Ignition Coils : Problems, Symptoms, and Replacement

Published: 09/14/22 •  9 min read

Modern petrol engines use ignition coils to create high voltage to spark the spark plug.

An ignition coil is an integral part of the vehicle’s ignition system. It converts 12V battery power to high voltage for a spark to be created at a spark plug. The spark ignites the mixture of air and fuel in the engine’s cylinders.

Modern cars only have one ignition coil per piston. The coil is usually installed directly over the spark plug. This arrangement is known as coil/on-plug.

Some cars combine the ignition coils of all cylinders into one coil package. A single ignition coil can be used for all cylinders in older vehicles with a distributor.

What is an ignition coil?

ignition coils

The ignition coil or a spark plug is responsible for starting a car’s engine. It is an integral part of the ignition system.

The car’s battery is low in voltage (12 volts) but requires thousands of volts to start the spark plug.

It is a small transformer that converts 12 volts from the car’s battery to the thousands of volts required. The ignition coil provides the spark needed to ignite the spark and create combustion. Your car won’t start if there is no combustion!

This post will focus on a single ignition coil. However, most engines have at minimum four ignition coils. Sometimes, they are grouped in a coil package. It could cause problems in your car’s ignition coils. Being aware of the signs and symptoms of a defective ignition coil is essential. In this article, we will go over them in detail.

Types Of Ignition Coil

There are three types of ignition coils:

Coil-On-Plug is the most popular system with multiple coils. Each cylinder has one ignition coil, and each coil is connected to the spark plug.

A coil-Near-Plug setup might be used if there is insufficient space for a COP. This could be because the spark plugs protruded from the cylinder head. The coils would then be connected to the plug using short plug wires. Depending on whether your COP or CNP system is used, there are different ways to inspect for ignition coil problems.

Problems With Ignition Coils

Many cars have faulty ignition coils. A failed ignition coil can cause engine shaking, sputtering, and misfiring. You can find the culprit on the engine light. The dashboard will either flash frequently or remain on. A faulty coil can result in the engine not starting for cars with a single ignition coil.

An ignition coil is more susceptible to failure if spark plugs aren’t replaced regularly. The reason is that an older spark plug has a more significant gap between electrodes and higher electrical resistance. This puts strain on the ignition coil.

Symptoms of A Defective Ignition Coil

Let’s now discuss the symptoms of a defective ignition coil.

Poor Fuel Economy

A bad ignition coil could cause less mileage. This happens because your system injects more fuel to compensate for the fact that your spark plugs don’t get enough power

due to a faulty ignition coil. Fuel leaks are also a sign of a bad ignition system. A failing MAF sensor or a dirty engine filter can cause poor fuel economy. These potential problems should be addressed immediately.

Difficulty While Starting the Engine

Your ignition coil could be causing difficulty in starting your car’s engine. Some engines are equipped with multiple ignition coils. If you have multiple lousy ignition coils, you could experience trouble starting your engine. Many other problems could make an engine difficult to start. However, having difficulty starting your engine is insufficient to prove an ignition coil problem.

Check Engine Light

The engine light will indicate that something is wrong. The engine light will turn on if there is an ignition coil problem, which should not be ignored. However, as with other symptoms, engine lights can also be caused by engine problems.

An OBD-II (on-board diagnosis) check is the best way to determine why your engine light is on. A mechanic can do an OBD-II scan, or you may do it yourself using an OBD-II scanner. Codes P0300 through P0312 are misfire codes, while codes P0350 through P0362 indicate ignition coil problems.

Engine Misfiring

If your engine stalls, misfires, or stops when idle, or when you suddenly stop or accelerate suddenly, it could indicate a problem in the ignition coil. If the engine makes a misfire, it could sound like a wheezing or sputtering sound or feel like you are vibrating or jerking. This is a sign that the engine’s cylinders are not firing properly.

Engine strain can increase the likelihood of misfires and cause emissions. A bad ignition coil can cause increased exhaust emissions and a stronger gas smell. Many other factors could cause misfires, like difficulty starting your car’s engine. Faulty ignition coils can cause a car to stall due to irregular sparks from the spark plug.

Diagnose a Failing Ignition Coil

If done incorrectly, testing an ignition coil could prove dangerous. We recommend seeking the guidance of a qualified specialist if you are unsure how to test an ignition wire safely.

Depending on the type of your ignition coil and your level of expertise, there are many other tests that you can perform.

As discussed above, you can test for ignition coil problems using an OBD-II scan. This will require an OBD-II scanner. Codes P0300 through P0312 are indicative of engine misfires. Codes P0350 through P0362 indicate ignition coil problems.

You will need to look at the ignition coil for other test types. You will need to look at your vehicle’s manual to determine the location of your ignition coil. It would be best to take all precautions to ensure you don’t get electrocuted.

Once you have located your ignition coil, it is time to inspect for signs of damage. You can check the ignition coil wiring for damage or deterioration. Also, examine the connector and coil harness for any faults. If the problem persists, remove each ignition coil from your engine and inspect it for damage. It would be best if you carefully look for moisture signs in the ignition coils. Liquids can cause damage.

You can also run another test if you have a CNP ignition. For this type of test, you should always use insulated tools.

  1. Turn off the engine of your car.
  2. Take out the spark plug wire.
  3. Connect a new sparkplug to the sparkplug wire.
  4. Use insulated tools to hold the threaded end of the spark plug to a metal part of your engine.
  5. Use the appropriate tools to remove the fuse from your fuel pump.
  6. Turn on the car engine.

After the engine has started, look for sparks in the spark plug gap. Your ignition coil should produce blue sparks if you see them. If you don’t see any blue or orange sparks, your ignition coil is likely not working correctly. Once done, return the parts to their original positions.

Safety Precautions For Ignition Components

The ignition coil can produce extremely high voltages that could harm your health. Follow the safety precautions in your vehicle’s service manual when working with ignition components. Disconnect the negative battery cable first before inspecting or replacing an ignition coil.

Driving With a Defective Ignition Coil

An engine that has a bad ignition coil can often misfire. Driving with such a defective engine in certain cars can lead to the catalytic conversation overheating and melting. It is costly to replace the catalytic converter. There have been cases where a shorted ignition wire caused a damaged engine computer (PCM). Some car manufacturers advise against driving if your engine is not firing correctly. We recommend having your vehicle checked as soon as possible. For more information, consult the owner’s manual.

Replacing the Ignition Coil

An ignition coil inspection usually involves measuring the resistance between particular ignition coil terminals. The ignition coil should be replaced if the resistance exceeds specifications.

To identify a bad ignition coil, mechanics may swap it with a good coil from another cylinder to check if the misfiring continues to the same cylinder or moves with the coil. A mechanic might change the ignition coils in cylinder 2 or 3 if the code is P0302 (cylinder 2-misfire). The engine may then be run for a brief time. The trouble code P0302 changes to P0303 (cylinder two misfires), and the ignition coil located initially at cylinder number 2 becomes bad.

It is also advised to replace ignition coils if they are damaged by arcing, cracks, or any other damage that could cause them to fail.

A defective ignition coil cannot be repaired. It must be replaced. It is easy to replace an ignition coil in cars with a 4-cylinder engine or an inline-6 engine. The cost for replacing one coil is between 180-$380.

An intake manifold is required to access rear ignition coils in some V6 engines. This requires more labor and is more expensive ($280-$500 per rear coil). Your mechanic might recommend that you replace all three rear coils in such cases.

If one of your ignition coils fails, you should replace all spark plugs. The ignition coils will last longer if equipped with new spark plugs.

Replacement Costs for Ignition Coils

You can order a replacement ignition coil online on Amazon if you have discovered an issue with your ignition coil. Prices of ignition coil will vary depending on your car’s make and year, but older models will be around the PS50 mark. The cost for replacing one coil is between 180-$380.


An ignition coil problem does not pose a safety risk and is relatively inexpensive to fix. Even though the ignition coil may be defective, you can still drive it if necessary. However, you will notice a decrease in car performance. If left untreated, an ignition coil issue can cause damage to other parts of your car, including the catalytic converter. This could lead to more severe problems.