Parts for your 2018 Subaru Forester-Ignition coils

2018 Subaru Forester ignition coils: what they do and how to look after them

Per Subaru’s Factory Service Manual (STIS) and OEM parts catalogues for the 2018 Forester (FB25 2.5‑litre and FA20F 2.0‑litre turbo), this model runs a direct coil‑on‑plug ignition system — one ignition coil per cylinder. So yes, ignition coils are absolutely fitted and relevant on the 2018 Subaru Forester.

Ignition coils take the 12‑volt supply from the battery and step it up to tens of thousands of volts, delivering a crisp spark straight at the plug. On the Forester’s boxer engine, each coil sits right on top of its spark plug under the rocker covers, with the ECU firing them precisely to light off the air‑fuel mix. Coil‑on‑plug design cuts energy losses, helps cold starts, trims emissions, and keeps the engine running smooth as.

There’s no fixed replacement interval for coils on this model — they’re a service‑on‑condition item. During regular servicing, it’s smart to inspect coil connectors and boots for heat hardening, oil intrusion from rocker cover leaks, cracked housings, or green/white corrosion on terminals. When spark plugs are due (typically around 100,000 km for the FB25 with iridium plugs, often shorter on turbo FA20F — check the owner’s handbook), it’s the perfect time to assess the coils because they’re already accessible.

Common signs a Forester coil is on the way out include:

• Rough idle, hesitation, or a stumble under load
• Poor fuel economy and a whiff of raw petrol
• Check Engine Light with misfire codes (P0300–P0304)

Diagnosis is best done with a scan tool, a misfire counter, and by swapping coils cylinder‑to‑cylinder to see if the misfire follows. On replacement, use quality OEM‑equivalent coils, lightly apply dielectric grease inside the boots, ensure the connector latches positively, and torque the hold‑down bolt to manufacturer spec (around 8–10 N·m is typical). Avoid yanking on the connector wires and keep water and engine‑bay cleaner away from the coil tops.

If one coil fails at high kilometres, replacing the single faulty unit is fine, but many techs recommend changing the full set on turbo models or where heat cycling has clearly cooked the lot. Keeping on top of rocker cover gasket leaks and renewing plugs on time will help the coils live a long, drama‑free life.

Popular questions about 2018 Subaru Forester ignition coils

How often should the ignition coils be replaced?
There’s no scheduled interval. Coils are replaced when they show faults or physical damage. Inspect them at each plug change and major service, and test if there are misfire symptoms or codes.

Can a bad ignition coil damage the catalytic converter?
Yes. A weak or dead coil causes misfires that let unburnt fuel hit the cat, overheating and potentially melting the substrate. Driving long with a misfire can get expensive, so sort coils promptly.

Are coils the same between the 2.5‑litre and 2.0‑litre turbo?
Not necessarily. The FB25 and FA20F can use different coil part numbers and calibration requirements. Always match by VIN/engine code or OEM part lookup before ordering.