What Happens When an Ignition Coil Fails?

The ignition coil may not be the most well-known part under your hood, but it plays a critical role in your engine’s ability to run smoothly. This component transforms the battery’s low voltage into the high-voltage spark needed to ignite the air-fuel mixture in each cylinder. Without properly functioning ignition coils, your engine simply won’t run the way it should.

If one or more ignition coils fail, you may experience a range of symptoms from mild performance issues to a car that won’t start at all. Here’s what you need to know about how ignition coils work, what happens when they fail, and how to address the issue before it leads to bigger problems.

What Does the Ignition Coil Do

Each ignition coil is connected to a spark plug. It takes the 12 volts from your car battery and amplifies it to several thousand volts—enough to create a spark across the gap of the spark plug. This spark ignites the fuel-air mixture inside the combustion chamber.

Some vehicles have a single coil that distributes voltage to all the spark plugs, while modern vehicles often have one coil per cylinder. If your vehicle has six cylinders, it likely has six individual coils.

Signs of a Failing Ignition Coil

One of the most common signs of a bad ignition coil is engine misfiring. When a coil isn’t sending voltage to its spark plug, that cylinder can’t fire properly, which throws off the rhythm and efficiency of the engine. Symptoms can include:

Rough idling or vibrations when the engine is running
Decreased fuel economy
A noticeable loss of power during acceleration
The check engine light coming on
Engine hesitation or stalling
Difficulty starting the car

These signs often come on gradually but can worsen quickly. A failing ignition coil puts extra stress on other engine components, including the catalytic converter.

What Causes an Ignition Coil to Go Bad

Ignition coils are subject to wear over time, especially as they endure constant temperature fluctuations under the hood. Common causes of failure include:

Heat and vibration damage
Oil or coolant leaks contaminate the coil
Moisture intrusion from cracked seals or old spark plug boots
Faulty spark plugs cause the coil to work harder than it should
General age and mileage

If your vehicle has high miles and still has the original coils, they’re likely due for inspection or replacement.

Can You Drive With a Bad Ignition Coil

Technically, you might still be able to drive with a failing coil, especially if your vehicle has multiple coils and only one is malfunctioning. But it’s not a good idea. When your engine misfires, unburned fuel can enter the exhaust system, which leads to overheating and eventual damage to your catalytic converter—an expensive component to replace.

A misfiring engine may produce more emissions, cause poor fuel economy, and leave you at risk of a sudden breakdown. The longer you wait, the greater the damage and the more costly the repairs.

Diagnosing the Problem

If your check engine light is on and you suspect a coil issue, a professional diagnostic scan can identify which cylinder is misfiring. From there, a technician can test the coil using specialized tools to determine if it's sending the correct voltage.

In some cases, technicians may swap coils between cylinders to see if the misfire follows the coil. If it does, that’s a strong indication that the coil is the problem.

Should All Coils Be Replaced at Once

If your vehicle has individual ignition coils and only one is faulty, it might seem cost-effective to replace just that one. However, if your vehicle has high mileage, the others may not be far behind. Many drivers choose to replace all coils at once to avoid repeat visits to the shop and ensure consistent performance.

Some manufacturers even recommend changing all the coils during a major tune-up, especially when replacing spark plugs or valve cover gaskets.

Keep Your Engine Running Strong With AutoCraft in Spokane Valley, WA

If you’ve noticed hesitation, rough running, or the dreaded check engine light, don’t wait to have your ignition system inspected. Our skilled technicians can diagnose ignition coil issues and perform efficient, high-quality replacements using trusted parts.

Call AutoCraft in Spokane Valley, WA, today to schedule a diagnostic. Let us keep your engine running smoothly, reliably, and ready to perform.

Visit one of our AutoCraft locations today for reliable service and peace of mind.