🔧 CX-5 - Spark Plug Replacement

This is a straightforward job: remove the engine cover and ignition coils, then replace all four spark plugs. Mazda schedules replacement on this non-turbo engine at 75,000 miles (120,000 km). mazdausa.com

Difficulty Level: Beginner | Estimated Time: 1-1.5 hours

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⚠️ Safety & Precautions

• ⚠️ Let the engine become completely cold before removing the plugs. The cylinder head is aluminum, and hot threads damage easily.
• 🧤 Wear gloves and safety glasses when using compressed air.
• 🔑 Keep the ignition switched off and the key away from the vehicle.
• 🚫 Never allow dirt, tools, or loose hardware to fall into a spark-plug opening.
• 🔌 Battery disconnection isn’t normally required for this repair.
• 🧴 Don’t put anti-seize on the new plug threads unless the plug manufacturer specifically requires it.

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🔧 Required Tools

You'll need the following tools for this repair:

• 8mm socket
• 14mm thin-wall spark plug socket
• 3/8-inch drive ratchet
• 3/8-inch drive 6-inch extension
• 3/8-inch drive inch-pound torque wrench
• 3/8-inch drive foot-pound torque wrench
• 0.040-inch wire spark plug gap gauge
• Compressed-air blow gun
• Clean shop towels
• Nitrile work gloves
• Safety glasses

A spark plug socket is a deep socket with a rubber or magnetic insert that holds the plug securely.

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Vehicle-matched long-life iridium spark plugs - Qty: 4

Mazda specifies genuine-equivalent long-life plugs for the SKYACTIV-G 2.5. Replace all four together, and don’t clean old iridium plugs with a wire brush because it can damage their fine electrode coating. mazdausa.com

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📋 Before You Begin

• 🅿️ Park your CX-5 on level ground, select Park, and apply the parking brake.
• ❄️ Allow the engine to cool for at least two hours, preferably overnight.
• 🧹 Clean loose dirt from around the top of the engine before opening any plug well.
• 📦 Keep the new plugs in their protective sleeves until each one is installed.
• 📏 Confirm each replacement plug matches the listing and isn’t visibly damaged.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover

• Grip the plastic engine cover near its mounting points with both hands.
• Pull straight upward to release the cover from its rubber grommets.
• Place it somewhere clean where it won’t be stepped on.

Step 2: Clean around the ignition coils

• Use the compressed-air blow gun while wearing safety glasses.
• Blow dirt away from all four ignition coils and plug wells.
• Don’t continue until the top of the engine is clean.

Step 3: Disconnect the first ignition coil

• Press the locking tab on the electrical connector and pull the connector straight back.
• Pull on the connector body, not the wires.
• If the tab is stubborn, press the connector inward first, then depress the tab.

Step 4: Remove the first ignition coil

• Use the 8mm socket, extension, and ratchet to remove the coil retaining bolt.
• Twist the coil gently to release its rubber boot, then pull it straight upward.
• Inspect the boot for cracks, oil, rust-colored tracking, or burned marks.
• Do one cylinder at a time.

Step 5: Clean the spark-plug well

• Use the compressed-air blow gun to remove dirt from inside the empty well.
• Make sure nothing remains around the plug before loosening it.

Step 6: Remove the old spark plug

• Lower the 14mm thin-wall spark plug socket and 6-inch extension onto the plug.
• Attach the ratchet and turn counterclockwise to loosen the plug.
• Once loose, remove the ratchet and spin the extension by hand.
• Lift the plug out with the spark plug socket.

Step 7: Inspect the old spark plug

• A dry tan or light-gray tip is generally normal.
• A wet oily plug can indicate oil entering the cylinder.
• A fuel-wet or heavily blackened plug can indicate an ignition or mixture problem.
• If one plug looks dramatically different, keep it labeled by cylinder for later diagnosis.

Step 8: Check the new spark plug

• Compare the new and old plugs for matching thread diameter, thread length, and seat design.
• Use the 0.040-inch wire spark plug gap gauge only to verify the supplied gap.
• Don’t force a flat coin-style gauge between fine-wire iridium electrodes.
• Don’t bend the center electrode. Fine-wire tips are delicate.

Step 9: Hand-start the new spark plug

• Place the new plug in the 14mm spark plug socket.
• Use only the extension, without the ratchet, to lower it into the well.
• Turn clockwise by hand until the plug seats.
• If it doesn’t turn smoothly, back it out and restart it. Never force it.
• Hand-threading prevents an expensive cylinder-head repair.

Step 10: Torque the new spark plug

• Attach the 3/8-inch drive foot-pound torque wrench.
• Torque the spark plug to 15-20 Nm (11-15 ft-lbs).
• Use the replacement plug manufacturer’s stated torque if its instructions specify a narrower value.
• Don’t add another turn after the torque wrench clicks. More isn’t better here.

Step 11: Reinstall the ignition coil

• Push the ignition coil straight over the spark plug until the boot is fully seated.
• Install the coil bolt by hand first.
• Use the 3/8-inch drive inch-pound torque wrench and 8mm socket.
• Torque the ignition-coil bolt to 8-10 Nm (71-89 in-lbs).
• Reconnect the electrical connector until its lock clicks.

Step 12: Replace the remaining three plugs

• Repeat Steps 3 through 11 for each remaining cylinder.
• Keep each plug well closed until you’re ready to work on it.
• Confirm every coil bolt and connector is installed before moving on.

Step 13: Reinstall the engine cover

• Inspect the rubber mounting grommets and ensure they’re seated correctly.
• Align the cover over its mounting studs.
• Press directly above each mounting point until the cover snaps into place.

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✅ After Repair

• 🔍 Count four connected coil plugs and four installed coil bolts.
• 🚗 Start the engine and let it idle for two minutes.
• 👂 Listen for a smooth idle without shaking, tapping, or misfiring.
• ⚠️ If the check-engine light flashes, shut the engine off immediately and recheck every coil connector.
• 🧪 Take a short test drive, then confirm the engine still idles smoothly.
• 💻 No infotainment reset, battery registration, or programming is required.

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💰 DIY vs Shop Cost

Shop Cost: $180-$350 (parts + labor)

DIY Cost: $45-$120 (parts only)

You Save: $60-$230 by doing it yourself!

Shop labor rates vary by area. This repair takes a shop approximately 0.7-1.0 hour.

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🎯 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! The spark-plug aisle is open for your CX-5, so you can choose four matched plugs and the correct 14mm socket.