Parts for your 2012 Subaru Forester-Ignition coils

2012 Subaru Forester ignition coils — what they do and how to look after them

Per the 2012 Subaru Forester Factory Service Manual for both the FB25 2.5i and EJ255 2.5XT engines, this model uses direct coil‑on‑plug ignition coils, one per cylinder. Subaru’s electronic parts catalogue, along with NGK and Denso application catalogues, also list four individual ignition coils for the 2012 Forester. So ignition coils are absolutely fitted and relevant on this vehicle.

Each coil’s job is to step the car’s 12 volts up to tens of thousands of volts, creating a strong spark at the plug to ignite the air–fuel mix. Being coil‑on‑plug means there are no long high‑tension leads, the coils sit right on the spark plugs for cleaner firing, better timing control and improved reliability.

Coils are largely maintenance‑free, but they do live in a hot, vibrating spot under the bonnet. Over time the internal windings or the rubber boots can break down, especially if oil or moisture sneaks in. Typical giveaway signs include:

• Rough idle, hesitation or flat spots under load
• Higher fuel use and a sulphur smell from the exhaust
• Check engine light with misfire codes (P0301–P0304) or coil circuit codes (P0351–P0354)

Best practice during regular servicing is simple: keep the coil tops and connectors clean and dry, and inspect them whenever the spark plugs are changed (the Forester’s iridium plugs are commonly due around the 100,000 km mark — check the service book for the exact interval). If there’s oil in the plug tubes, fix the tube seals before refitting coils.

When a misfire pops up, a quick “swap test” often helps: move the suspect coil to another cylinder and see if the fault follows. If it does, that coil is due. There’s no routine need to replace all four at once, but many owners opt to replace the matching rubber boots together if they’re hardened or cracked.

DIY replacement is straightforward for most home mechanics: disconnect the battery, remove the engine cover if fitted, unplug the coil connector, undo the retaining bolt, then twist and lift the coil straight off the plug. Refit in reverse, using a light smear of dielectric grease inside the boot, and always follow the factory torque specs for both spark plugs and coil bolts. Clear any stored codes after the job and confirm a smooth idle and clean acceleration on a short test drive.

Quality matters here — OE‑equivalent coils from recognised brands tend to last longer and perform more consistently, especially in Aussie and Kiwi heat.

FAQs

How many ignition coils does a 2012 Subaru Forester have?
Both the 2.5i (FB25) and 2.5XT (EJ255) engines use four coil‑on‑plug ignition coils — one for each cylinder. There’s no separate central coil or long plug leads on this model year.

Do the coils need to be replaced as a set?
Not usually. It’s fine to replace only the faulty unit after proper diagnosis. On high‑kilometre cars, some owners choose to replace the coil boots or the full set proactively, but it isn’t mandatory if the others test fine.

Can driving with a failing coil damage other parts?
Yes. A persistent misfire can let unburnt fuel hit the catalytic converter, which may overheat and fail. If the Forester starts misfiring, minimise driving and sort it out promptly to protect the cat and the engine.