🔧 Ignition Coil Replacement - Repair

Your Sierra uses coil-on-plug ignition coils, one on each spark plug. Replacing a bad coil can fix misfires, rough idle, hesitation, and check engine lights. On this truck, the job is straightforward, but you need to work carefully around the valve covers and spark plug wires/connectors.

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

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⚠️ Safety & Precautions

• Let the engine cool completely before starting. Coils and plugs can be very hot.
• Disconnect the negative battery cable before unplugging coils.
• Do not pull on the wiring; always release the connector lock first.
• If replacing one coil, inspect the spark plug on that cylinder too. A bad plug can damage a new coil.
• A misfire can create fuel smell and a hot catalytic converter. Avoid long idle or driving time if the engine is shaking badly.

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🔧 Required Tools

You'll need the following tools for this repair:

• 10mm socket
• Ratchet
• 6-inch extension
• Torque wrench
• Flat-blade screwdriver
• Needle-nose pliers
• Dielectric grease
• Shop rags
• Safety glasses
• Mechanic gloves

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Ignition coil - Qty: 1 per failed cylinder
• Ignition coil bolt - Qty: 1 per coil if damaged or rusted
• Engine cover grommets - Qty: as needed if cracked
• Spark plug - Qty: 1 per cylinder serviced, if needed

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📋 Before You Begin

• Park on level ground and set the parking brake.
• Make sure the ignition is OFF and the key is removed.
• Disconnect the negative battery cable before touching coil connectors.
• If the engine cover is installed, remove it first.
• Replace the plug if it is worn or fouled.

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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

• Pull up gently by hand to release the cover from its mounting studs.
• If it feels stuck, wiggle it side to side instead of forcing it.

Step 3: Access the ignition coil

• Locate the coil on the valve cover at the cylinder you are servicing.
• Unplug the electrical connector by pressing the lock tab and pulling straight back.
• Never yank the harness.

Step 4: Remove the coil

• Use a 10mm socket and ratchet to remove the coil retaining bolt.
• Lift the coil straight up and off the spark plug tube.
• If it is stuck, twist it gently by hand before pulling it free.

Step 5: Inspect the spark plug well

• Look for oil, water, or debris inside the plug tube.
• If dirt is present, clean it out with shop rags or compressed air before installing the new coil.
• If the plug is being replaced, remove it now with the proper spark plug socket.

Step 6: Install the new ignition coil

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

Step 7: Reconnect the electrical connector

• Push the connector on until the lock clicks into place.
• Gently tug it once to make sure it is locked.

Step 8: Reassemble and restore power

• Reinstall the engine cover by pressing it down onto the mounting points.
• Reconnect the negative battery cable with a 10mm socket.

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✅ After Repair

• Start the engine and let it idle.
• Check for rough running, flashing check engine light, or new misfire symptoms.
• If the light was on before, clear the codes with a scan tool and recheck after a short test drive.
• If the same misfire returns on the same cylinder, inspect the spark plug, injector, and wiring.

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💰 DIY vs Shop Cost

Shop Cost: $180-$450 per coil replacement

DIY Cost: $40-$120 per coil

You Save: $140-$330 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 0.6-1.2 hours.

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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! Check out the parts and tools sections below to add everything to your cart.