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. They ultimately allow spark to be created and the vehicle to start and run.
Do different cars have different types?
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.
Why do they fail?
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.
How will I know if an ignition coil needs to be replaced?
The most common symptom of a faulty ignition coil is 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 and are often accompanied by a check engine light. In some cases, a faulty ignition coil can even prevent a vehicle from starting. A diagnostic test by a technician can determine if your ignition coils are the cause of your engine running poorly.
What if I don’t replace it?
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.
What does it cost, and why?
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 should replace at the same time?
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. 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.
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.