Warning Signs of a Bad Ignition Coil: What Every Driver Needs to Know

Are you noticing symptoms of a bad ignition coil in your car? Ignition coil failure can cause serious issues if not addressed.  Knowing the signs of a bad ignition coil can help you diagnose and address any potential problems with your car’s engine. 

Ignition coils play a crucial role in the functioning of your vehicle’s engine. They are responsible for converting the battery’s voltage into the high voltage needed to create a spark that ignites the fuel in the engine’s combustion chamber. Over time, ignition coils may experience wear and tear and, eventually, fail.

If the ignition coil fails, it can cause difficulty starting the engine, engine misfires or stalls, decreased fuel efficiency, rough idling or vibrations, and the illumination of the check engine light. Drivers should be aware of these warning signs to ensure their safety on the road.

In this article, we’ll discuss the symptoms of a bad ignition coil and how to tell if yours is malfunctioning. 

What Causes Ignition Coils to Fail?

Sometimes it’s hard to pin down exactly what causes ignition coils to wear out over time, but there are a few likely culprits. The ignition coils in your car may fail before their time if the fuel-to-air ratio is too heavy or too lean. 

If your car has 80,000 to 100,000 kilometers on it, you probably won’t need to replace the ignition coil until then. If you want your ignition system to last as long as possible, one thing you can do is maintain its components.

What are the Signs of a Faulty Ignition Coil?

Signs of a Bad Ignition Coil

A car’s ignition coil is responsible for amplifying the weak current coming from the battery to a level high enough to spark the fuel and get the motor going. However, problems with the vehicle’s mechanics or performance can be brought on by a faulty ignition circuit. That’s why we’re going to go over in more depth the signs that point to a bad ignition coil:

Difficulty Starting the Engine

An ignition coil is responsible for converting the low voltage generated by the car’s battery into the thousands of volts that are required to ignite a mixture of air and fuel in the combustion chamber of the car.

If you find it difficult to start your engine, one of the most likely causes is a bad ignition coil. When your ignition coil fails, you may notice symptoms such as an engine cranking but not starting or taking longer than usual to start.

Engine Misfires or Stalls

If you’re experiencing symptoms of a bad ignition coil, such as engine misfires or stalls, it is important to investigate the issue promptly.

As a result of a faulty ignition coil, the spark plug may not be able to receive the required voltage, which can result in the engine misfiring. While driving, you may experience a loss of power, a feeling of hesitation, or a jerking sensation. The engine may even stall completely in some cases, leaving you stranded in the middle of nowhere.

There are also instances when faulty ignition coils can increase emissions levels to such an extent that emissions testing may fail and potential repair costs could incur.

To ensure that your vehicle remains reliable and safe on the road, make sure to have any symptoms of a bad ignition coil inspected by a qualified mechanic right away!

Decreased Fuel Efficiency

If you’re getting less mileage out of a full tank than normal, it could be an indication that your ignition coil is failing. The ignition coil is in charge of supplying the required voltage to the spark plugs, which ignite the fuel in the combustion chamber of the engine. If the ignition coil fails to provide enough voltage, the spark plugs will not correctly ignite the fuel. As a result, fuel efficiency suffers, resulting in higher fuel usage and lower gas mileage.

A faulty ignition coil can cause the engine to fail or hesitate, reducing fuel economy. When the engine malfunctions, it does not burn all of the fuel in the combustion chamber, resulting in wasted fuel and lower gas economy. Furthermore, if the ignition coil fails, the system may attempt to compensate by injecting more fuel into the engine, which can reduce your car’s fuel economy even further.

Fuel leakage can also indicate a faulty ignition circuit. Incomplete combustion can result from a failing ignition coil, resulting in gasoline leaks from the engine. This is a severe problem that necessitates immediate attention from a qualified mechanic. If you detect a fuel leak, do not drive your vehicle because it is extremely dangerous.

It’s essential to note, however, that poor fuel economy can also be caused by other issues, such as a faulty mass airflow (MAF) sensor or a dirty engine air filter. The MAF sensor determines the proper fuel-to-air ratio for efficient combustion by measuring the amount of air entering the engine. A faulty MAF sensor can result in a decline in fuel efficiency. A dirty engine air filter, on the other hand, can restrict airflow to the engine, resulting in decreased fuel economy.

Rough Idling or Vibrations

In addition to poor fuel efficiency and engine misfires, another common symptom is rough idling or vibrations when the vehicle is at a stop.   This can occur when the ignition coil fails to supply a consistent spark to the spark plugs, leading to irregular combustion and a rough idle as a consequence. If you sense your vehicle shaking or vibrating while it is idling, this may be an indication that the ignition coil needs to be replaced.

 When you step on the accelerator to increase speed, a failing ignition coil may not provide enough voltage to the spark plugs, causing them to misfire. This can result in a hesitation or jerking sensation when accelerating, which can be especially noticeable at low speeds or when starting from a stop.

It is essential to address any problems with the ignition coil as soon as possible in order to prevent more expensive repairs in the future. 

If the indications of a faulty ignition coil are ignored, it is possible to cause damage to other components of the engine, including the catalytic converter, which can be a costly component to replace.

Illumination of the Check Engine Light

An illuminated Check Engine Light can indicate a variety of problems with your vehicle, including possible ignition coil problems. Your car’s computer is continuously monitoring various sensors and systems to ensure that everything is functioning properly. When something goes wrong, a warning light on the dashboard, in this instance, the Check Engine Light, will illuminate.

If the computer discovers a problem with the ignition coils, it will frequently illuminate the Check Engine Light. Misfires, which occur when the spark plugs do not receive enough power to ignite the fuel in the engine, are one of the most frequent problems with ignition coils, and misfires will cause the computer to trip and turn on the Check Engine Light, notifying you to the problem.

Aside from misfires, the Check Engine Light can illuminate if the computer senses a problem with the ignition coil signal or circuit. For example, if a coil burns out or shorts, it can disrupt the transmission to the computer, triggering the caution light. The computer may also identify other ignition coil-related issues, such as a faulty sensor or a wiring problem.

If the Check Engine Light illuminates, it is critical to have the computer scanned for trouble codes as soon as feasible. This enables a trained mechanic to diagnose the problem and determine whether it is caused by the ignition coils or another component. Ignoring the warning light can lead to more severe problems later on, such as engine damage and decreased performance.

How Do You Replace A Damaged Ignition Coil?

It is easy to replace a broken ignition coil, especially if your car has a plug-and-play coil design. In this case, even a first-time do-it-yourselfer should be able to handle the replacement without help from a pro. But some coils might be hard to get to, so you might need help from a mechanic.

If you replace the ignition coil yourself, you’ll save money on labor, but you’ll have to pay for the new part, which can cost anywhere from $40 to $300, depending on the make and model of your car.

If you choose to have a mechanic replace the ignition coil, you’ll have to pay for both the parts and the labor, which can vary depending on how the engine is built and where the broken coil is. Overall, replacing a broken ignition coil as soon as possible can help keep you from having to make bigger and more expensive repairs down the road.

Read also: The Ignition Coil Change-up: Why Your Car Won’t Start


The symptoms of a bad ignition coil are often easy to identify and diagnose, as they may cause your vehicle to run rough or fail to start. If you think something is wrong with your car, you should look for signs of a bad coil. If you don’t, this could cause serious damage over time. If you notice any of the above problems, you should take your car to a professional mechanic as soon as possible to avoid any more problems.

So keep an eye out for these signs because they could save you time, money, and trouble later on.

More resources: Maximizing Your Coil Change: Actionable Steps for Optimal Performance

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