12 bad ignition coil symptoms

As time passes and the mileage on your car increases, some parts might wear out and completely fail. It includes parts like the catalytic converter or the ignition coil. In that case, you must look for specific symptoms and know when to replace them. In the ignition system, the ignition coil supplies the necessary current to ignore the fuel mixture in the combustion chamber.


The most common symptoms of a bad ignition coil are the engine light coming on and a rough start. Replacing a bad ignition coil costs between $20 and $40.

Here’s a list of the things we’ll look at:

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The ignition coil is essential for the proper functionality of your car. A bad or failing ignition coil will prevent your car from starting. Therefore it is a serious problem. In modern cars, each spark plug has its ignition coil, some of which are electronically controlled by the central computer.

Because they are so important, you must pay attention to their condition more often. In this article, we will show you 12 overheating ignition coil symptoms to look for while also informing you about the replacement cost in case they are broken. 

16 Ford Transit 150 was ignition coils

Symptoms of a bad ignition coil

While a skilled mechanic can diagnose your car and identify the problem accurately, you can also do the same at home without the help of any special tools. All you have to do is a minimal investigation and specific focus on a certain problem.

If you suspect that the ignition coil is failing, there are a couple of symptoms you can look for and identify if your car has a problem.

Here are some of the symptoms of a bad ignition coil we’ll take a look at:

  • Worn cables
  • The check engine light coming on
  • Poor acceleration
  • Rough start
  • Stalling

1. Excessive heat

Ignition coils are exposed to extreme heat from the engine since they are situated so close to it. All the plastic and metal components of the coils are constantly suffering from the heat generated by the engine. 

When affected by heat, the metallic components will constantly expand. It reduces the ability to transform low voltages into high voltages. Over time your ignition coil might fail due to excessive heat. 

2. Excessive vibrations

Besides heat, the engine also produces significant vibrations when running. If you are driving off-road or on a bumpy surface, the vibrations are accentuated. The effects on the ignition coil are worse. Because they are installed above the spark plugs, they are sensitive to intense vibrations.

Over time, the connections in the coil assembly will inhibit the current flow between the components of the coil. That is why you must bring your car to an auto repair shop every once in a while for a proper check-up and diagnosis. 

Toyota Camry ignition coil

3. Moisture and contamination

Moisture and contamination can often cause wear. Because these are installed in the engine, they will get contaminated if oil and coolant leak into the engine block. Moisture can also corrode or short the electrical components of these parts, causing them to malfunction.

If you notice leaks in the engine block, you must fix this problem as soon as possible. Not only your ignition coils are at risk, but your entire engine might be compromised if exposed to excessive moisture. 

4. Excessive spark plug gap

Several conditions have to be met for the ignition coils to function properly. One of them requires that the current from the coils must bridge the gap between the plug electrodes. It will generate the spark by the spark plug and allow you to turn on your engine quickly.

But they will have to work harder if the gap is wider than recommended. Because there is an additional effort to produce a current strong enough to reach the increased gap, the coil components are stressed and can wear more quickly. 

5. Worn cables

It is an older technology that you will find in some outdated vehicles. Special ignition cables deliver the current from coils to the spark plugs. Sometimes they can get damaged due to the excessive heat inside the engine block.

Over time, these cables will go bad and lose their resistance. If not replaced consistently, these cables could also burn out the ignition coil and further increase the repair cost. 

BWM ignition coil

6. The check engine light is on.

It is the easiest way to spot something wrong with your car. When the check engine light turns on and is visible on the dashboard, then it is a clear warning sign that there is something wrong with a component of the engine. 

The onboard computer will monitor the vehicle’s systems and signal you when the ignition coils are damaged or failing. As a result, the check engine light turns on and asks you to investigate the problem. 

7. Rough start

This part is directly responsible for turning on your engine. If this part fails, you will notice that the engine will struggle upon starting. In some cases, it won’t be able to start. 

A significant amount of energy is delivered from the battery for starting your engine. Ignition coils are critical in meeting this high energy demand. But if the ignition coils are damaged or failing, you will often experience rough starts

8. Poor acceleration

There are many reasons why you might experience poor acceleration when you press on the gas pedal. Faulty sensors and an incorrect fuel supply are some of them. 

You should also consider the spark plugs and ignition coils to be the reason for your problem. If these parts are failing, the engine will hesitate with the acceleration process. You will be able to notice a significant delay in throttle response. 

9. Stalling

When the engine is stalling, there is something likely wrong with the ignition coil. It can be caused by several issues, such as insufficient air or failure of combustion. 

They are responsible for providing the necessary voltage to create a spark. When this operation cannot be done, the engine will shut down because it cannot produce enough propelling force. 

ignition coil

10. Misfires

This symptom is similar to stalling, where the engine misfires can be linked with bad or failing coils. Suppose there is a combustion failure in the engine’s cylinders. In that case, your car will behave differently. The engine will misfire more often. 

These are easy to notice because they make a well-known sputtering sound that can identify. If you can hear any uncommon noise coming from the engine block, you should have your car checked by a mechanic. 

11. Backfires

As a result of misfires that happen inside the combustion chamber, the backfires will happen outside the cylinders. When ignition coils are worn out or damaged, it always leads to failure in the ignition in at least one cylinder.

But if the fuel mixture leaves this chamber unburnt, it might combust in the exhaust system and create a backfire. This backfire can severely damage the entire exhaust system, so it is not something to ignore.

12. Poor fuel economy


As incomplete combustion leaves the extra fuel unburnt, you might experience poor fuel economy. It’s another symptom of bad ignition coils. When they cannot provide enough voltage to the spark plugs, the fuel will not be converted into a usable mixture.

As a result, the fuel consumption might be higher with a broken ignition coil than it was before this part failed. In the long term, your budget will be affected by the increased fuel costs, and you will also have to refuel more often. 

Replacement cost

Whether you own a small-sized city car or a large vehicle like the Dodge Ram 1500, replacing the coil packs will take some money out of your wallet. You will only have to replace the coil pack if it goes bad. The retailers that sell them often offer better deals for buying them in packs.

Usually, you should expect to pay between $20 to $40 for a single ignition coil. Unless you replace this part yourself, you also have to consider the labor costs and the extra fees demanded by the auto repair shop. 

Here’s the cost of other basic maintenance work.

MaintenanceFrequencyExpected cost ($)
Basic inspectionEvery 5,000 miles200
Tire rotationEvery 8,000 miles70
Wiper replacementEvery six months$20
Brake pad replacementEvery 20,000 miles$200

What are coil packs & what do they do?

For optimal engine performance, new vehicles must rely on sensors that constantly communicate the data gathered to the engine control unit. As a result, this control unit will be able to make adjustments and ensure a better driving experience.

The ignition coils form a coil pack that transforms power from the battery into usable electrical energy. It generates a spark that helps each cylinder fire individually and allows your engine to function properly. These parts can also create a cleaner combustion process since no moving parts are involved. 

How can you tell if they’ve gone bad?

Ford focus

You can test the coil pack with a special tool called a multimeter. It measures Ohm’s resistance, and you can find the proper resistance for the coil’s windings. With that information, you are able to proceed and find potential problems. 

The ignition coils have two separate coils named primary winding and secondary winding. With such a performant tool, you must connect the multimeter’s positive and negative leads to the terminal. Remember that they vary from model to model, so you should check the owner’s manual for more information.

The reading on the multimeter will give you a result to compare with the specifications mentioned by the car manufacturer. If this reading is not within the optimal resistance range, you will need to replace it. We also found the best multimeter for you, so you won’t have to search the market for hours. 

AstroAI Multimeter 2000 Counts Digital Multimeter

This versatile and highly accurate digital multimeter can measure the voltage and resistance of various parts. This useful tool is intended for both commercial and personal use, and you can also use it on your household electrical systems. 

With a fast sampling speed of 2 times per second, this multimeter is superior compared to other models. The LCD display will display the results. They are visible even in dark environments or during conditions with low visibility.

The double ceramic fuse protects this tool from overloading, while a silicon cover will reduce damage if you drop this tool to the ground. Batteries power this device, and the display will inform you when the battery power is low. 

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Item Weight0.4 Pounds
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How to test them without a multimeter?

While a multimeter will give you accurate results, many more methods will help you test the coil pack. One of them implies unscrewing the coils and leaving them inside the cylinder. As you start the car, the engine will be running, and you can slowly remove one of the coils.

Once you remove it, place a test light in the hole that is holding this part. If it is not working, a constant spark will be produced that can be clearly visible. If the coil is bad or failing, this spark will be missing. You will have to replace the part. Be advised that this method is dangerous and you should wear protective equipment. 

How long do they usually last?

2007 lincoln

After you replace the coil packs with a brand new one, you should expect them to last up to 5 years. Depending on how frequently you drive your car, a coil pack replacement has to be done earlier than 5 years if you reach 120,000 miles. 

Even though coil packs are designed to last a long time, constant exposure to heat and friction can accelerate the wearing process. It is recommended that you check their condition from time to time. 

Spark plug vs. coil pack

These parts are both essential for your vehicle but are not the same. The ignition coil is located in the ignition system, and it helps create a spark that the spark plugs use to start the engine. 

The spark plug is responsible for supplying the spark that ignites the fuel mixture in the engine and starting the combustion process. This part helps with creating the necessary power to move your car. Spark plugs use up to 50,000 volts created by the ignition coil, so it is a complex part.

Have you noticed any of the following symptoms?

  • Excessive spark plug gap
  • Worn cables
  • Excessive vibrations
  • Excessive heat
  • Rough starts

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