Remove the Engine Cover if Equipped

• If your Forester has a plastic engine cover, use a 10mm socket to remove the retaining bolts.
• Lift the cover straight up and set it aside.
• Some Forester X models may not have a decorative engine cover.

Step 3: Create Working Space on the Passenger Side

• Use a flathead screwdriver or trim clip removal tool to release any plastic clips holding intake snorkel pieces in the way.
• Use a 10mm socket to remove any intake duct fasteners blocking access to the passenger-side ignition coils.
• Move the ducting aside carefully. Do not force plastic parts when cold.
• More room makes this much easier.

Step 4: Locate the Ignition Coils

• Use a work light to look at the side of each cylinder head.
• Each ignition coil is a small rectangular unit with an electrical connector and one mounting bolt.
• The coils plug directly onto the spark plugs. This is called “coil-on-plug,” meaning there are no traditional spark plug wires.

Step 5: Unplug the Coil Connector

• Press the locking tab on the ignition coil connector with your thumb or a flathead screwdriver.
• Pull the connector straight back by the plastic connector body.
• If the connector is stuck, use needle-nose pliers gently on the connector body, not the wires.
• Never pull the wires.

Step 6: Remove the Ignition Coil Bolt

• Use a 12mm socket, 3/8-inch ratchet, and 3/8-inch short extension to remove the coil mounting bolt.
• On tight rear coils, use a 3/8-inch universal joint. A universal joint is a swivel adapter that helps the socket turn at an angle.
• Set the bolt aside where it cannot fall into the engine bay.

Step 7: Remove the Old Ignition Coil

• Grip the ignition coil firmly by hand and twist it gently left and right.
• Pull the coil straight out from the spark plug tube.
• If it feels stuck, keep twisting gently while pulling. Do not pry hard against the plastic coil body.
• Inspect the rubber boot for oil, cracks, white tracking marks, or swelling.

Step 8: Prepare the New Ignition Coil

• Apply a very thin film of dielectric grease inside the rubber boot opening.
• Dielectric grease is a non-conductive silicone grease that helps seal out moisture and makes future removal easier.
• Do not pack the boot full of grease. A tiny amount is enough.
• Too much grease can cause misfires.

Step 9: Install the New Ignition Coil

• Push the new ignition coil straight into the spark plug tube by hand.
• You should feel the boot seat onto the spark plug.
• Align the coil mounting ear with the bolt hole.
• Install the mounting bolt by hand first to avoid cross-threading.

Step 10: Tighten the Ignition Coil Bolt

• Use a 12mm socket, 3/8-inch short extension, and torque wrench rated 5-30 Nm to tighten the coil bolt.
• Torque to 6.4 Nm (57 in-lbs).
• Do not overtighten. The bolt threads into aluminum, which can strip if forced.

Step 11: Reconnect the Coil Connector

• Push the electrical connector onto the ignition coil until it clicks.
• Gently tug the connector body by hand to confirm it is locked.
• Repeat Steps 5-11 for each ignition coil being replaced.

Step 12: Reinstall Intake Ducting and Cover

• Use a 10mm socket to reinstall any intake duct fasteners removed earlier.
• Use a trim clip removal tool or your fingers to reinstall plastic clips.
• If equipped, reinstall the engine cover using a 10mm socket.
• Torque small 10mm cover/intake fasteners snug only, about 3-5 Nm (27-44 in-lbs).

Step 13: Reconnect the Battery

• Place the negative battery cable back onto the battery post.
• Use a 10mm socket and 3/8-inch ratchet to tighten the clamp.
• Torque to 5 Nm (44 in-lbs).
• Make sure the cable cannot twist by hand after tightening.

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✅ After Repair

• ✅ Start the engine and let it idle for 2-3 minutes.
• ✅ Listen for smooth idle. A steady idle means the coils and connectors are likely seated correctly.
• ✅ If the engine misfires or shakes, shut it off and recheck that every coil connector clicked into place.
• ✅ If you have a scan tool, clear any stored misfire codes after the repair.
• ✅ Test drive gently for 10-15 minutes and confirm there is no flashing check engine light.
• ✅ If oil was found inside a spark plug tube, the valve cover tube seals may also need repair.

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💰 DIY vs Shop Cost

Shop Cost: $220-$650 (parts + labor, depending on whether 1 or all 4 coils are replaced)

DIY Cost: $45-$320 (parts only, depending on coil brand and quantity)

You Save: $150-$330 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 0.8-1.5 hours.

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🎯 Ready to get started?

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