🔧 Ignition Coils - Replacement

The ignition coils on your Sierra sit on top of each spark plug and turn battery voltage into the high voltage needed to fire the plugs. If a coil fails, you may get a misfire, rough idle, poor fuel economy, or a check engine light.

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

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⚠️ Safety & Precautions

• Let the engine cool completely before starting. Coils sit on a hot engine.
• Ignition systems can produce high voltage. Do not touch coil terminals with the engine running.
• Disconnect the negative battery cable before unplugging or removing coils.
• Keep dirt out of the spark plug wells. Contamination can cause misfires.
• If a coil boot is stuck to the spark plug, remove it carefully to avoid tearing it.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• 1/4-inch ratchet
• 1/4-inch extension
• Trim removal tool
• Small flathead screwdriver
• Torque wrench
• Dielectric grease
• Safety glasses
• Nitrile gloves

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Ignition coil - Qty: 1 per failed cylinder, or 6 to replace all
• Coil boot - Qty: 1 per coil if separate from the coil
• Spark plug - Qty: 6 if you choose to replace them at the same time

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📋 Before You Begin

• Park on level ground and set the parking brake.
• Let the engine cool fully.
• Disconnect the negative battery cable before touching the coils.
• Work on one coil at a time so you do not mix up connectors.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Disconnect battery power

• Use a 10mm socket to remove the negative battery cable from the battery.
• Move the cable aside so it cannot spring back and touch the terminal.

Step 2: Remove the engine cover if equipped

• Lift the engine cover straight up by hand.
• If it feels stuck, use a trim removal tool to gently free it.

Step 3: Access the ignition coils

• Locate the coil you want to replace on top of the engine.
• Press the connector lock tab and unplug the electrical connector from the coil.
• Use a small flathead screwdriver only if the connector lock is tight. Do not pry hard.

Step 4: Remove the coil

• Use a 10mm socket and 1/4-inch ratchet to remove the coil retaining bolt.
• Pull the coil straight up and out of the spark plug well.
• Torque spec for installation: 10 Nm (89 in-lbs).

Step 5: Inspect the spark plug well

• Look for oil, water, or dirt in the plug tube.
• If present, clean it out before installing the new coil.
• Clean wells help new coils last longer.

Step 6: Install the new coil

• Apply a small amount of dielectric grease inside the coil boot if needed.
• Slide the new coil straight down onto the spark plug.
• Install the coil bolt by hand first, then tighten with the 10mm socket.
• Torque to 10 Nm (89 in-lbs).

Step 7: Reconnect the coil harness

• Push the electrical connector onto the coil until it clicks.
• Gently tug it once to make sure it is locked.

Step 8: Repeat for any other coils

• Repeat the same steps for each failed coil.
• If the truck has high mileage, replacing all 6 coils at once can prevent repeat failures.

Step 9: Reinstall engine cover and battery cable

• Reinstall the engine cover by pressing it into place.
• Reconnect the negative battery cable and tighten it with the 10mm socket.

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✅ After Repair

• Start the engine and let it idle.
• Make sure the idle is smooth and the check engine light is off.
• If the truck still misfires, scan for codes and check the spark plug on that cylinder.
• If the misfire moved with the coil, the coil was the problem.

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💰 DIY vs Shop Cost

Shop Cost: $250-$700 (parts + labor)

DIY Cost: $60-$300 (parts only)

You Save: $190-$400 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1-2 hours.

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🎯 Ready to get started?

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