How To Diagnose Subaru Ignition Coil Problems

To avoid long-term damage to the engine and exhaust system, you have to replace a bad ignition coil as soon as possible. With a bad ignition coil, your engine won’t make the power it should, and your car's performance suffers as a result.

Symptoms Of A Bad Ignition Coil

Are you starting to see the symptoms of a bad ignition coil? It’s worth setting aside about 10 minutes to diagnose the issue so you can take care of the problem as soon as possible. The most common symptoms of a failed ignition coil similar to the symptoms of a bad spark plug. It’s because the bad ignition coil can’t fire the spark plug it’s connected to. Keep an eye out for the following warning signs:

  • Rough idling
  • Backfiring
  • Stalling
  • Increased fuel consumption
  • Reduced power and acceleration

The Diagnostic Process

Bad Subaru Igniton coil

The Subaru ignition coil test is actually a simple and straightforward process. The following set of instructions is specifically for the Subaru Forester. The process is similar for most Subaru's, but you should google to verify the resistance specifications.

While testing your ignition coils, it’s a good idea to inspect the spark plugs and wires, too. The only tool you’ll need is a digital multimeter to measure resistance.

  1. Open your hood and unplug all four wire pin connectors on the coil pack.
  2. Plug the multimeter leads into the left two outlets on the face of the coil pack. The resistance reading should be about 0.73 ohms, plus or minus 10%.
  3. Repeat with the right two outlets on the coil pack.
  4. If either reading is well below or above 0.73, then there’s an issue with the ignition coil pack and it needs to be replaced.

If the coil pack looks good, then it’s time to test the secondary resistance at the spark plug wire terminals. To do this:

Find the spark plug wire terminals and then plug your multimeter in two of them. Make sure that both terminals are pointing directly opposite of each other. The reading should be about 12,800 ohms, plus or minus 15%. If the reading is off, then the coil pack is bad and it needs to be replaced.

Ordering An OEM Replacement Ignition Coil Pack

New Subaru ignition coil

If you have a socket, wrench, and flathead screwdriver, you can replace your ignition coil pack right at home in a matter of 10-20 minutes. Before starting the project, you need to order a replacement ignition coil pack. We recommend OEM over aftermarket for a number of reasons, including precise fitment and reliability.

At Subaru Parts Plus, you can find OEM ignition coils at wholesale prices. Visit our catalog to find the right ignition coil for your Subaru model, or check out 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