What Is An Ignition Coil and Why Is It Important?

Have you ever wondered how the fuel is ignited in your engine? The answer is the ignition coils create the high voltage needed by the spark plugs to make a spark. The spark, of course, ignites the fuel mixture.

What is an Ignition Coil and How Does it Work?

Ignition coil

Normally, there’s one ignition coil for each cylinder. It’s a tube-shaped part composed of a laminated iron core wrapped in two coils of copper wire. The coil is either connected directly to the spark plug, or it sits nearby and is connected with a short high voltage wire.

Modern engines no longer have distributors. Instead, the powertrain control module tells each coil when to fire it's spark plug. Here’s how the process works:

  1. Turning the key to the ignition position when you are starting the car energizes the ignition system, including the coils.
  2. The ignition coil transforms the battery’s low voltage into a high voltage current.
  3. The powertrain control module tells each coil and plug when to fire.
  4. The spark plug then ignites the air/fuel mixture, which produces enough combustion to power the engine.

Why Ignition Coils are Important

Car batteries only produce 12 volts, which isn't enough voltage for the spark plugs to make a spark. Spark plugs need anywhere from 12,000 volts to 45,000 volts to work properly. That’s why every car with an internal combustion engine has an ignition coil. 20 or 30 years ago, vehicles only had one coil that fired all of the spark plugs. Modern vehicles use one coil per cylinder. This allows for better fuel economy, reduced emissions, and longer plug life.

What to Expect When One of Your Ignition Coils Fails

Without a functioning ignition coil, one of your spark plugs won’t fire and as a result, your engine will have trouble getting the power it needs. More specifically, you’ll experience some of the following issues:

  • Backfiring
  • Stalling
  • Decreased fuel economy
  • A rough idle
  • A loss in power and acceleration

Neglecting to replace a bad ignition coil can lead to long term damage to the engine and exhaust system. Also, poor fuel economy can easily eat up more money than the repair costs. That’s why it’s important to pay attention to the symptoms of ignition coil failure and replace it as soon as possible.

How to Replace Your Bad Ignition Coil

Sub ignition coil

Image Credit: Smart-Service

Luckily, replacing an ignition coil is something you can easily do at home with a socket, wrench, and flathead screwdriver. First, you’ll need to order a genuine OEM replacement ignition coil. At Subaru Parts Plus, we sell OEM Subaru ignition coils at wholesale prices. To find the right part for your car, look up your model in our catalog, or take a look at this list of our best selling ignition coils:

  • Part No. 22433AA590: For 2009-2011 Forester and Impreza models
  • Part No. 22433AA580: For 2004-2010 Forester, Impreza, Legacy, and Outback models
  • Part No. 22433AA551: For 2004-2005 Impreza models
  • Part No. 22433AA652: For 2013-2014 BRZ and XV Crosstrek models
  • Part No. 22433AA612: For 2011-2018 Legacy, Outback, and Tribeca models

Once you have your replacement part, you can replace the bad ignition coil using this process:

  1. Open your hood.
  2. Remove the plastic cover from the engine (if there’s one).
  3. Disconnect the battery.
  4. Unscrew the screw(s) holding the bad ignition coil in place.
  5. Unplug both ends of the ignition coil and then gently pull it out.
  6. Install the new ignition coil in the reverse order.