7 Symptoms of a Bad Coil Pack and the Cost of Replacement (2023)

The coil pack is an essential part of the ignition system. It works hand in hand with the spark plugs to burn the air-fuel mixture in the engine. If a coil pack breaks, you'll know it, even if you're not a professional technician. The symptoms will be impossible to ignore.

In this guide, we look at the main symptoms of a bad coil pack. We also explain its function and show you where to find it. Finally, we look at how much coil pack replacement can cost and answer your top questions about this system.

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Symptoms of a bad coil pack

If the coil pack is bad, you can expect the check engine light to come on and probably blink. The engine may also misfire and fuel consumption increases. There is also rough idling, problems accelerating, changing engine noise and possible fuel smell.

Many of these symptoms appear whenever there is an engine problem. Because of this, you cannot use just one symptom to determine if there is a problem with the coil pack. Let's take a closer look at these symptoms of a bad coil pack to see what you might be dealing with.

1. Engine misfire

7 Symptoms of a Bad Coil Pack and the Cost of Replacement (1)

Oair-fuel mixturein a gasoline engine, proper ignition is necessary for the engine to run smoothly. If the ignition pack does not work as it should, this mixture cannot ignite.

The result is amisfire engineit sounds like the unit is stuttering or shaking. When you stop at a traffic light, the misfire can be so severe that the engine shakes and vibrates.

2. Brilliant engine control

7 Symptoms of a Bad Coil Pack and the Cost of Replacement (2)

OCheck engine lightis designed to let you know if something is wrong with the engine. All modern cars are equipped with a self-diagnosis system known as OBD-II. If an engine sensor detects that something is operating outside of normal parameters, the Check Engine Light will come on and a code will be set in the system. If there is a serious problem, thethe light will blink, prompting you to stop driving before engine failure occurs.

You can use a compatible scanner to read the engine sensor trouble codes to determine what is wrong. It is possible for your vehicle to give a P0351 code, which indicates problems with the ignition system. You may also see a code related to engine misfire.

3. Increased fuel consumption

7 Symptoms of a Bad Coil Pack and the Cost of Replacement (3)

Ignition coils can spontaneously fail or break over time. As they wear out, your car's fuel economy will gradually decline. Using a fuel consumption calculator, you can keep an eye on your car's fuel consumption to identify when there is a problem.

Even if you find out that the fuel economy is related to some other mechanical issue, you'll be glad you noticed. After all, no one wants to spend money on gas.

4. Slow walking

7 Symptoms of a Bad Coil Pack and the Cost of Replacement (4)

Any mechanical malfunction that does not ignite the air-fuel mixture can causeSlow march. For this reason, coil packs must be taken into account.

Along with coil packsclogged air filter,faulty spark plugsEdirty injectorscould also be the culprit. Therefore, it is not possible to diagnose the problem based on this symptom alone.

5. Gross acceleration

The same goes for acceleration issues. While this is a symptom of a bad coil pack, it can also be the cause of most engine malfunctions.

If the power drops when you step on the accelerator, something is wrong and must be addressed immediately. If you allow the problem to persist, the vehicle may stall.

6. Changed engine sound

7 Symptoms of a Bad Coil Pack and the Cost of Replacement (5)

Earlier we talked about an engine with a misfire. This symptom also comes with some strange noises that you might not be used to. If the engine jolts and jolts, you will hear a louder noise.

If the coil pack is bad, it can cause the engine to run less than normal on one or more cylinders, causing the engine sound to change.

In extreme cases, the car can also backfire. This loud popping noise occurs whenever unburned fuel escapes from the exhaust. Not only do you want to fix this to prevent further damage, but also to avoid the noise embarrassment.

7. Fuel smell

If the fuel mixture is not burning properly, you may smell gasoline. However, ignition problems are not the only reason for this symptom.

In fact, the gasoline smell is mostly related to the fuel system or exhaust. If you're having this symptom with some of the others we've mentioned, it could be caused by the coils or spark plugs.

What is the function of a coil pack?

7 Symptoms of a Bad Coil Pack and the Cost of Replacement (6)

Coil sets work in conjunction with thespark plugs. To create a spark, there must be a high voltage supply for the fuel in the cylinder to ignite. At the start of combustion, the coil pack is responsible for accumulating the corresponding amount of energy. Sometimes this is between 50,000 and 75,000 volts.

The electronic control module or computer sends the signal to the ignition controller to release voltage from the coil pack. That voltage travels to the spark plugs, where the spark can jump and ignite the fuel-air mixture in the cylinder chamber.

Where is the coil pack?

7 Symptoms of a Bad Coil Pack and the Cost of Replacement (7)

Today's gas powered engines often use independent coil systems known as coil on plug. This coil is placed individually over each spark plug. So if you have an eight cylinder engine with eight spark plugs, you probably also have eight coils.

However, older engines used a different coil design equipped with coil packs. Instead of one coil for each spark plug, there would be a coil pack for multiple spark plugs. For example, an eight-cylinder engine might have four sets of coils, one for every two spark plugs.

Coil sets can be placed anywhere on the engine. Each model does this differently. Often these coil assemblies are in a different location than the spark plugs, requiring a wire to connect the two. If you trace the wire coming out of the spark plug, you can find the coil pack connected to it.

The disadvantage of coil packs is that if one coil fails, the entire pack must be replaced. The packages are molded together and cannot be separated.

How much does it cost to replace a coil pack?

On average, expect to spend between $250 and $450 to replace a coil pack. This estimate includes parts and labor for a standard car. Prices may vary depending on where you live, type of vehicle and number of coils to be replaced.

Also, you might want to replace the spark plugs at the same time. If it's almost time to replace them as part of your regular maintenance, you can do it while you're already working on the car.

Being able to do some of this work yourself will also save you some money. On some vehicles, replacing the coil packs is easy with a few basic mechanic tools.

Interestingly, the price of replacing a coil pack is often higher than replacing the coil plug on newer models. Since this system handles multiple spark plugs, it is, of course, more expensive. Also, they can be harder to find since they are on older vehicles. You may need to order your coil packs online if your local auto parts store doesn't carry them.

coil test

You can test coil packs yourself to see if they fail. We recommend buying ainstruction manualfor your vehicle so that you can compare the measured values ​​with the manufacturer's specifications. Specifications vary by coil type, but here are some general recommendations.

Follow these steps.

  1. Find the coil pack. We show the location above.
  2. Remove the spark plug wires from the clamp. Use a ratchet and a socket wrench or spanner to remove the package.
  3. use amultimeterread ohms. Set it to 200 ohms.
  4. Connect the multimeter to the appropriate terminals.
  5. Test the coil pack for continuity. Most coils have continuity between 0.3 ohms and 1.0 ohms.

Next you want to check the coil pack for secondary resistance.

  1. Set your multimeter to the 20,000 ohm range.
  2. Place the probes on the appropriate terminals. There is a protruding tower that connects the secondary winding to the ignition coil.
  3. You should see a reading between 5,000 and 12,000 ohms. The value can be between 5.0 and 12.0.
  4. An O.L reading indicates that there is an open loop in the circuit.

If the readings do not match what is in the manual, consider replacing the coil pack. Also, you can check the engine for codes to see what faults were detected. You can have several problems at the same time.

common questions

Can you drive with a faulty coil pack?

You will still be able to operate the vehicle, but we do not recommend driving it. Not only will there be performance issues that can cause a crash due to the unpredictability, but it's also possible to screw up other important parts. For example, the catalytic converter will eventually fail after driving your car this way.

How often do coil packs need to be replaced?

Most manufacturers do not have a recommended maintenance interval for coil assemblies. This older technology isn't used in today's vehicles, so you should only replace it when necessary. Most coil packs are expected to last at least 100,000 trouble free miles.

What causes damage to the coil pack?

Wear and tear is the most common cause of failure. Years of abuse are taking their toll on the ignition coils. Also, engine and driving vibrations can cause the insulation to crack, resulting in a short circuit in the electrical connection.

Are coil packs the same as spark plugs?

Many online sources will tell you that spark plugs and coils are the same thing, but this is not true. The coils supply the voltage to the spark plugs. On modern engines, there is one ignition coil for each spark plug, while older vehicles often use a coil pack for multiple spark plugs.


The car's ignition system is fascinating and we still marvel at it today after working on vehicles for many years. When everything is going as it should, it's like a well-oiled machine with everything in place and doing its job. On the other hand, if something doesn't work during operation, everything seems to go downhill.

Coil packs may not be a huge part of the car, but they serve an important purpose. Without them doing their job, the engine's overall performance suffers. If you notice problems with your coil packs, if your fuel economy has dropped, or your engine is misfiring, it's time to get it checked before bigger problems arise.



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