How Do you Know Which Ignition Coil is Bad

How Do you Know Which Ignition Coil is Bad? Definitive Guide for 2024

Internal combustion engines are the most common kind of propulsion for automobiles on the road today. These engines need three things to function properly: fuel, air, and electricity. Because it generates the appropriate amount of electrical current, the ignition coil is an essential component of modern automobiles.

For an engine to function effectively, it is dependent on the ignition coils being in excellent shape and working efficiently. Accordingly, if your engine isn’t running as it normally does, a damaged ignition coil might be to blame. And it’s really important how do you know which ignition coil is bad?

In the event that the ignition coil is damaged in any way, the vehicle will not start. Even worse, it may come to a complete halt altogether. Therefore, it is very important to be aware of the indicators that indicate a failed ignition coil.

What is an ignition Coil?

What is an ignition Coil

A motor’s ignition coils provide a crucial but often overlooked function. Ignition coils are often overlooked, despite their crucial role in supplying electricity to spark plugs, which are mostly responsible for igniting the combustion process.

Spark plugs get an amplified voltage from the coil, which receives its source from a 12-volt battery. It’s just as crucial to recognize the symptoms of a failed ignition coil as it is to know when your spark plugs are dying.

If you believe that your car has defective coils or is suffering any of the following symptoms, you should have a professional technician take a look. You can read about How Do Oil Rigs Move?

Signs of ignition coil fails

Signs of ignition coil fails

The car won’t start

Getting into your automobile, turning the key, and then discovering that the vehicle would not start is one of the most disheartening things that can happen. One of the most frequent reasons a car will not start is because of the ignition coils, but there are numerous other potential causes. If your car has difficulties starting when it is cold outside, the problem may be with the ignition coils. You also check our guide for Why does a piece of spark plug shatter glass?

Your check engine light comes on

There is sufficient reason for the warning light to be illuminated for the engine. Incorrect ignitions and other performance issues may cause the computer to trip, which will cause the check engine light to come on.

Engine stalls

Problems with performance are sometimes an indication of an ignition coil that is not performing properly. If the spark plugs aren’t working properly, the engine can die as you come to a stop, and the automobile might turn off as well.

Decreased fuel economy

It’s possible that the decrease in the gas economy you’ve been seeing is due to a malfunctioning ignition coil. If the battery is unable to provide an adequate amount of power to the spark plugs, your vehicle will have to exert more effort in order to move ahead, which will cause it to use an excessive amount of fuel.

Oil leak

In most cases, the ignition coils will be kept in a container that is filled with oil. If the coil becomes too hot, there is a possibility that oil may leak out of the casing. Because of this, the performance of the vehicle may be negatively impacted if the carburetor is flooded.

Backfiring and poor catalytic converter performance

If your vehicle’s exhaust is filling the cabin with black smoke and reeking of gasoline, it may be an early sign of ignition coil failure. Unburned gasoline is released in a backfire when it is discharged backwards via the engine’s exhaust system. Any unchecked buildup in your exhaust system, especially the catalytic converter, might lead to expensive repairs.

Excessive Smoke

When the ignition voltage is being created by an ignition coil, the ignition spark plugs may emit a significant quantity of smoke. This took place as a direct result of the ignition spark plugs overheating, which led to the oil on the plugs being completely consumed.

How to test ignition coils?

How to test ignition coils

Swapping coils

Whether your automobile has a single coil, a multipack, or a Coil-on-Plug ignition system, swapping out the ignition coil with a known good one is a quick and easy place to start troubleshooting. Misfire on one cylinder is common in such circumstances, as was described above.

Let’s imagine your Coil-on-Plug-equipped car has a misfire in cylinder 3. Take out a different coil, like the one in cylinder 6, and replace it with the one in cylinder 3. If you have a code reader, you may now erase any warnings from your engine. If you did, be sure to remember the engine code. You may also like some of the What to do with a car with a blown engine?

General Inspection

Check every older canister coil carefully for any signs of cracks, burns, melting, or leaks. Canister coils should be replaced if any of these issues are discovered. Careful investigation is required since this is often an indication that there is an issue all by itself.

Test The Windings with A Multimeter

For information on what the appropriate resistance reading for both the main and secondary windings should be, see the repair handbook specifically written for your car or look it up online. Both need to be examined.

To test the primary and secondary windings, connect the positive and negative leads of the multimeter to the appropriate terminals as directed. Depending on the coil’s design, different coils will have various contact points. You should be able to find out precisely where and which pin to touch off to in your repair manual or online.

Check the multimeter reading and compare it to the main and secondary winding resistance parameters.

Spark Test or Active Analysis

Keep in mind that when a coil fails, it usually becomes brittle. It may still generate a spark and may keep the car running at times, but it often misfires when subjected to heavy loads or rapid acceleration. Sometimes the coil just quits operating without any warning.

In order to confirm the issue, it is often necessary to do a spark test or output test on the car itself, rather than just hope that the new components would do the trick. In any Coil-on-Plug (COP) car, the ignition coil change described in step #1 is often the fastest and simplest approach to verify whether or not there is an issue with the coil.

When the coil is installed on the vehicle, a spark test or active investigation of its performance may be conducted using a variety of instruments and techniques. Before doing any of them, make sure you are familiar with spark test techniques, which may be found in a repair manual or online lesson.

Accidental electrocution or significant bodily harm might arise by just taking out coil wires with the engine running. The “power balance test” is another technique you might look at if you’re having trouble pinpointing which cylinder is malfunctioning.


Where is a vehicle’s ignition coil?

Depending on the make and model of your car, the ignition coil or coils may be located in a different part of the engine. There is a separate ignition coil for each spark plug in certain automobiles, and they are all mounted on top of the engine block. In contrast, some engines just need one coil to fire all of the spark plugs. In addition, your car may have many ignition coils in a single assembly.

Why do ignition coils fail?

Although most ignition coils are sturdy and built to endure, they are not invincible. Spark plugs and wires are the most common cause of ignition coil failure. Therefore, your ignition coils are more likely to break before their time if your car has a rich or poor fuel-to-air ratio. Ignition coils are easily broken by excessive heat or vibrations in an engine. However, most cars may go between 80,000 and 100,000 miles before the ignition coil has to be replaced.

How do you replace a damaged ignition coil?

Ignition coils may often be swapped out with little effort due to their simple plug-and-play nature. Even a novice do-it-yourself mechanic should be able to change these coils without any help from a mechanic if they are in your car. However, not all coils are easily accessible.

If you want to take on the project on your own, however, you will simply have to cover the price of the necessary materials. Ignition coil repair costs may be anything from $40 to $300, depending on the car. There may be labor expenses if you hire a mechanic to complete the work. These will likely be affected by the specifics of your engine’s layout and the placement of the faulty ignition coil.

What is your next step?

You need working ignition coils to keep your car operating smoothly. Keeping an eye out for signs of a failing ignition coil is essential. It’s also a good idea to replace your ignition coils as recommended by your car’s maker to keep your automobile running smoothly.

AutoZone is the place to go for any automotive component, whether it be an ignition coil, a tool, or anything else. If you need high-quality auto parts, just go online or to your local AutoZone.


Now we have reached the end of the discussion. I am pretty sure that you don’t face any problems recognizing and identifying the ignition coil and can easily tell which one is bad and which one is good.