12 Common Symptoms Of A Bad Coil Pack & Replacement Cost!

Written By: Terrence Hines
Category: Engine

Symptoms of a bad coil pack can manifest in many forms, significantly impacting your vehicle’s performance and fuel efficiency.

Don’t ignore a faulty coil pack, leading to engine strain and expensive repairs. The average replacement cost is $120 to $350, so take proper action to save time and money.

10 Symptoms Of A Bad Coil Pack

A bad coil pack can harm your vehicle’s overall performance. When the coil pack fails, the ignition spark becomes weak or non-existent, resulting in an engine misfire.

This misfire can cause various issues, including a rough idle, stalling, poor acceleration, and even the check engine light activation.

In addition, the unburned fuel from the misfire can lead to decreased fuel efficiency, impacting your wallet at the pump.

It is important to promptly address these symptoms of a bad coil pack to prevent any additional harm to other engine components, including the catalytic converter.

Neglecting the issue can result in more costly repairs and compromise the safety and smoothness of your driving experience.

By taking action and resolving coil pack problems, you can ensure optimal performance, fuel efficiency, and a worry-free journey.

1. Lack Of Power:

One of the prominent symptoms of a bad coil pack is a noticeable lack of power.

This happens when the coil pack cannot generate enough spark for combustion, creating an engine performance imbalance.

12 Common Symptoms Of A Bad Coil Pack & Replacement Cost!

As a result, you may experience sluggish acceleration, reduced fuel efficiency, or a general sensation that your vehicle is not performing to its fullest potential.

In more severe cases, the engine might even misfire, causing your vehicle to jerk or vibrate during the ride, indicating a more significant issue with the coil pack.

It is important to address this problem promptly to ensure optimal engine performance and prevent further damage to your vehicle.

2. Dirty Exhaust Fumes:

Another telltale sign of a bad coil pack is the emission of dirty exhaust fumes or visible smoke from the tailpipe.

Under normal circumstances, the exhaust from your vehicle should be relatively clear, indicating a proper combustion process.

However, if your coil pack fails, it can lead to an incomplete combustion process, where the spark plugs cannot ignite the air-fuel mixture effectively.

This incomplete combustion can result in excess unburned fuel, which makes it out through the exhaust system.

This extra fuel can cause the emission of dark, foul-smelling smoke – a clear indication that your coil pack may need attention.

Observing these signs can help diagnose and address potential issues with your vehicle’s ignition system, ensuring optimal performance and fuel efficiency.

3. Engine Overheating:

Engine overheating is a common symptom and a problematic consequence of a malfunctioning coil pack.

Engine Overheating

When the coil pack is defective, it can strain the engine excessively, leading to overheating and a significant decline in the vehicle’s overall performance.

The intense heat generated can damage the engine’s intricate components, potentially resulting in costly repairs.

Moreover, the continuous overheating of the engine poses a serious hazard, escalating the risk of vehicle fires and jeopardizing safety.

Given these circumstances, promptly addressing signs of an overheating engine is crucial. They may indicate a faulty coil pack that needs immediate attention.

4. Erratic Engine Temperature Gauge Readings:

Erratic engine temperature gauge readings could also indicate a potential issue with the coil pack.

A faulty or malfunctioning coil pack can cause the temperature gauge on the dashboard to display unreliable fluctuations, compromising accurate temperature readings.

This occurs because the coil pack’s inefficiency can disrupt the engine’s temperature regulation, leading to inconsistent operating temperatures and gauge readings.

It is important not to overlook this symptom, as it could potentially signal a more serious underlying problem with the vehicle’s coil pack that requires attention.

5. Rough Idling:

Rough idling is also among the common symptoms of a bad coil pack.

When the coil pack is inefficient, it can cause the engine to run unevenly, resulting in an uncomfortable experience for the driver.

Imagine the feeling of running over small bumps on the road, but constant and persistent, causing significant discomfort and frustration.

Moreover, this rough idling affects the driving experience and can impact fuel efficiency, increasing fuel consumption and additional expenses.

Hence, having your vehicle examined by a professional if you observe this symptom is paramount.

This could signify a defective coil pack that demands immediate attention and repair to guarantee optimal engine performance and a seamless driving experience.

6. A Loud Knocking Sound From The Engine Bay:

A loud knocking sound from the engine bay could also signify a failing coil pack.

This sound is often produced when the spark plugs don’t receive the necessary current for combustion, causing the fuel to detonate at the wrong time.

This premature detonation, often called ‘knocking’ or ‘pinging,’ can cause severe damage to the engine’s internal components if left unchecked.

It’s important to note that a faulty coil pack can lead to decreased fuel efficiency and rough engine performance.

To identify potential coil pack failure, it is crucial to investigate any knocking sound from your engine and take appropriate action to prevent further damage.

12 Common Symptoms Of A Bad Coil Pack

Regular maintenance and timely replacement of faulty coil packs can help ensure your vehicle’s engine’s smooth functioning and longevity.

7. Check Engine Light Is On:

The illumination of the check engine light is one of the telltale symptoms of a bad coil pack. While various issues can trigger this light, a faulty coil pack is one of the common causes.

The vehicle’s onboard computer system can detect a failing coil pack and trigger the check engine light as a warning.

However, because the check engine light can indicate numerous different issues, it’s recommended to use an OBD-II scanner to retrieve the specific trouble code.

This can help pinpoint whether the coil pack is the actual source of the problem.

8. The Smell Of Fuel Or Burning Oil In The Vehicle:

The smell of fuel or burning oil in the vehicle is a symptom commonly associated with a bad coil pack.

A malfunctioning coil pack might fail to provide the necessary spark for combustion, causing unburnt fuel to be expelled from the exhaust.

This unburnt fuel can produce a strong gasoline smell, filling the vehicle’s cabin.

A failing coil pack could also lead to overheating, which can result in oil or other engine fluids burning off, leading to a distinct burning smell.

9. Poor Gas Mileage:

Poor gas mileage is another symptom that can indicate a faulty coil pack.

When the coil pack fails to provide an adequate spark, it leads to inefficient combustion, resulting in the engine consuming more fuel than necessary.

This inefficiency can significantly impact the vehicle’s miles per gallon (MPG) performance, leading to more frequent trips to the gas station.

Therefore, it is crucial to regularly monitor your vehicle’s gas mileage to detect any drastic changes that may highlight potential issues, including a failing coil pack.

By paying attention to this detail, you can address the problem promptly and maintain optimal fuel efficiency for your vehicle.

10. Misfires Or Backfiring While Driving:

Misfires or backfiring while driving are among the serious symptoms of a bad coil pack.

When the coil pack fails to deliver the necessary electric charge, the spark plugs cannot properly ignite the fuel-air mixture in the combustion chamber, causing the engine to misfire.

You might experience this as a sudden jolt or loss of power. Conversely, a backfire occurs when unburnt fuel exits the engine and ignites in the exhaust system.

This can produce a loud, gunshot-like sound. Both these scenarios can indicate a malfunctioning coil pack that needs immediate attention.

Cost Of Replacing A Bad Coil Pack

The cost of replacing or repairing a bad coil pack can fluctuate significantly based on the make and model of your vehicle.

On average, the price for a coil pack replacement ranges from $120 to $350, including labor costs.

Cost Of Replacing A Bad Coil Pack

Luxury and high-performance vehicles may demand higher prices due to the complexity of their engine design and the quality of the parts used.

For instance, a BMW or Mercedes may cost upwards of $500 for a coil pack replacement.

Conversely, more common vehicles such as a Honda Civic or Toyota Camry might set you back anywhere between $150 to $250 for the same service.

Vehicle Make/ModelAverage Cost Range for Coil Pack Replacement ($)
Luxury/High-Performance (e.g., BMW, Mercedes)$500 and above
Common Vehicles (e.g., Honda Civic, Toyota Camry)$150 – $250
Average Range (across various makes and models)$120 – $350
Standalone Coil Pack Cost$20 – $100

It’s important to note that these prices are averages and can vary depending on your location and the auto repair shop’s rates.

Furthermore, if you have the skills and tools, purchasing a coil pack and replacing it yourself could reduce costs.

A standalone coil pack can cost between $20 to $100, depending on the vehicle model.

Always remember investing in quality parts and regular maintenance can save you from potential breakdown costs in the long run.


A faulty coil pack can lead to power loss, dirty exhaust fumes, engine overheating, erratic temperature readings, rough idling, and a lit check engine light, among other symptoms.

Call for immediate attention to prevent further damage if you notice any of these symptoms of a bad coil pack.

The cost of replacing a faulty coil pack can differ depending on the make and model of your car.

Nevertheless, promptly addressing this issue is paramount to prevent more costly complications.

Regular vehicle maintenance checks can help identify these issues early, ensuring your vehicle remains in optimal condition and potentially saving you from hefty repair bills.

Terrence Hines

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