How Do Ignition Coils Work?

March 20, 2025

5 min read

March 20, 2025

5 min read

Ignition coils - opens in new window or tab. convert the low-voltage electricity from your car’s battery into the high voltage needed to ignite the gasoline in the engine. The ignition coils power the spark plugs and must be replaced periodically to ensure optimum running.

Let’s dive deeper into these components to learn the signs of a failing coil, how often coils should be replaced, and the average cost.

What Ignition Coils Do

Ignition Coil Conversion Kit RED Plug Wires 2004-11 Mazda RX-8. — Ignition coils feed electricity to the spark plugs. This Mazda RX-8 kit includes spark plug wires.

Ignition coils take the electrical voltage from the car’s battery and boost it to a level that can power the spark plugs. Because the spark plug ignites the air/fuel mixture in the cylinders, the ignition coils must supply adequate voltage for proper engine performance, emissions, and fuel efficiency.

An ignition coil contains primary and secondary coils which wrap around a magnetic core. The primary coil receives 12 volts from the battery. The secondary coil transmits between 12,000 and 45,000 volts of power to the spark plugs. Current flowing into the primary coil creates a magnetic field. When that current is interrupted (either by the ignition control module in modern cars or the distributor in older vehicles), the magnetic field collapses and generates a high-voltage transmission in the secondary coil that’s sent to the spark plugs to ignite the air/fuel mixture.

Today’s ignition coils are often part of a coil-on-plug (COP) assembly, one for each cylinder. This newer configuration improves the efficiency of the system and reduces the need for wires. Older models have a coil pack design, where one coil transmits power to every spark plug.

How Long Do Ignition Coils Last?

An old rusty ignition coil sitting on a dusty engine. — When an ignition coil goes bad, replacement is an easy task.

Ignition coils are considered consumable and are not meant to last the lifetime of the vehicle. On average, coils last between 60,000 and 100,000 miles. A few factors affect how often you should replace your ignition coils.

Vehicle make/model: Some vehicles need ignition coil replacement more frequently. This depends on how new the vehicle is, what type of ignition coil system it uses, and the engineering of the system.

Driving conditions: Stress from taking frequent short trips, driving in extreme temperatures, or constant stop-and-go traffic can all reduce the ignition coil’s lifespan.

Brand/quality: The quality of the ignition coils plays a huge role in how long they will last. Just like spark plugs and brakes, cut-price ignition coils might have a much shorter life compared to high-quality items.

Maintenance: Regular maintenance helps keep ignition coils in good shape. Replacing your spark plugs at regular intervals can extend the life of the ignition coil. You should immediately address electrical issues that cause voltage irregularities before the condition damages the ignition coils.

Signs of a Bad Ignition Coil

An illuminated Check Engine light. — If your vehicle’s check engine light is illuminated, it’s time to plug in an OBDII code scanner.

There’s no reason to replace a functioning ignition coil before symptoms appear. As a coil starts to fail, you’ll notice engine performance issues.

Among the top symptoms is trouble starting the engine. A crank-no-start condition or hard starting indicates a weak spark from the coil. Once the engine is running, misfires due to a lack of a strong spark also signal a coil problem. Hesitation, poor acceleration, or rough running while idling are all signals of a bad coil. A bad ignition coil may also lead to backfiring exhaust.

Any of these symptoms could cause the check engine light to illuminate, and fuel efficiency will decrease.

How long can you drive on a bad ignition coil?

We don't recommend driving with a bad ignition coil. But we also understand it might not be possible to fix the problem immediately.

In the short term, driving with a bad coil will be unpleasant due to the performance problems listed above. Long-term, a bad ignition coil could cause catalytic converter - opens in new window or tab. damage due to unburned fuel entering the exhaust. Bottom line: Replace a bad ignition coil as soon as you can.

Ignition Coil Replacement Cost

An EMPI ignition kit for Type 1 VW engines with a distributor, ignition coil, and spark plug wires. — Ignition coils can be purchased as part of an ignition kit.

Replacing an ignition coil may cost as little as $15 to $100 if you’re replacing a single coil and doing the work yourself. If your vehicle has coil packs, you may spend between $30 and $300 doing it yourself, depending on how many coils are included with the pack. The make and model of your vehicle will influence the price, as will your choice of original equipment (OEM) or aftermarket replacement parts.

If you aren’t able to replace the coil yourself, a shop may charge for one to two hours of labor per coil. With an average labor rate between $75 and $150 per hour, the cost could go up significantly. Additionally, if you have a luxury vehicle, you may need to pay more for a mechanic who specializes in that brand.

Replacing Your Ignition Coils

A vehicle owner installs a new ignition coil in an inline four-cylinder engine. — Installing new ignition coils is a simple task for most do-it-yourselfers.

In most vehicles, it’s not difficult to replace ignition coils - opens in new window or tab. . With the right tools, you can have the new coil installed in less than 30 minutes. You’ll need to disconnect the battery and wiring harness, then remove the coil fasteners and the coil before replacing it with a new one. The rest of the job is simply putting everything back together again.

Should you replace all your ignition coils?

There’s no rule that you need to replace all ignition coils at the same time. If you have one bad coil, it’s acceptable to replace it alone. However, if you are replacing the coil because of age, it’s likely the others aren’t performing well. If you’re experiencing widespread symptoms and degraded engine performance, you should swap all of the coils at the same time.

You may also consider installing new spark plugs if it’s time, giving the vehicle a full tune-up. This ensures that your entire ignition system is working like new, giving you the best possible power and efficiency.

About the author

Mike Bumbeck

Mike has written about vintage automobiles and the people behind them for more than two decades. His experience includes writing for Hot Rod, Hemmings, and Mecum Auctions—and working on the pit crew of a nostalgia top fuel dragster. He lives in New England with a multi-vehicle fleet that ranges from a contemporary front-wheel-drive turbo hatchback to vintage Japanese 4x4s. His hobbies include building, flying, and crashing remote control scale model airplanes.

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This article is meant to provide general guidance only. Automotive maintenance, repair, upgrade, and installation may depend on vehicle-specifics such as make and model. Always consult your owner's manual, repair guide for specific information for your particular vehicle and consider a licensed auto-care professional's help as well, particularly for advance repairs.