Bad Ignition Coil Symptoms

Bad Ignition Coil Symptoms

An ignition coil transforms the low voltage from the battery into the high voltage necessary to ignite the spark plugs. When the ignition coil malfunctions, it can cause many problems for the vehicle.

Understanding bad ignition coil symptoms is crucial to ensure proper maintenance and avoid potentially hazardous situations.

These symptoms may include erratic engine performance, stalling, difficulty starting the engine, decreased fuel efficiency, and even engine misfires. 

The consequences of a malfunctioning ignition coil may lead to further damage to other engine components, ultimately resulting in costly repairs.

Therefore, it is essential to recognize the signs of a bad ignition coil to promptly address the issue and maintain the vehicle's optimal performance.

What Is an Ignition Coil?

An ignition coil is crucial in generating the electric pulses needed for a functional engine. Acting as an electrical transformer, it transforms the battery's power into the high voltage required to burn fuel and air mix in the engine.

The transformer comprises two coils, the primary and the secondary, wrapped over a magnetic core. The electrical current running through the primary coil produces a magnetic field encircling the core.

The magnetic field's abrupt collapse precedes high voltage generation in the secondary coil. This occurs due to the break in the current flow brought on by the disconnection of the primary coil. The combustion process then starts due to the movement of the said high voltage through the distribution caps to the spark plugs.

The numerous advantages and characteristics of distinct ignition coils, such as canister-style, coil-on-plug, and coil-near-plug designs, make them fundamental components for the proper operation of an automobile engine.

Malfunctioning of the ignition coils can cause numerous issues, including weak acceleration, stalling, and reduced gas mileage.

What Are the Causes of a Bad Ignition Coil?

Identifying the root causes of ignition coil failure is essential for correct upkeep.

Multiple variables can lead to an ignition coil's malfunction, and recognizing these causes is imperative for effective maintenance.

1. Heat

Heat can be a causative force of a faltering ignition coil. The insulation inside the coil may be detrimentally affected over time if temperatures outstrip a certain threshold, resulting in short-circuiting or total breakdown.

This issue can worsen by other factors, such as improper spark plug gaps, which can cause the ignition coil to work harder than necessary, resulting in increased heat and potential damage.

2. Electrical Issues

Another common cause of ignition coil failure is electrical issues. Electrical disturbances such as voltage surges and short circuits can lead to dysfunction or early coil breakdown.

Malfunctioning could result from faulty wiring, frayed connectors, or any other electrical issue relating to the car's ignition system.

3. Wear and Age

Age and wear are also significant contributors to ignition coil failure. Over time, the coil's internal components can wear out, leading to a performance loss or complete failure.

Other factors contributing to wear include exposure to harsh chemicals or environmental conditions, such as salt or moisture.

4. Improper Installation

Lastly, improper installation or handling of the ignition coil can cause damage or failure.

This can include incorrect wiring, over-tightening of mounting bolts, or physical damage to the coil itself.

Bad Ignition Coil Symptoms

Recognizing the symptoms of a bad ignition coil is essential for identifying potential issues and taking appropriate action to prevent more severe problems.

1. Engine Misfires

One of the most common symptoms of a bad ignition coil is engine misfires. Misfires occur when the spark plug fails to ignite the fuel-air mixture in the combustion chamber.

This issue can cause the vehicle to run rough, with noticeable vibrations and decreased power and acceleration.

2. Stalling

Stalling is another symptom of a bad ignition coil, particularly when the engine is idling.

The lack of sufficient spark can cause the engine to shut down or stall entirely, making it difficult or impossible to restart.

3. Difficulty in Starting the Engine

Difficulty starting the engine is another symptom of a bad ignition coil. A weak spark can prevent the engine from starting or cause it to start intermittently.

The engine may also take longer than usual to start, requiring several attempts before it runs correctly.

4. Low Fuel Efficiency

Decreased fuel efficiency is also a common symptom of a bad ignition coil.

The engine's reduced performance could force it to expend more energy than necessary, leading to elevated fuel consumption and diminished gas mileage.

5. Other Symptoms

Other symptoms of a bad ignition coil include illuminated check engine light, rough idling, and a noticeable decrease in engine power.

A skilled mechanic should inspect the automobile to pinpoint the exact origin of the difficulty.

How To Diagnose a Bad Ignition Coil

Diagnosing a bad ignition coil is essential to identify the root cause of vehicle issues such as engine misfires, stalling, difficulty starting, and decreased fuel efficiency.

The proper diagnosis requires a thorough understanding of the ignition system's function and the use of specialized tools and equipment.

Below are the steps to diagnose a bad ignition coil:

Step 1

A visual inspection is usually the first step in diagnosing a bad ignition coil. Look for signs of physical damage, such as cracks or burn marks on the coil or surrounding wiring.

Inspect the spark plugs for wear or damage, and check the wiring and connectors for proper installation and damage.

Step 2

The next step is to use a scan tool to read any diagnostic trouble codes (DTCs) stored in the vehicle's computer.

DTCs can provide valuable information about potential issues with the ignition system, such as misfires or ignition-related problems.

Step 3

After conducting a visual inspection and checking for DTCs, the next step is to conduct a spark test. A spark tester can check for a spark at the spark plug.

The ignition system could exhibit a scarcity or lack of spark or a weak spark which may imply an issue with the ignition coil or attendant components.

Step 4

If the spark analysis presents a difficulty with the ignition coil, you can use a digital multimeter to test the resistance of the ignition coil.

The readings should fall within the manufacturer's specifications. If the resistance is outside the specified range, it may indicate a problem with the ignition coil.

Step 5

If all the above tests indicate a problem with the ignition coil, the final step is to conduct a coil output test.

Use a coil output tester to verify that the coil produces the correct voltage and current output. If the output test indicates a problem, then replace the ignition coil.

How To Fix or Replace a Bad Ignition Coil

To fix a bad ignition coil is to confirm the coil is the problem. This is typically done through a thorough ignition system diagnosis, including visual inspection, DTC reading, spark testing, resistance testing, and coil output testing, as discussed in the previous section.

Step 1: Remove the Bad Coil.

The first step is to remove the faulty coil to address an identified ignition coil issue. To know its position consult the car's manual or repair manual.

Step 2: Replace the Coil.

Upon removing the faulty coil, replace it with a newly acquired one of the correct type and specification for the specific vehicle make and model.

Adhere to manufacturer instructions when installing, properly connecting, and affixing all associated wiring and connectors to their predetermined values.

Step 3: Test the Vehicle.

After installing the new ignition coil, test the vehicle's operation to confirm the issue has been resolved.

Confirm that the motor runs without difficulty and there are no visible signs of faltering, idling, or fuel use problems by going on a trial run.

A specialist technician can provide instructions on the needed repairs and replacements to certify the car's ignition system is functioning correctly.

It might necessitate more than only a substitution of the problematic ignition coil. Other parts of the ignition system, such as the spark plugs, spark plug cables, or the ignition control unit, may also necessitate switching out.

How To Prevent Ignition Coil Issues

Here’s how to prevent ignition coil issues.

1. Maintenance.

Regular maintenance is essential for preventing ignition coil issues. Routine care includes scheduled oil changes, air filter replacements, and tune-ups.

Regular maintenance helps keep the engine running smoothly, reducing the likelihood of stress on the ignition coil.

2. Stay Clear of Rough Driving.

Avoid harsh driving conditions that can put additional stress on the ignition coil.

For example, avoid driving in heavy traffic or stop-and-go traffic, which can lead to overheating of the ignition coil.

Additionally, avoid harsh driving habits, such as rapid acceleration and hard braking, which can put extra stress on the ignition coil.

3. Maintain Accurate Fuel Levels.

Maintain the correct fuel and oil levels to ensure proper engine operation.

Low fuel levels and dirty oil can cause additional stress on the ignition coil, leading to premature failure.

4. Use Quality Coils.

Use high-quality ignition coils when replacing the old ones. High-quality ignition coils are more durable and have better heat dissipation characteristics, reducing the likelihood of stress on the ignition coil.

5. Routinely Check the Ignition Components.

Regularly check and replace the spark plugs, wires, and other ignition system components to ensure optimal operation.

Worn spark plugs and wires can cause additional stress on the ignition coil, leading to premature failure.

6. Don’t Mess With the Electrical System.

Finally, avoid tampering with the vehicle's electrical system or installing non-standard components that cause electrical interference or voltage fluctuations.

Electrical interference can damage the ignition coil and other parts, leading to costly repairs.


By knowing the bad ignition coil symptoms, you can prevent more costly ignition coil issues by quickly dealing with minor issues when they occur.

Preventing ignition coil issues requires regular maintenance, avoiding harsh driving conditions, maintaining correct fuel and oil levels, using high-quality ignition coils, and regularly checking and replacing other ignition system components.

Proper maintenance and attention to potential issues can prolong the life of the ignition coil and ensure the best operation of the vehicle's ignition system.