12 Key Symptoms Of A Bad Ignition Coil With Replacement Cost

Written By: Terrence Hines
Category: Engine

Symptoms of a bad ignition coil can greatly affect your vehicle’s performance. When an ignition coil fails, it causes issues like misfires, reduced fuel efficiency, and stalling.

Identifying the indications of a faulty ignition coil is imperative to ensure that your vehicle maintains its peak performance and needs fewer replacements.

12 Symptoms Of A Bad Ignition Coil

A malfunctioning ignition coil can result in performance issues for your vehicle, manifesting as frequent stalling and difficulties with starting.

A lackluster performance or decreased power and acceleration can also indicate a faulty ignition coil.

Engine misfiring, characterized by an erratic spark output, can result in an uneven running engine. This, in turn, can cause vibrations or shaking when the engine is idle.

Furthermore, a check engine light might signal an ignition coil issue.

It’s crucial to address these symptoms promptly to avoid further engine damage and ensure the smooth operation of your vehicle.

1. Check Engine light:

One of the most common symptoms of a bad ignition coil is the illumination of the “Check Engine” light on your car’s dashboard.

12 Key Symptoms Of A Bad Ignition Coil With Replacement Cost

This light is linked to the car’s diagnostic system, which monitors the vehicle’s operation.

When the ignition coil starts to fail, your engine might misfire, leading to irregular combustion patterns.

The vehicle’s computer detects this irregularity, triggering the “Check Engine” light. However, it’s important to note that other issues can also activate the light.

To ensure accuracy, have your vehicle inspected by a professional when the light is on.

2. Engine Misfiring Or Reduced Power Output:

In the list of many symptoms of a bad ignition coil, engine misfiring or reduced power output is very common.

Malfunctioning ignition coils can lead to incomplete combustion in the engine cylinders, known as a “misfire,” due to a lack of necessary electrical charge to the spark plugs.

Symptoms of a misfire include intermittent power loss, decreased fuel economy, and rough idling.

In severe cases, the engine may sputter, jerk, or stall, especially during acceleration or under load.

A diagnostic scan tool can help identify if a misfire code is stored in your vehicle’s computer, indicating an issue with the ignition coil.

3. Unusual Smells:

One of the distinct symptoms of a bad ignition coil is the presence of unusual smells, particularly that of burning plastic or rubber.

The ignition coil operates under high-temperature conditions because it converts the low voltage from the battery to high voltage for spark generation.

However, a faulty ignition coil may overheat and cause the insulation materials around it to degrade and burn.

The noticeable smell of burning plastic/rubber from the engine compartment? Act promptly, as it signals a serious issue that could worsen if neglected.

In some cases, the burning smell might be accompanied by visible smoke, underscoring the urgency to stop the vehicle and seek immediate professional assistance.

4. Backfiring:

Backfiring is another notable symptom that could indicate a faulty ignition coil.

Backfiring occurs when unburned fuel exits through the exhaust system instead of being combusted in the engine.

12 Key Symptoms Of A Bad Ignition Coil

Possible cause: Failing ignition coil results in insufficient spark, leading to unburnt fuel passing into the exhaust system.

When the fuel in the exhaust system is ignited, it results in a loud bang or popping sound, commonly known as backfiring.

Regular backfiring can indicate ignition coil issues, leading to reduced engine performance, power loss, and potential exhaust system damage. Don’t ignore it!

5. Poor Fuel Economy:

Poor fuel economy is also among the symptoms of a bad ignition coil.

The ignition coil’s role is to convert the low voltage from the battery into the high voltage necessary to ignite the fuel-air mixture in the engine’s cylinders, facilitating combustion.

A faulty or weak ignition coil may not provide an adequate spark, leading to incomplete combustion of the fuel.

Consequently, the engine must work harder and consume more fuel to deliver the same level of performance, leading to a noticeable decrease in fuel efficiency.

Suppose you observe a sudden increase in your vehicle’s fuel consumption without a corresponding increase in mileage or change in driving conditions.

Possible problem: ignition coil. Immediate attention is required to prevent engine wear & costly repairs in the future.

6. Misfires On Acceleration:

If your car experiences a misfire while accelerating, it could indicate a faulty ignition coil.

The ignition coil is crucial for efficient combustion, providing the spark to ignite the fuel-air mixture in the engine’s cylinders.

When the ignition coil fails, it may not produce a consistent, strong spark, causing misfires during acceleration when more power is needed.

This can result in engine performance issues and a check engine light. Continuous misfires can lead to engine and exhaust damage, with high repair costs.

7. Rough Idling And Stalling Of The Engine When Stopped:

Rough idling and stalling can be indicators of a faulty ignition coil. When the coil is in good condition, it ensures efficient power transfer and smooth engine operation.

However, if the coil fails, it may not generate enough spark for combustion. This can lead to jerky idling and potential stalling when the vehicle is at a stop.

These symptoms are more noticeable when the engine is warm, and the car has been running for a while.

It is important not to ignore these warning signs, as doing so can cause further damage, negatively impacting engine performance and lifespan.

To prevent costly repairs, it is recommended to have your vehicle promptly inspected by a professional.

8. Rattling Noise Coming From The Engine:

A rattling noise from the engine can be among the significant symptoms of a bad ignition coil.

This unsettling noise often results from a variable power output due to a faltering spark from the coil.

 Rattling noise coming from the engine

Consequently, the engine struggles to run smoothly, leading to inconsistent combustion and generating a rattling or knocking sound.

More pronounced at idle or during acceleration, this noise indicates that the engine is laboring harder than usual to perform its function.

Immediate professional attention is advised to correct engine strains that can cause damage to other components, enhancing vehicle performance and longevity.

9. Difficulty Starting The Car:

Difficulty starting the car? It could be a failing ignition coil. This crucial component generates a high-voltage spark to initiate combustion and get your engine running smoothly.

When a coil deteriorates, it fails to generate a sufficient spark, leading to inefficient combustion and difficulty starting the car.

The problem might be more noticeable in cold weather or after the vehicle has been idle for an extended period.

If you notice this symptom, get your vehicle inspected immediately by a professional to prevent complications, maintain performance, and ensure engine longevity.

10. Car Losing Power While Driving:

If your car loses power while driving, it could indicate a failing ignition coil. The ignition coil converts battery power into high-voltage energy to ignite fuel and power the engine.

A failing ignition coil can cause inconsistent sparks, leading to improper combustion and reduced engine performance, especially during acceleration or uphill driving.

This issue may also cause jerking or shuttering as the power fluctuates. Ignoring this symptom can cause further damage, harming the costly catalytic converter.

If your car experiences power loss while driving, it’s recommended to have it checked by an automotive professional for a possible ignition coil issue.

11. Increase In Fuel Consumption:

An increase in fuel consumption could be one of the common symptoms of a bad ignition coil.

Ordinarily, the ignition coil’s role is to generate a high-voltage spark to ignite the fuel-air mixture in the engine, leading to efficient combustion and optimal fuel economy.

However, if the coil is faulty, it may not provide a strong enough spark for efficient combustion.

Engine inefficiency leads to increased fuel consumption and decreased performance, as it has to work harder and burn more fuel to deliver the same power.

If you notice your vehicle is consuming more fuel than usual, it would be wise to inspect it by a professional, as a faulty ignition coil might be the root cause.

12. High Emissions:

A faulty ignition coil often causes high emissions. Its main function is to generate a strong spark for efficient combustion in the engine cylinders, reducing exhaust emissions.

However, a malfunctioning ignition coil may fail to create a powerful spark, resulting in incomplete fuel-air combustion.

High emissions

This incomplete combustion leads to increased unburned fuel emissions. These elevated emissions contribute to environmental pollution and can cause a failed emissions test.

If your vehicle emits noticeably higher emissions, it could indicate an ignition coil issue that a certified automotive technician should promptly inspect.

Cost Of Replacing A Bad Ignition Coil

The cost of replacing a faulty ignition coil can vary considerably depending on the make and model of your vehicle, the specific price of the part, and labor costs.

On average, you can expect to pay anywhere from $200 to $300 for a professional replacement.

This typically includes the cost of the ignition coil, which can range from $50 to $100, and labor fees, which can range from $150 to $200.

However, prices can soar if your vehicle has a complex coil design or multiple coils need replacement.

It’s crucial to remember that delaying replacement could result in further damage to your engine and other parts, potentially leading to more expensive repairs.

Thus, promptly replacing a faulty ignition coil is highly advisable despite the cost.


If you’re experiencing the symptoms of a bad ignition coil, you might notice a check engine light, engine misfires, strange smells, backfires, poor fuel economy, rough idling, stalling, etc.

Also, rattling noises, difficulty starting, power losses, increased fuel consumption, or high emissions can all indicate an impending ignition coil issue.

These symptoms should not be ignored as they could lead to more expensive repairs if left untreated.

Moreover, replacing a bad ignition coil can vary in cost depending on the make and model of your vehicle and the region in which you live.

Replacing an ignition coil usually costs $200 to $300, including parts and labor. Ignoring signs of a faulty coil can cause costly engine damage, requiring expensive repairs.

If you notice any signs, it’s crucial to have your car inspected by a trusted mechanic promptly.

Terrence Hines

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