Blog Car Care Advice 6 Bad Ignition Coil Symptoms (+Causes, Diagnosis, and FAQs)
Car Care Advice

6 Bad Ignition Coil Symptoms (+Causes, Diagnosis, and FAQs)

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Ignition coils are like mini transformers in your vehicle’s ignition system. 

They convert the low voltage from a car battery into a much higher voltage that helps ignite the fuel and start the engine. 

And like any other electrical part, they can go bad too. 
But how do you identify a bad ignition coil?

This article will cover common bad ignition coil symptoms and causes of ignition coil failure. You’ll also find out how to diagnose a faulty ignition coil and the precautions you can take to prevent them from going bad.

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Let’s get started.

6 Symptoms of a Bad Ignition Coil

Each spark plug in your vehicle requires high voltage from the ignition coil (around 15,000-20,000 volts) to generate an electric spark for fuel combustion. Such high demand can damage your ignition coils sooner than you expect.

So you know what to look out for, here are six common bad ignition coil symptoms:

1. Loss of Power

One of the first symptoms you might notice in the case of a defective ignition coil is loss of power. This occurs when irregular sparks fail to bring about the required combustion and gives rise to performance issues, such as making the vehicle feel sluggish.

2. Poor Acceleration and Jerking 

If you have a failed ignition coil, your engine will hesitate to accelerate, taking longer to reach the desired speed. 

Your vehicle may also experience jerking because unused fuel can ignite in the exhaust system, causing loud backfires. Jerks can also occur when you step on the accelerator to increase speed.

3. Engine Misfire 

Irregular sparks can cause a combustion cylinder to fire incorrectly, resulting in engine misfire. 

A failing ignition coil could be the culprit if you experience a misfire when you try to accelerate, idle, or stop your vehicle abruptly. 

Why are misfires a concern?
Frequent misfires can damage the vehicle’s catalytic converter, affecting your engine’s health. Your fuel economy will take a hit, too. 

When misfires happen, the Check Engine Light on your dashboard might pop on to alert you about any problem associated with your ignition system, so make sure not to ignore it.

4. Backfiring 

An engine backfire could point to ignition coil failure in the early stages. A backfire occurs when unused fuel moves out of the combustion chamber and ignites in the exhaust pipes due to heat and pressure.

When the engine backfires, it creates a loud bang, followed by black smoke emerging from the exhaust pipe and a strong gas odor.

Like a misfire, frequent backfiring due to a bad coil can harm your engine components and affect fuel economy.

5. Hard Start and Vehicle Stalling

A faulty coil or ignition coil malfunction can cause the engine to take longer to turn over and start. This happens because the spark plug doesn’t get the proper voltage to create an electric spark, leading to that hard start. 

You may also experience engine stalling. A faulty ignition coil can cause your vehicle to shut down when brought to a stop, and you’ll have trouble restarting it.

6. Illuminated Check Engine Light

The Check Engine Light feature is available in every modern car to alert you whenever something goes wrong in your vehicle. 

Your Check Engine Light can indicate an engine performance issue or problems in transmission, air/fuel delivery, ignition system, etc. 

When ignition coils malfunction or fail, your vehicle’s Engine Control Unit will register the diagnostic trouble codes (DTC) specific to the ignition coil malfunction and activate the Check Engine Light.

DTC codes P0350, P0351, and P0353 up to P0359 are all related to ignition coil malfunctions and can be detected using an OBD-II scanner.

Now that you know the symptoms of a bad coil, let’s look at some causes of ignition coil failure.

4 Causes of Ignition Coil Failure

Ignition coils usually last long but can fail prematurely for various reasons, such as a bad spark plug, heat, faulty coil wiring, fuel leaks, etc.   

Here are the main causes of ignition coil failure:

1. Exposure to High Temperatures

When the ignition coil gets overheated, its ability to conduct electricity is hampered. Exposure to multiple heat cycles and high temperatures can cause the ignition coil to deteriorate faster than usual.

An overheated ignition coil can cause complete failure of the vehicle’s ignition system.

2. Damaged Spark Plug

Worn spark plugs can put more load on the ignition coil, forcing them to overcompensate and operate at a higher voltage.

The voltage overload can overheat the ignition coils and cause them to fail.

3. Engine Vibrations

Excessive vibrations can occur due to an engine misfire or problems associated with the spark plugs. Either way, it can significantly damage the ignition coil windings (primary coil and secondary coil) and their surrounding insulation.

It can also cause shorts or breaks in the secondary coil windings, leading to ignition coil malfunction. 

4. Moisture 

Moisture can damage the seal between the valve cover and the ignition coils.

Once the moisture spreads around the spark plugs and ignition coil, it can cause unwanted oxidation and corrosion, leading to a bad coil pack or complete ignition coil failure.

Want to diagnose your ignition coils? 
Let’s see how you can do that.

How to Diagnose a Bad Ignition Coil?

If you’re unsure about the car parts, it’s best to leave the job to a mechanic. Some ignition coil setups are more complicated to diagnose than a single ignition coil or coil-on-plug setup, so you should let a mechanic handle them.

That said, here’s how to do the swap test to identify a bad ignition coil on an engine with coil-on-plugs:

  1. Plug in an OBD-II scanner in your vehicle’s OBD2 port.
  1. Confirm that the error code is related to the ignition coil. If yes, turn off your vehicle’s ignition switch and allow your engine to cool down. 
  1. Carefully remove the ignition coil from the cylinder displayed in the error code and swap it with a coil from any other cylinder.
  1. Start the engine and pay attention to the error codes.
  1. If the code displays an error, indicating a misfire in the new cylinder and no misfire in the previous cylinder, the ignition coil is faulty and requires replacement.

But is there a way to protect your ignition coil from damage?

What Precautions Can I Take to Prevent Ignition Coils From Going Bad?

While the wear and tear of ignition coils and spark plugs are inevitable, there are some precautions you can take to delay the damage:

Now it’s time to go through some commonly asked questions about ignition coils.

3 FAQs on Ignition Coils 

Here are the answers to some important bad ignition coil questions:

1. How Can I Replace a Failed Ignition Coil?

Some ignition coils come in a plug-and-play design. These faulty coils are easy to replace on your own without any help. 

But there are other types, such as the conventional or electronic ignition coil. These can be tricky to replace if you’re unfamiliar with car parts. In either case, it’s recommended that you contact a professional for ignition coil replacement. 

2. How Often Do I Have to Replace Ignition Coils?

Ignition coils are designed to last for 100,000 miles. But factors like high voltage due to a bad spark plug, heat, and moisture can damage the coil pack early on and cause issues like poor fuel economy and misfires. 

In that case, you should get the bad coil pack replaced sooner.

3. Can I Drive a Car With a Bad Ignition Coil?

While you can push your vehicle to drive a few extra miles with a faulty ignition coil, it isn’t recommended. Avoiding an ignition coil problem may lead to catalytic converter damage, which can be quite expensive to replace.

On the other hand, ignition coil replacement is easy and inexpensive, so there’s no reason to delay the repair.

Final Thoughts 

If you observe performance issues, such as a hard start, irregular sparks, engine stalling, or your Check Engine Light turns on, it could be a sign of a failing ignition coil. Problems stemming from the ignition coil can even affect your expensive catalytic converter.

As such, you should get your ignition system checked and the coil pack replaced.

Why not let an expert like AutoNation Mobile Service fix the ignition coil problem for you? 

AutoNation Mobile Service is a convenient mobile car repair and maintenance solution that offers you the following:

Contact AutoNation Mobile Service for a quick ignition coil replacement or any other car services, and we’ll bring the repair shop to you.