🔧 Spark Plugs - Replacement

Replacing the spark plugs on your Altima helps restore smooth starts, proper fuel economy, and clean engine performance. The 2.5L inline-4 uses four spark plugs located under the ignition coils on top of the engine.

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

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⚠️ Safety & Precautions

• ⚠️ Let the engine cool completely before starting. Spark plugs thread into aluminum cylinder head material, which can be damaged when hot.
• ⚠️ Disconnect the negative battery terminal to reduce the chance of accidental electrical shorts.
• ⚠️ Work on one spark plug at a time so dirt cannot fall into multiple open plug wells.
• ⚠️ Do not over-tighten spark plugs. Over-tightening can damage the cylinder head threads.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 3/8-inch drive ratchet
• 3/8-inch drive 6-inch extension
• 14mm thin-wall spark plug socket
• 3/8-inch drive torque wrench
• Flat-blade screwdriver
• Compressed air blow gun
• Needle-nose pliers
• Clean shop towels
• Nitrile gloves
• Safety glasses

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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 small tube

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📋 Before You Begin

• Park your Altima on level ground and set the parking brake.
• Turn the ignition off and remove the key or keep the key fob away from the vehicle.
• Open the hood and let the engine cool until it is safe to touch.
• Disconnect the negative battery terminal using a 10mm socket. The negative terminal is marked with a minus sign.
• A spark plug socket is a deep socket with a rubber insert or magnet that holds the spark plug while you lift it out.
• A torque wrench is a tool that tightens bolts or spark plugs to an exact tightness so parts are not damaged.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the Engine Cover

• Use both hands to lift the plastic engine cover straight upward from the top of the engine.
• If it feels stuck, gently work one corner at a time by hand. Do not pry hard with a screwdriver.
• Set the cover aside on a clean surface.
• Pull upward, not sideways.

Step 2: Locate the Ignition Coils

• Look across the top of the engine for four black ignition coils.
• Each ignition coil has an electrical connector and one small retaining bolt.
• An ignition coil is the part that sends high voltage to the spark plug.

Step 3: Disconnect the First Ignition Coil Connector

• Start with the coil closest to one end of the engine.
• Use your thumb to press the connector release tab, then pull the connector straight back.
• If the connector is tight, use a flat-blade screwdriver gently on the release tab only.
• Do not pull on the wires.
• Connector plastic can be brittle.

Step 4: Remove the First Ignition Coil

• Use a 10mm socket, 3/8-inch drive ratchet, and 3/8-inch drive 6-inch extension to remove the coil retaining bolt.
• Twist the ignition coil gently by hand, then pull it straight upward.
• Place the coil on a clean shop towel in the same position it came from.

Step 5: Clean the Spark Plug Well

• Put on safety glasses.
• Use a compressed air blow gun to blow dirt and grit out of the spark plug well.
• The spark plug well is the deep tube where the spark plug sits.
• Keep your face away from the area while using compressed air.

Step 6: Remove the Old Spark Plug

• Place the 14mm thin-wall spark plug socket onto the 3/8-inch drive 6-inch extension and 3/8-inch drive ratchet.
• Lower the socket straight down onto the spark plug.
• Turn counterclockwise slowly to loosen the spark plug.
• Once loose, continue turning by hand with the extension until the plug is free.
• Lift the spark plug out carefully using the spark plug socket.
• If the plug does not come out with the socket, use needle-nose pliers gently on the metal top only.

Step 7: Inspect and Start the New Spark Plug

• Compare the old spark plug to the new iridium spark plug. The thread length and connector end should match.
• Do not adjust the gap on fine-wire iridium plugs unless the plug manufacturer specifically says to do so.
• Insert the new spark plug into the 14mm thin-wall spark plug socket.
• Lower it straight into the spark plug well.
• Turn the extension clockwise by hand only for several turns.
• If it does not turn smoothly by hand, remove it and start again. This prevents cross-threading, which means damaging the threads by starting the plug crooked.
• Hand-start every spark plug.

Step 8: Tighten the New Spark Plug

• Attach the 3/8-inch drive torque wrench to the 14mm thin-wall spark plug socket and extension.
• Tighten the spark plug to Torque to 20 Nm (15 ft-lbs).
• Stop as soon as the torque wrench clicks.
• Do not add anti-seize unless the spark plug manufacturer requires it. Most modern iridium spark plugs have plated threads.

Step 9: Reinstall the Ignition Coil

• Apply a tiny amount of dielectric grease inside the rubber boot of the ignition coil.
• Dielectric grease helps seal out moisture but does not conduct electricity.
• Push the ignition coil straight down onto the new spark plug until fully seated.
• Install the coil retaining bolt using the 10mm socket, 3/8-inch drive extension, and 3/8-inch drive torque wrench.
• Tighten the ignition coil bolt to Torque to 7 Nm (62 in-lbs).

Step 10: Reconnect the Ignition Coil Connector

• Push the electrical connector straight onto the ignition coil by hand.
• Listen or feel for a small click.
• Lightly tug the connector to make sure it is locked.

Step 11: Repeat for the Remaining Spark Plugs

• Repeat Steps 3 through 10 for the other three ignition coils and spark plugs.
• Use the 10mm socket for each coil bolt.
• Use the 14mm thin-wall spark plug socket for each spark plug.
• Tighten each spark plug to Torque to 20 Nm (15 ft-lbs).
• Tighten each ignition coil bolt to Torque to 7 Nm (62 in-lbs).

Step 12: Reinstall the Engine Cover and Battery Cable

• Line up the engine cover with its mounting points.
• Press the cover straight down by hand until seated.
• Reconnect the negative battery terminal using a 10mm socket.
• Tighten the battery terminal snugly. Do not over-tighten it.

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✅ After Repair

• Start your Altima and let it idle for 1-2 minutes.
• The engine should idle smoothly with no shaking or flashing check engine light.
• If the idle is rough, turn the engine off and recheck that all four ignition coil connectors are fully clicked in.
• Take a short test drive and listen for smooth acceleration.
• If the battery was disconnected, the clock, radio presets, and one-touch window settings may need to be reset.

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💰 DIY vs Shop Cost

Shop Cost: $220-$380 (parts + labor)

DIY Cost: $45-$100 (parts only)

You Save: $120-$280 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 0.8-1.2 hours.

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