Parts for your 2004 Subaru Impreza-Ignition coils

2004 Subaru Impreza ignition coils

Ignition coils are absolutely relevant and used on the 2004 Subaru Impreza. Technical sources including the Subaru Factory Service Manual for MY2004 (Engine Diagnostics), Subaru Technical Information System wiring diagrams, and OEM application catalogues from Subaru, NGK and Denso confirm two setups: non‑turbo EJ251/EJ253 models use a single dual‑secondary coil pack with plug leads (wasted‑spark), while WRX/STI models with EJ205/EJ207/EJ257 engines run individual coil‑on‑plug units. Either way, the car relies on ignition coils to light the fire every time.

The job of the ignition coil is to step the battery’s 12 volts up to the tens of thousands needed to jump the spark plug gap, right when the ECU commands it. On coil‑on‑plug WRX/STI cars, each cylinder gets its own coil for crisp timing and spark energy under boost. On non‑turbo models, the coil pack fires paired cylinders in a wasted‑spark arrangement that’s simple and reliable.

There’s no fixed replacement interval for coils, they’re serviced on condition. As part of routine servicing, it’s smart to scan for misfire codes, check for rough running, and visually inspect the coils or coil pack, plug leads (on non‑turbo), and plug tube areas for oil, corrosion or cracked insulation. Keeping battery voltage healthy and grounds clean reduces coil stress. When refitting, a dab of dielectric grease on boots helps future removal and keeps moisture at bay.

Common signs a 2004 Impreza needs coil attention include:

• Hard starting, rough idle, flat spots or poor fuel economy
• Check Engine Light with misfire or coil primary/secondary codes (e.g., P0301–P0304, P0351–P0354)
• Visible cracks, carbon tracking, swollen boots, or oil in plug wells

Replacement is straightforward with basic tools. Disconnect the battery, remove the engine cover if fitted, and work one cylinder at a time to avoid mixing connectors. For WRX/STI, torque the coil retainers to the factory spec and don’t yank on the wiring. For non‑turbo models, inspect or replace the plug leads with the coil pack, and consider fresh spark plugs while you’re there. Quality OEM‑equivalent coils are worth it, they last and behave. If one coil fails on a high‑kilometre turbo car, replacing just the culprit is fine, though many owners opt to do a pair or a full set to keep things tidy.

Popular questions

Does a 2004 Subaru Impreza have ignition coils?
Yes. Non‑turbo models use a single coil pack with leads, while WRX/STI models use individual coil‑on‑plug units. This layout is confirmed by the Subaru Factory Service Manual and OEM parts catalogues for MY2004.

How often should ignition coils be replaced?
There’s no set kilometre interval. Coils are replaced when fault symptoms or diagnostic codes appear. At each service, check for misfires, inspect the coils/pack and leads, and keep spark plugs up to date per the service schedule.

Is it OK to drive with a failing ignition coil?
It’s not recommended. Driving with a misfire can overheat and damage the catalytic converter and wash down cylinder walls. If it’s missing, keep trips short and get it sorted promptly.