🔧 Outback - Spark Plug Replacement

On your Outback, the spark plugs sit on the sides of the flat (boxer) engine, so access is tight and you’ll remove a few nearby parts to reach the ignition coils and plugs. Replacing worn plugs helps prevent misfires, rough idle, and poor fuel economy.

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

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⚠️ Safety & Precautions

• 🧤 Work on a fully cool engine to avoid burns and prevent thread damage in the cylinder head.
• 🔋 Disconnect the negative battery terminal before unplugging ignition coils.
• 👓 Support the hood securely and keep loose clothing away from the cooling fans.
• ⚠️ Do not use anti-seize on Subaru’s plated spark plug threads unless the plug maker specifically requires it.

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🔧 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
• 3/8" extension set 3" and 6"
• 3/8" wobble extension
• 3/8" universal joint
• 14mm thin-wall spark plug socket
• Flathead screwdriver
• Needle-nose pliers
• Flashlight

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Iridium spark plugs - Qty: 4
• Dielectric grease - Qty: 1

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📋 Before You Begin

• 🅿️ Park on level ground, shift to Park, and set the parking brake.
• 🧊 Let the engine cool completely (cold to the touch).
• 🔋 Open the hood and disconnect the battery negative terminal using a 10mm socket.
• 💡 Know the parts: the ignition coil is the small module bolted to each plug, with an electrical connector.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover (if equipped)

• Pull up firmly at the corners to pop the cover off its rubber grommets.
• Use a flashlight to locate the ignition coils on each side of the engine.

Step 2: Create access to the passenger-side spark plugs (air intake/air box area)

• Loosen the intake hose clamp(s) using a flathead screwdriver.
• Unclip and lift the air box lid/ducting out of the way as needed (use needle-nose pliers for stubborn clips).
• Take a quick photo before disassembly.

Step 3: Create access to the driver-side spark plugs (battery area)

• Remove the battery hold-down using a 12mm socket.
• Disconnect the battery terminals using a 10mm socket and lift the battery out carefully.
• Set the battery somewhere stable and upright.

Step 4: Remove one ignition coil (do one plug at a time)

• Press the lock tab and unplug the coil electrical connector by hand (use a flathead screwdriver gently only if needed).
• Remove the coil retaining bolt using a 10mm socket.
• Twist the coil slightly, then pull it straight out.

Step 5: Remove the old spark plug

• Install the 14mm thin-wall spark plug socket onto a 3/8" extension set 3" and 6" as needed.
• If the angle is tight, switch to a 3/8" wobble extension or 3/8" universal joint.
• Break the plug loose with the 3/8" ratchet, then unthread it fully and remove it.

Step 6: Install the new spark plug

• Start threading the new plug by hand using the spark plug socket and extension only (no ratchet at first).
• If it doesn’t spin in smoothly, back it out and try again to avoid cross-threading.
• Once seated, tighten with a 3/8" torque wrench: Torque to 21 N·m (15 ft-lbs).
• Iridium plugs are typically pre-gapped.

Step 7: Reinstall the ignition coil

• Apply a tiny smear of dielectric grease inside the coil boot.
• Push the coil straight onto the new plug until fully seated.
• Install and tighten the coil bolt using a 10mm socket: Torque to 6.4 N·m (57 in-lbs).
• Reconnect the coil electrical connector until it clicks.

Step 8: Repeat for the remaining 3 spark plugs

• Repeat Steps 4–7 on the other cylinder on that side, then move to the opposite side.
• Keep bolts and parts grouped by side to avoid mix-ups.

Step 9: Reinstall removed components

• Reinstall the air intake/air box parts and tighten clamps using a flathead screwdriver.
• Reinstall the battery and hold-down using a 12mm socket.
• Reconnect battery terminals using a 10mm socket (negative terminal last).
• Reinstall the engine cover by pressing it back onto the grommets.

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✅ After Repair

• 🔍 Start the engine and let it idle for 1–2 minutes. It should run smooth with no shaking.
• 🛠️ If you have a scan tool, check for misfire codes and clear any stored codes after confirming the fix.
• 👂 Listen for hissing (intake leak) and re-check air intake clamps if idle is rough.
• 🚗 Take a short test drive and confirm normal power and no check-engine light.

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💰 DIY vs Shop Cost

Shop Cost: $350-$650 (parts + labor)

DIY Cost: $60-$140 (parts only)

You Save: $210-$590 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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