How to Tell If the Coil Pack on Your Car is Failing

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Identify and fix a faulty ignition coil with this DIY guide

Co-authored by Charley Helvy and Mason Martinez, BA

Last Updated: March 23, 2024 Fact Checked

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Symptoms

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Replacing a Bad Coil Pack

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What do ignition coils do?

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Why do ignition coils fail?

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Can you drive with a bad coil pack?

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Video

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Expert Q&A

A vehicle’s coil pack, also known as the ignition coil, supplies the high-tension current needed to bring your car to life. Even though coil packs last as long as 100,00 miles, temperature and friction can create cracks in their cylinders, making your car underperform and consume more gas. Do these symptoms sound familiar? Refer to this guide to learn how to replace your engine’s coils and keep your car running smoothly!

Common Signs of a Bad Engine Coil

Your car jerks, sputters or makes a loud banging sound.
Your vehicle consumes more fuel and requires more fill-ups.
Your car operates on less power, making it sluggish or stall out.

Section 1 of 5:

Symptoms of Bad Coil Pack

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1
Check Engine Light Ignition coil packs, or single coils (depending on your vehicle's make and model), are on top of the engine block in most modern cars. When your coil misfires or is faulty, it can be enough to trigger the Check Engine Light on your dashboard. This light can range from minor to major issues, so it's always best to pull over and get it checked immediately.
- Newer car models have Check Engine lights in different colors to help you understand the severity of the problem. A flashing or red light is a sign to take your car in immediately. Meanwhile, a solid yellow or orange may indicate more minor issues, like a loose gas cap.^{[1]
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Misfiring engine If you notice a jerking or sputtering feeling when driving at average speeds, this is one of the critical signs of an engine misfire. It can also include a coughing or consistent vibration when it's parked, idling, or while you're driving.
- Gasoline cars have an internal combustion engine ignited by a spark from the spark plugs. When your car misfires, one of the cylinders isn't working correctly.^{[2]
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Poor gas performance Are you having to fill up on gas more often? This could be an indication of a bad coil pack. With every misfire, the more fuel that's being used and lost. In turn, your vehicle's combustion efficiency drops, leading to increased emissions.^{[3]
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- High emissions are not only bad for your car but the environment, too.^{[4]
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Have you tried accelerating on the highway but felt your car sputtering or struggling to catch up to speed? This may be a result of a failing ignition coil. Leaving the issue unaddressed can cause significant damage to the engine, such as overheating or misfires, and cause an accident.
A backfire is a loud bang that results in power loss. The loud bang signals that unburned fuel suddenly escaped the exhaust system. This happens when the vehicle's internal combustion system isn't working correctly.^{[5]
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Is your car taking longer to start or has difficulty turning on in cold weather? This is a common issue in older vehicles with high mileage or single ignition coils. Coils connect to the spark plugs, which are required to make a spark that powers the car.^{[6]
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Section 2 of 5:

How to Replace a Damaged Ignition Coil

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1
Disconnect the car battery's negative cable. Before tinkering under your vehicle's hood, turn the ignition off. It's best to allow the engine to cool down to avoid accidentally burning yourself. To avoid electrical mishaps, take a 10-millimeter open-end wrench to unbolt the negative "-" cable.^{[7]
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- If your vehicle has plastic caps covering the battery terminals, remove them so you can unbolt the cable.
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Locate the ignition coil. On older vehicles made before the 1990s, ignition coils are found between the battery and a distributor. However, in modern cars, the coil is attached to the top of each pair of spark plugs, located near the top of the engine, and bolted into the cylinder head.^{[8]
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- In some vehicles, spark plugs may be hidden by wires or a plastic cover. Refer to your owner's manual for the exact placement.
First, squeeze the electrical plastic pigtail connector and pull it towards you. Then, use an open-ended wrench to remove the bolts. Set the bolts to the side. With your hand, remove the ignition coil by twisting it in a counter-clockwise position. Once it's loose, you can pull the coil out.^{[9]
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Apply di-electric grease to the new coil. To protect against corrosion and ensure good condition, add a dab of di-electric grease to the bottom of the new coil and its electrical socket. Use your finger or a clean microfiber cloth to distribute the grease evenly.^{[10]
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- Some ignition coils come pre-greased, so refer to the product's packaging for more information.
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Slide the new coil into its housing. The same way you pulled the old coil out, slide the new coil into its place with your finger. You should feel it sit around the spark plug. Rescrew the bolt to keep the coil in place and reattach the pigtail connector. You'll hear a click when it's connected.^{[11]
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- If replacing more than one coil, replace each one at a time to ensure you're not confusing the oil coils with the new ones.
- After the coil is successfully attached, you can start your car to ensure it's working correctly.

Section 3 of 5:

What do ignition coils do?

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A standard car's battery contains 12 voltages, which works to keep all of the electrical components functioning. That doesn't seem like a lot of power to start a car, does it? Well, that's where the ignition coil pack comes in. This small device transforms the battery's output into 45,000 volts! When it reaches this high-tension current, all the power transfers to the engine's spark plugs that get the car started.^{[12]
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Section 4 of 5:

Why do ignition coils fail?

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A vehicle's ignition coil fails after 80,000 to 100,000 miles. The more you use your vehicle, the more it heats up, and two things these coils hate are heat and vibration. Over time, the temperature and vibration can damage the coils, creating cracks that allow moisture to seep in.^{[13]
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- Similarly, coil failure can be caused by damaged spark plugs or wires with excessive gaps, making it harder for the coils to connect.

Section 5 of 5:

Can you drive with a bad coil pack?

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It’s possible to drive your vehicle with a failed coil, but beware—it’s generally unadvisable since it’s unsafe and damages your engine the longer you leave it unaddressed. For vehicles with a single ignition coil, though, your car might not start, so driving it isn’t an option anyway. If you’re going to drive, stick to local roads and only get behind the wheel when it’s absolutely necessary until you can see a mechanic.

Expert Q&A

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Question

How can I prolong the life of the ignition coil?

Charley Helvy
Automotive Expert
Charley Helvy is an Automotive & Diesel Expert based in Avondale, Arizona. He is the founder of Charley’s Garage, an educational YouTube channel focusing on simple videos for automotive and truck enthusiasts. He has over 31 years of experience in the automotive world. He is a Diesel Instructor at the Universal Technical Institute and is a certified ASE Master Heavy Truck Technician. He offers training on gas and diesel engines on his YouTube channel, along with other DIY and explanation videos for beginners and enthusiasts alike. In 2024, he published a complete guide on Emissions Systems in Automotive and Diesel Vehicles.

Charley Helvy

Automotive Expert

Expert Answer

Proper care for the ignition coil in your car involves several important steps. Firstly, conduct regular inspections to check for any signs of damage, corrosion, or wear on the ignition coil. Keep the electrical connections clean and free from dirt or corrosion, ensuring optimal conductivity. Additionally, maintain the battery voltage within the manufacturer's recommended range to prevent undue strain on the ignition coil. Replace worn or fouled spark plugs as needed to prevent excess workload on the ignition coil. Ensure proper engine cooling to prevent overheating of the ignition coil. Handle the ignition coil with care during maintenance tasks to avoid damage. Adhere to the recommended maintenance schedule outlined in your owner's manual, including checks and replacements of ignition system components.

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