Parts for your 2017 Subaru Forester-Ignition coils

2017 Subaru Forester ignition coils — what they do, when to replace, and how to keep them happy

Per Subaru’s factory workshop manual and parts catalogues for MY17 Forester, all petrol engines (FB25 2.5i and FA20F 2.0XT) use four individual coil-on-plug ignition coils. The diesel EE20 Forester doesn’t use ignition coils because it’s a compression-ignition engine, it relies on fuel pressure and compression rather than a spark. If the vehicle is a petrol 2017 Forester, ignition coils are very much relevant.

On the petrol models, each coil sits directly on a spark plug, transforming the 12‑volt battery supply into the high voltage needed to jump the plug gap and ignite the air–fuel mix. This coil-on-plug setup improves spark energy, timing accuracy, and reliability under the bonnet—handy given the heat-cycling these boxers see.

Coils aren’t a scheduled replacement item in Subaru servicing, they’re replaced on condition. Still, they deserve a check at major services. Typical life can exceed 150,000 km, but heat, oil contamination, or moisture can shorten it. Spark plugs should be changed per Subaru’s schedule for the specific engine—fresh plugs reduce coil workload and misfire risk.

• Tell-tales of a dodgy coil: rough idle, hesitation under load, poor fuel economy, harder cold starts, and a flashing or steady Check Engine light. Common OBD-II codes include P0301–P0304 (misfire) and P0351–P0354 (coil primary/secondary).
• Quick diagnosis tip: on a misfiring cylinder, swap the suspect coil to another cylinder. If the misfire moves with it, the coil’s the culprit.
• Care tips: keep the plug tubes dry, replace hardened coil boots, and avoid yanking coils by the connector. Use proper torque on spark plugs so heat transfer is right and the coil boot seals properly. A smear of dielectric grease in the boot helps future removal and resists moisture.

When replacing, use OEM or a reputable equivalent that matches the Subaru spec for dwell and resistance. Fit new boots if they’re perished, and always inspect the connectors for heat damage. After install, clear codes and road test under load to confirm the fix. Done right, fresh plugs and healthy coils restore smooth running, better fuel economy, and crisp throttle response—ideal for long Kiwi and Aussie kilometres.

Popular questions

Do all 2017 Subaru Foresters have ignition coils?
Petrol models (FB25 2.5i and FA20F 2.0XT) have four coil-on-plug units. The EE20 diesel has no ignition coils, as diesels don’t use spark ignition. If unsure, check the compliance plate or engine code.

How often should ignition coils be replaced on a 2017 Forester?
They’re not a routine service item. Replace only when there are symptoms or fault codes, and keep plugs on schedule to protect the coils. Many last well past 150,000 km, but high heat or oil ingress can bring that forward.

Can I drive with a bad ignition coil?
It might run, but it’s not wise. Misfires can damage the catalytic converter and increase fuel use. If the Check Engine light is flashing, park it and sort the issue promptly.