🔧 Altima - Spark Plug Replacement

Changing the spark plugs on your Altima helps restore smooth idle, strong acceleration, and good fuel economy. On the V6 3.5L engine, the rear spark plugs sit under the upper intake plenum, so this job takes patience and careful reassembly.

Difficulty Level: Intermediate | Estimated Time: 2.5-4 hours

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⚠️ Safety & Precautions

• ⚠️ Let the engine cool completely before starting. The intake and cylinder heads can stay hot for a long time.
• ⚠️ Disconnect the negative battery cable before unplugging ignition coils and throttle body connectors.
• ⚠️ Keep dirt, bolts, and tools out of the intake ports. Anything dropped inside can seriously damage the engine.
• ⚠️ Do not force spark plugs. Cross-threading can damage the aluminum cylinder head.
• ⚠️ The throttle body may need idle air volume relearn if it is cleaned or disturbed heavily. Do not clean it unless needed.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 12mm socket
• 14mm socket
• 5/8-inch spark plug socket
• 3/8-inch drive ratchet
• 3/8-inch drive torque wrench
• 3-inch extension
• 6-inch extension
• 10-inch extension
• Universal joint socket adapter
• Flathead screwdriver
• Phillips screwdriver
• Needle-nose pliers
• Plastic trim removal tool
• Magnetic pickup tool
• Compressed air nozzle
• Spark plug gap gauge
• 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: 6
• Upper intake plenum gasket set - Qty: 1
• Throttle body gasket - Qty: 1

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📋 Before You Begin

• Park your Altima on level ground, shift to Park, and set the parking brake.
• Open the hood and let the engine cool fully.
• Use a 10mm socket to disconnect the negative battery cable, then move it aside so it cannot touch the battery post.
• Take photos of vacuum hoses, electrical connectors, and intake tube routing before removal. This helps a lot during reassembly.
• A plenum is the upper intake chamber that distributes air to the engine. It must be removed to reach the rear spark plugs.
• A torque wrench tightens bolts to a measured amount so small aluminum engine parts are not damaged.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the Engine Cover

• Use a 10mm socket to remove the engine cover fasteners, if equipped.
• Lift the cover straight up and set it aside.
• Keep bolts grouped by location.

Step 2: Remove the Air Intake Duct

• Use a flathead screwdriver to loosen the hose clamp at the throttle body.
• Use a flathead screwdriver to loosen the hose clamp at the air filter housing.
• Use needle-nose pliers to release any small hose clamps attached to the intake duct.
• Unplug the mass airflow sensor connector by pressing its tab with your fingers or a plastic trim removal tool.
• Lift the air intake duct out of the engine bay.

Step 3: Disconnect Hoses and Connectors from the Upper Intake Plenum

• Use needle-nose pliers to loosen and slide back the vacuum hose clamps on the upper intake plenum.
• Pull the hoses off gently by twisting them by hand. Do not yank on them.
• Use a plastic trim removal tool to release wiring clips attached to the plenum.
• Unplug the throttle body electrical connector by pressing the lock tab and pulling straight back.
• Use clean shop towels to label or separate hoses so they return to the same place.

Step 4: Remove the Upper Intake Plenum

• Use a 12mm socket, 3/8-inch drive ratchet, and extension to remove the upper intake plenum bolts and nuts.
• Use a 10mm socket to remove any small brackets attached to the plenum.
• Lift the plenum carefully. If it sticks, wiggle it gently by hand.
• Do not pry against sealing surfaces with a screwdriver.
• Once removed, place clean shop towels over the open intake ports immediately.
• Cover intake openings right away.

Step 5: Remove the Front Ignition Coils

• An ignition coil is the small electrical part sitting on top of each spark plug.
• Use a 10mm socket to remove the front ignition coil retaining bolts.
• Press each connector tab and unplug the ignition coil connectors by hand.
• Pull each ignition coil straight up with a gentle twisting motion.

Step 6: Remove the Rear Ignition Coils

• Use a 10mm socket with a 6-inch extension to remove the rear ignition coil retaining bolts.
• Unplug the rear ignition coil connectors by pressing the lock tabs.
• Pull the rear ignition coils straight out. Use a gentle twist if they feel stuck.
• Set all coils in order so each one can go back to the same cylinder.

Step 7: Clean Around the Spark Plug Wells

• Use a compressed air nozzle to blow dirt out of each spark plug well.
• Wear safety glasses while using compressed air.
• If debris remains, use a magnetic pickup tool carefully around the well.
• Do not let dirt fall into the cylinder when the spark plug is removed.

Step 8: Remove the Old Spark Plugs

• Use a 5/8-inch spark plug socket, 6-inch extension, and 3/8-inch drive ratchet to loosen each front spark plug.
• Use a 5/8-inch spark plug socket, 10-inch extension, and universal joint socket adapter for tighter rear plugs.
• Turn counterclockwise slowly until the spark plug is free.
• Lift the spark plug out with the spark plug socket.
• If a plug feels stuck, tighten it slightly, then loosen again slowly. Do not force it.

Step 9: Check and Install the New Spark Plugs

• Use a spark plug gap gauge to verify the gap is about 0.043 in / 1.1 mm, unless the plug maker says not to adjust pre-gapped iridium plugs.
• Start each new spark plug by hand using the 5/8-inch spark plug socket and extension only. Do not use the ratchet at first.
• Turn clockwise by hand until the plug seats fully. This prevents cross-threading.
• Use a 3/8-inch drive torque wrench and 5/8-inch spark plug socket to tighten each spark plug to Torque to 19.6 Nm (14 ft-lbs).
• Do not apply anti-seize unless the spark plug manufacturer specifically requires it.
• Hand-start every plug first.

Step 10: Reinstall the Ignition Coils

• Push each ignition coil straight down onto its spark plug until fully seated.
• Use a 10mm socket to install the ignition coil bolts.
• Tighten the ignition coil bolts to Torque to 7 Nm (62 in-lbs).
• Reconnect each ignition coil electrical connector until it clicks.

Step 11: Install New Intake Gaskets

• Remove the old upper intake plenum gaskets by hand or with a plastic trim removal tool.
• Use clean shop towels to wipe the gasket grooves and mating surfaces.
• Install the new upper intake plenum gasket set into the grooves.
• Install the new throttle body gasket if the throttle body was removed from the plenum.
• Do not use sealant unless the gasket instructions specifically call for it.

Step 12: Reinstall the Upper Intake Plenum

• Remove the shop towels from the intake ports. Count them to make sure none are missing.
• Set the upper intake plenum back into place carefully by hand.
• Use a 12mm socket and extension to start all plenum bolts and nuts by hand first.
• Use a 3/8-inch drive torque wrench to tighten the plenum fasteners in a crisscross pattern to Torque to 18 Nm (13 ft-lbs).
• Use a 10mm socket to reinstall any small brackets removed earlier.

Step 13: Reconnect Hoses and Electrical Connectors

• Reconnect all vacuum hoses by hand to their original locations.
• Use needle-nose pliers to slide hose clamps back into place.
• Reconnect the throttle body electrical connector until it clicks.
• Use a plastic trim removal tool to secure wiring clips back onto the plenum.

Step 14: Reinstall the Air Intake Duct

• Set the air intake duct between the air filter housing and throttle body.
• Use a flathead screwdriver to tighten both hose clamps snugly.
• Reconnect any small hoses using needle-nose pliers for the clamps.
• Reconnect the mass airflow sensor connector until it clicks.

Step 15: Reconnect the Battery and Final Check

• Use a 10mm socket to reconnect the negative battery cable.
• Check that no tools, rags, or loose bolts remain in the engine bay.
• Use a Phillips screwdriver or 10mm socket to reinstall the engine cover fasteners, if equipped.

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✅ After Repair

• ✅ Start the engine and let it idle. It may crank slightly longer on the first start.
• ✅ Listen for hissing sounds. A hiss can mean a vacuum hose or intake gasket is not seated correctly.
• ✅ Confirm the check engine light is off.
• ✅ Test drive gently for 10-15 minutes and verify smooth acceleration.
• ✅ If idle is unstable after battery disconnect or throttle body disturbance, an idle air volume relearn may be needed with a compatible scan tool.

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💰 DIY vs Shop Cost

Shop Cost: $450-$800 (parts + labor)

DIY Cost: $90-$220 (parts only)

You Save: $360-$580 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 2-3 hours.

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🎯 Ready to get started?

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