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Blog Car Care Advice How To Care For Your Car: Ignition Coil

How To Care For Your Car: Ignition Coil

January 2, 2020

There are numerous  parts that power a vehicle’s engine and keep it running smoothly.

Most vehicles are designed with internal-combustion engines. These engines need three different components to run: fuel, air, and electricity. If one or more of these components is missing, the engine cannot function. 

Ignition coils are partly responsible for supplying the electrical component of this equation. If the ignition coils are not in good condition, the vehicle’s engine performance could suffer as a result.

But what is an ignition coil? How will you know when to replace an ignition coil? Should you change ignition coils with spark plugs? Keep reading to learn the answers to these questions and more.

What are ignition coils?

Ignition coils are the electrical components on the engine that amplify voltage from the vehicle’s charging system (battery and alternator) and deliver power to the spark plugs. Every spark plug has its own ignition coil.

Ignition coils are necessary because a vehicle’s battery produces a low voltage current that is not strong enough to ignite the fuel and start the engine on its own. To solve this problem, the ignition coils convert the low voltage current from the battery into a much higher voltage current.
To put it simply, ignition coils ultimately allow spark to be created and the vehicle to start and run.


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Do different cars have different types of ignition coils?

The most common type in modern vehicles is coil-on-plug (shown below), which features one ignition coil directly connected to each spark plug. 

Some vehicles feature a central coil pack or individual coils with wires leading to the spark plugs. A smaller number of vehicles employ one coil per two spark plugs, or two ignition cassettes with each powering half of the spark plugs.

Common causes of ignition coil problems

Ignition coils can fail for a variety of reasons. They are not considered wear items, but often, age/use is the cause — thousands of miles of vibrations and high temperatures can lead to failure of the internal parts. 

Moisture damage is also very common — usually from leaking engine oil, but also from other fluid leaks or condensation. 

Lastly, spark plugs that are excessively worn can put extra stress on the ignition coils and lead to premature failure. This is because as spark plugs wear out, the spark plug gap widens. This means the ignition coil will need to provide a higher voltage to overcome this gap. Having to repeatedly produce a higher voltage can put a strain on the ignition coil and cause it to fail prematurely.

How will I know if an ignition coil needs to be replaced?

It’s important to know when to replace an ignition coil, so you can keep your engine running smoothly.

The most common symptom of a faulty ignition coil is engine misfiring, which is when one or more cylinders in the engine is not firing properly due to a lack of air, fuel, or in this case, spark. Misfires generally present themselves as a rough idle or lack of power.

In some cases, a faulty ignition coil can even prevent a vehicle from starting. However, your vehicle could fail to start for a number of other reasons, including a dead battery or faulty starter. A diagnostic test by a technician can determine if your ignition coils are the cause of your engine running poorly.

Your check engine light may turn on if it’s time to replace your ignition coils. But this light could turn on for many other reasons, and a mechanic can inspect your vehicle to determine the problem.

If your vehicle is consuming more fuel than usual, this could also indicate that it’s time to replace your ignition coils. This is because if the spark plugs aren’t receiving enough power due to failing ignition coils, your vehicle will compensate for the decrease in power by increasing its fuel consumption.

Backfiring can also be a sign of an ignition coil problem. A backfire is characterized by a loud banging sound. You may also see black smoke coming out of your exhaust pipe. This is not normal and could indicate that your ignition coils are failing.  

Keep an eye out for these signs of a failing ignition coil. Being aware of these signs will make it easier to determine when to replace coil packs or ignition coils.

What if I don’t replace an ignition coil?

Knowing when to replace an ignition coil is the first step. The second step is actually contacting a mechanic to get it replaced.

A vehicle with one or more faulty ignition coils will lack power and run poorly, or sometimes not run at all. 

Additionally, running a misfiring engine for extended periods can damage the catalytic converters and oxygen sensors due to unspent fuel making its way into the exhaust system.

The bottom line is you should not drive your vehicle if you believe your ignition coils need to be replaced. If you continue to drive a vehicle with failing ignition coils, you could seriously damage the engine.

Should I replace ignition coils with spark plugs?

Ignition coils and spark plugs work closely together. If either one fails, the other cannot function properly. So, should you replace coil packs with spark plugs? It depends.

The most common component to replace in conjunction with the ignition coils are the spark plugs. Worn spark plugs can cause unnecessary load on the coils and there is often some overlap in the labor required to replace both components. If your ignition coils failed as a result of worn-out spark plugs, it is wise to replace both components at the same time.

But if you are simply replacing your spark plugs as part of routine maintenance service, it is not necessary to replace your ignition coils at the same time unless there are signs that they are failing.

In systems with ignition/spark plug wires, it is recommended to replace the wires if they appear old, worn, or damaged. If the ignition coils are damaged by moisture (such as an oil leak), the source of the moisture should be addressed at the same time to prevent the issue from returning prematurely.

If you are experiencing ignition coil issues, contact a mechanic right away. One of the first questions you should ask your mechanic is “Should I replace ignition coils with spark plugs?” Let your mechanic inspect your vehicle to determine if it is necessary to replace both your ignition coils and spark plugs.

How will a mechanic determine when to replace an ignition coil?

A mechanic will need to check an ignition coil’s primary and secondary ignition circuits to determine if the coil needs to be replaced. Mechanics can check both of these ignition circuits with a digital multimeter device. 

A digital multimeter device measures resistance. Your mechanic may need to look in your owner’s manual to find the normal resistance range of your ignition coils. If the primary or secondary resistance falls outside of this normal range, this indicates that the coil needs to be replaced.

Diagnosing and replacing failed ignition coils requires the use of special tools and equipment. Making even a minor mistake could seriously damage the spark plugs or other components of the engine. For this reason, it is best to hire a mechanic to handle this task instead of trying to complete it on your own.

How much does it cost to replace ignition coils?

A simple coil-on-plug can cost anywhere from a couple hundred dollars, where a cassette-style system can be upwards of $1000. The cost is dependent upon the style of coil as well as the difficulty of access.

Is there anything I can do to lower the cost of repair?

By replacing spark plugs at manufacturer-specified intervals and addressing oil leaks when they are minor, excess wear and damage to the ignition coils may be prevented.

Unfortunately, ignition coil failure may ultimately be inevitable due to age, even if the vehicle is well-maintained. In this situation, aftermarket ignition coils are usually available and are a less expensive option, but in some cases they can be less reliable than the original equipment that came on the vehicle.