Parts for your 2004 Subaru Forester-Ignition coils

2004 Subaru Forester ignition coils — what they do and when to replace them

Ignition coils are absolutely used on the 2004 Subaru Forester. Technical references such as the Subaru Factory Service Manual for the SG-series (MY2004) and the Subaru genuine parts catalogue list the ignition coil as part of the standard ignition system. On naturally aspirated models (EJ251/EJ253), there’s a single four-tower coil pack with leads to each plug. On the turbocharged Forester XT (EJ255), it’s coil-on-plug with an individual coil at each cylinder. Either way, the Forester relies on coils to transform battery voltage into the high voltage needed to jump the spark plug gap and ignite the air–fuel mix.

For owners, the ignition coils are quiet achievers. When they’re healthy, the engine starts cleanly, idles smoothly, and pulls well through the revs. When they’re tired, you’ll likely cop misfires under load, rough idle, hard starts, higher fuel use, and a glowing check-engine light (often P030x codes). Because coils live in heat and vibration, ageing and internal insulation breakdown are normal over time.

There isn’t a fixed replacement interval on these cars, but a good rule is: inspect at major services and replace on condition. For NA models, the coil pack sits on the intake manifold, cracks, carbon tracking, swollen insulation, or corroded terminals are red flags. On XT models, the individual coils live under the intercooler—pulling the intercooler makes access easier. Look for brittle boots, oil intrusion from rocker cover leaks, or water damage.

Handy servicing tips for a 2004 Forester’s ignition coils:

• Pair new coils with the correct spark plugs (Subaru/NGK spec, proper heat range) and set the gap to spec.
• Use dielectric grease on boots and keep terminals clean and dry, replace tired leads on NA models.
• Check battery and charging voltage—low system voltage can mimic coil faults.
• If chasing a single-cylinder misfire on an XT, swap coils between cylinders to confirm the fault before buying parts.
• Avoid rock-bottom aftermarket coils, OE or reputable brands behave better with Subaru’s ignition dwell strategy.

When one coil fails on the NA coil-pack setup, it can affect its paired cylinder (waste-spark). On COP XT models, one dud coil will take out only that cylinder. Either way, keeping the coils, plugs, and leads/boots in good nick helps the Forester run sweet, use less fuel, and pass a WOF/reg with fewer dramas.

Does a 2004 Forester have one coil or four?

It depends on the engine. Naturally aspirated models use a single four-tower coil pack with plug leads. The turbocharged Forester XT uses coil-on-plug, so there’s one small coil on each spark plug under the intercooler.

How often should ignition coils be replaced?

There’s no set kilometre interval. Inspect them during major services and replace on condition. Many last well past 150,000 km, but heat, oil leaks, and age can shorten their life. If you’ve got recurring misfires, rough idle, or coil-related fault codes, test and replace as needed.

What symptoms point to a failing ignition coil?

Common signs include hard starting, rough idle, hesitation under load, poor fuel economy, and a check-engine light (often P0301–P0304). Visual cracks, carbon tracking, or oily, brittle boots are also giveaways. On XT models, a quick coil swap between cylinders is a handy diagnostic step.